Frequently Asked
Questions
on
Tropical
Cyclones
What is a tropical cyclone?
Why do 'tropical cyclones' winds rotate counter-clockwise (clockwise) in the Northern (Southern) Hemisphere?
What does "maximum sustained wind" mean ? How does it relate to gusts in tropical cyclones?
What is the energy potential of a tropical cyclone?
How are low pressure system classified in India? What are the differences between low, depression and cyclone?
Are all cyclonic storms equally dangerous?
What are the super cyclone, super-typhoon, a major hurricane and an intense hurricane?
Where do tropical cyclones form?
What is the size of a tropical cyclone over the north Indian Ocean ?
What is the structure of a Tropical Cyclone?
What is a "CDO"?
What is the "eye"? How is it formed and maintained? What is the "eyewall"? What are "spiral bands"?
How does the cyclone look like in a Radar ?
What is the wind structure in a cyclone?
How do the cyclones form and intensify?
What is the role of easterly wave on cyclogenesis in north Indian Ocean ?
Is there any extra-tropical cyclone?
What is the annual frequency of Cyclones over the Indian Seas? What is its intra-annual variation?
What are the average, most, and least tropical cyclones occurring in this basin?
How many severe tropical storms occur around the world and over north Indian Ocean every year?
How many cyclones cross different coastal states of India?
Which is the most intense tropical cyclone on record?
Which are the largest and smallest tropical cyclones on record?
Which tropical cyclone over north Indian Ocean have caused the most deaths and most damage?
Why there are fewer cyclones over the Arabian Sea as compared to the Bay of Bengal?
Why there are very few Tropical Cyclones during southwest monsoon season?
What is the life period of cyclones? Which tropical cyclone lasted the longest?
How are Tropical Cyclones monitored by IMD?
How is cyclone monitored by satellite technique ?
What is the utility of Radar in cyclone monitoring ?
What is the present network of Cyclone Detection Radars?
What are the basic differences between conventional analog type of Cyclone Detection Radar and the Doppler Weather Radar?
What are the causes of disaster during cyclone?
When does a coastal station start experiencing bad weather associated with a Cyclone?
What is the amount of rainfall expected during a cyclone? Which sector gets more rainfall? What is the impact of heavy rainfall ?
What are the largest rainfalls associated with tropical cyclones over north Indian Ocean?
What may be the wind speed in most severe storm?
What is the wind speed at the centre of a storm? What is weather there?
How is the damage that cyclones cause related with wind ?
Which sector of the cyclone experiences strongest winds?
What causes each cyclone to have a different maximum wind speed for a given minimum sea-level pressure?
Why do very severe cyclone or hurricane force winds start at 64 knots ?
What is a Storm Surge?
In which direction of a storm the surge will appear?
What is storm tide?
What is the interaction of astronomical tide with storm surge?
What are the disaster potential of Storm Surge?
What is the vulnerability our coastline from the point of view of storm surge potential?
Can we predict storm surge?
Which tropical cyclone has produced the highest storm surge?
What is the damage potential of a deep depression (28 – 33 knots) and what are the suggested actions?
What is the damage potential of a cyclonic storm (34-47 knots or 62 to 87 kmph) and what are the suggested actions?
What is the damage potential of a severe cyclonic storm 48-63 Knots (88-117 Kmph) and what are the suggested actions?
What is the damage potential of a very severe cyclonic storm (64-90 Knots or 118-167 Kmph) and what are the suggested actions?
What is the damage potential of a very severe cyclonic storm (91-119 Knots or 168-221 Kmph) and what are the suggested actions?
What is the damage potential of a super cyclonic storm 120 Knots (222 Kmph) & above? What are the suggested actions?
What is the normal movement of a Tropical Cyclone?
What are fast and slow moving cyclones?
How track prediction is done in IMD ?
What are the numerical weather prediction models used operationally for Tropical Cyclone track Prediction and storm surges in IMD?
What is our accuracy of landfall prediction?
How does IMD predict intensity of the cyclone ?
What is the role of upper tropospheric westerly trough ?
Why Tropical Cyclones weaken over land after landfall ?
Doesn't the friction over land kill tropical cyclones?
What are the abnormal characteristics associated with Tropical Cyclones?
What is the organizational set up in IMD for Cyclone forecasting and Warning?
What are the different bulletins issued by IMD in connection with the cyclone?
What is 4-stage warning system for Tropical Cyclones?
How frequently IMD issues these bulletins?
Is there any order in mentioning the disastrous weather in the bulletin?
What is port warning?
What are fishermen warning?
What is sea area bulletin?
What is coastal weather bulletin?
What is the meaning of widespread /fairly wide spread/scattered/isolated rainfall?
What do you mean by heavy rainfall, very heavy rainfall and extremely heavy rainfall ?
How does IMD mention state of sea in the bulletins?
What is meaning of the reference time mentioned in the bulletin ?
How are Cyclone Warnings disseminated ?
What are the bulletins available in the website? What is the website address ?
What is IVRS ? How does it work ?
What is Cyclone Warning Dissemination System (CWDS)?
Who are the recipients of Cyclone Warnings?
How a common man gets information about a cyclonic storm?
On the event of any doubt about approach of a cyclonic storm to whom a common man can approach to get authentic information (in absence of relevant AIR bulletins)?
How does IMD keep liaison with State officials?
What are the devastations which can not be protected by a common man and has to be mentally prepared to accept the loss?
How to understand that the cyclonic storm has weakened/moved away?
What are the pre-cyclone/during the cyclone/post cyclone responsibilities of a common man?
How IMD coordinates with National Disaster Management Division (NDM) of the Ministry of Home Affairs?
What is the role of IMD Tropical Cyclone management of north Indian Ocean Rim countries?
What are the bulletins issued by RSMC, New Delhi?
What is UTC? How do I tell at what time a satellite picture was taken?
What is relation between kmph and knots (or m/s) ?
Why are tropical cyclones named?
How can I nominate a new name for the list?
Can we tame a tropical Cyclone to reduce its damage potential?
What are the different methods tried to modified the cyclone?
What are the future plans of IMD to strengthen the Cyclone warning setup?
A tropical cyclone is a rotational low
pressure system in tropics when the central pressure falls by 5 to 6
hPa from the surrounding and maximum sustained wind speed reaches 34
knots (about 62 kmph). It is a vast violent whirl of 150 to 800 km,
spiraling around a centre and progressing along the surface of the
sea at a rate of 300 to 500 km a day.
The word cyclone has been derived from
Greek word ‘cyclos’ which means ‘coiling of a
snake’. The word cyclone was coined by Heary Piddington who
worked as a Rapporteur in Kolkata during British rule. The terms
"hurricane" and "typhoon" are region specific
names for a strong "tropical cyclone". Tropical cyclones
are called “Hurricanes” over the Atlantic Ocean and
“Typhoons” over the Pacific Ocean.
Why
do 'tropical cyclones' winds rotate counter-clockwise (clockwise) in
the Northern (Southern) Hemisphere?
As the earth's rotation
sets up an apparent force (called the Coriolis force) that pulls
the winds to the right in the Northern Hemisphere (and to the left
in the Southern Hemisphere). So, when a low pressure starts to form
over north of the equator, the surface winds will flow inward trying
to fill in the low and will be deflected to the right and a
counter-clockwise rotation will be initiated. The opposite (a
deflection to the left and a clockwise rotation) will occur south of
the equator.
This Coriolis force is too tiny to
effect rotation in, for example, water that is going down the drains
of sinks and toilets. The rotation in those will be determined by
the geometry of the container and the original motion of the water.
Thus, one can find both clockwise and counter-clockwise flowing drains no
matter what hemisphere you are located. If you don't believe this,
test it out for yourself.
What
does "maximum sustained wind" mean ? How does it relate to
gusts in tropical cyclones?
India Meteorological Department (IMD) uses a 3 minutes averaging for
the sustained wind. The maximum sustained wind mentioned in the bulletins used
by IMD is the highest 3 minutes surface wind occurring
within the circulation of the system. These surface winds
are observed (or, more often, estimated) at the standard meteorological height of
10 m (33 ft) in an unobstructed exposure (i.e., not blocked by
buildings or trees).
The
National Hurricane Centre uses a 1 minute
averaging time for reporting the sustained wind. Some countries also
use 10 minutes averaging time for this purpose. While one can utilize
a simple ratio to convert from peak 10 minute wind to peak 1 minute wind or
3 minute wind, such systematic differences to make interbasin comparison
of tropical cyclones around the world is problematic. However there
is no significant difference between the maximum sustained wind
reported in different basis with different averaging method.
What is
the energy potential of a tropical cyclone?
Tropical Cyclone can be compared to a
heat engine. The energy input is from warm water and humid air over
tropical oceans. Release of heat is through condensation of water
vapour to water droplets/rain. Only a small percentage (3%) of this
released energy is converted into Kinetic energy to maintain cyclone
circulation (windfield). A mature cyclone releases energy equivalent
to that of 100 hydrogen bombs.
How
are low pressure system classified in India? What are the differences
between low, depression and cyclone?
The low
pressure system over Indian region are classified based on the maximum
sustained winds speed associated with the system and the pressure
deficit/ number of closed isobars associated with the system.
The pressure criteria is used, when the system is over land and
wind criteria is used, when the system is over the sea. The system is
called as low if there is one closed isobar in the interval of 2 hPa.
It is called depression, if there are two closed isobars, a deep
depression, if there are three closed isobars and cyclonic storm if
there are four or more closed isobars. The detailed classification
based on wind criteria are given in the Table below. Considering
wind criteria, the system with wind speed of 17-27 knots is called as
depression and the low pressure system with maximum
sustained 3 minutes surface winds between
28-33 knots is called a deep depression. The system with maximum
sustained 3 minutes surface winds of
34 knots or more is called as cyclonic storm
|
System
|
Pressure
deficient
hPa
|
Associated
wind speed
Knots
(Kmph)
|
|
Low pressure area
|
1.0
|
<17(<32)
|
|
Depression
|
1.0- 3.0
|
17-27 (32–50)
|
|
Deep Depression
|
3.0 - 4.5
|
28-33 (51–59)
|
|
Cyclonic Storm
|
4.5- 8.5
|
34-47 (60-90)
|
|
Severe Cyclonic Storm (SCS)
|
8.5-15.5
|
48-63 (90-119)
|
|
Very Severe Cyclonic Storm
|
15.5-65.6
|
64-119 (119-220)
|
|
Super Cyclonic Storm
|
>65.6
|
>119(>220)
|
Are
all cyclonic storms equally dangerous?
No, all cyclonic storms are not
equally dangerous. More the pressure drop at the central region more
will be the severity of the storm. The cyclonic storms are generally
categorised according to the maximum wind associated with the storm.
If the maximum wind is between 34 - 47 knots (about 60-90 kmph) it is
called a Cyclonic storm. Severe Cyclonic storm will have maximum wind
speed between 48 - 63 knots (about 90-120 kmph). If the maximum
wind is 64-119 knots it will be called a very severe Cyclonic storm
and when the wind is 120 knots and above it will be called super
cyclonic storm. There
is very little association between intensity (either measured by
maximum sustained winds or by the lowest central pressure) and size
(measured by radius of gale force winds)
What
are the super cyclone, super-typhoon, a major hurricane and an
intense hurricane?
When
the
maximum
sustained 3 minutes surface winds are more than 119 knots, the low
pressure system is called as "Super Cyclone" over north Indian Ocean.
Similarly, “Super-typhoon"
is a term utilized by the U.S. Joint Typhoon Warning Centre for
typhoons that reach maximum
sustained 1 minute surface winds
of at least 130 knots (65 m/s). This is the equivalent of a strong
Saffir-Simpson
category 4 or category 5 hurricane
in the Atlantic basin or a category
5 severe
tropical cyclone in the Australian basin.
Where
do tropical cyclones form?
The
tropical cyclones form over ocean basins in lower latitudes of all
oceans except south Atlantic and southeast Pacific. The tropical
cyclones develop over the warm water of the Bay of Bengal and the
Arabian Sea. The favourable ocean basins for development of cyclonic
storms are shown in the figure below.
TC
breeding grounds are located over certain ocean basins. Arrows
indicate average trajectories over different basins
What
is the size of a tropical cyclone over the north Indian Ocean
The
size of a tropical cyclone over Indian seas varies from 50-100 km
radius to 2000 km with an average of 300 –600 km.
What
is the structure of a tropical cyclone?
A
fully developed tropical cyclone has a central cloud free region of
calm winds, known as the “eye”
of the cyclone with diameter varying from 10 to 50 km. Surrounding
the eye is the “wall
cloud region”
characterised by very strong winds and torrential rains, which has the
width of about 10 to 150 km. The winds over this region rotate around
the centre and resemble the “coils of a snake”. Wind
speed fall off gradually away from this core region, which terminate
over areas of weaker winds with overcast skies and occasional squall
.There may be one or more spiral branch in a cyclone where higher
rainfall occurs. The vertical extent of the cyclone is about 15 km.
The INSAT imagery of Orissa Super cyclone on 29th
October, 1999 is shown in the figure below.
What
is a "CDO"?
"CDO"
is an acronym that stands for "central
dense overcast".
This is the cirrus cloud shield that results from the thunderstorms
in the eyewall of a tropical cyclone and its rainbands. Before the
tropical cyclone reaches very severe cyclonic storm (64 knots,),
typically the CDO is uniformly showing the cold cloud tops of the
cirrus with no eye apparent. Once the storm reaches the hurricane
strength threshold, usually an eye can be seen in either the infrared
or visible channels of the satellites. Tropical cyclones that have
nearly circular CDO's are indicative of favourable, low vertical
shear environments.
What
is the "eye"? How is it formed and maintained? What is the
"eyewall"? What are "spiral bands"?
The
"eye"
is a roughly circular area of comparatively light winds and fair
weather found at the centre of a severe tropical cyclone. Although
the winds are calm at the axis of rotation, strong winds may extend
well into the eye. There is little or no precipitation and sometimes
blue sky or stars can be seen. The eye is the region of lowest
surface pressure and warmest temperatures aloft - the eye temperature
may be 10°C warmer or more at an altitude of 12 km than the
surrounding environment, but only 0-2°C warmer at the surface in
the tropical cyclone. Eyes range in size from 8 km to over 200 km
across, but most are approximately 30-60 km in diameter.
The
eye is surrounded by the "eyewall",
the roughly circular ring of deep convection, which is the area of
highest surface winds in the tropical cyclone. The eye is composed of
air that is slowly sinking and the eyewall has a net upward flow as a
result of many moderate - occasionally strong - updrafts and
downdrafts. The eye's warm temperatures are due to compressional
warming of the subsiding air. Most soundings taken within the eye
show a low-level layer, which is relatively moist, with an inversion
above - suggesting that the sinking in the eye typically does not
reach the ocean surface, but instead only gets to around 1-3 km of
the surface.
The exact mechanism by which the eye
forms remains somewhat controversial. One idea suggests that the eye
forms as a result of the downward directed pressure gradient
associated with the weakening and radial spreading of the tangential
wind field with height (Smith, 1980). Another hypothesis suggests
that the eye is formed when latent heat release in the eyewall
occurs, forcing subsidence in the storm's centre (Shapiro and
Willoughby, 1982). It is possible that these hypotheses are not
inconsistent with one another. In either case, as the air subsides,
it is compressed and warms relative to air at the same level outside
the eye and thereby becomes locally buoyant. This upward buoyancy
approximately balances the downward directed pressure gradient so
that the actual subsidence is produced by a small residual force.
Another
feature of tropical cyclones that probably plays a role in forming
and maintaining the eye is the eyewall convection. Convection in
tropical cyclones is organized into long, narrow rainbands which are
oriented in the same direction as the horizontal wind. Because these
bands seem to spiral into the centre of a tropical cyclone, they are
called "spiral
bands".
Along these bands, low-level convergence is a maximum, and therefore,
upper-level divergence is most pronounced above. A direct circulation
develops in which warm, moist air converges at the surface, ascends
through these bands, diverges aloft, and descends on both sides of
the bands. Subsidence is distributed over a wide area on the outside
of the rainband but is concentrated in the small inside area. As the
air subsides, adiabatic warming takes place, and the air dries.
Because subsidence is concentrated on the inside of the band, the
adiabatic warming is stronger inward from the band causing a sharp
contrast in pressure falls across the band since warm air is lighter
than cold air. Because of the pressure falls on the inside, the
tangential winds around the tropical cyclone increase due to
increased pressure gradient. Eventually, the band moves toward the
centre and encircles it and the eye and eyewall form.
Thus, the cloud-free eye may be due to
a combination of dynamically forced centrifuging of mass out of the
eye into the eyewall and to a forced descent caused by the moist
convection of the eyewall. This topic is certainly one that can use
more research to ascertain which mechanism is primary.
Some
of the most intense tropical cyclones exhibit concentric eyewalls,
two or more eyewall structures centreed at the circulation centre of
the storm. Just as the inner eyewall forms, convection surrounding
the eyewall can become organized into distinct rings. Eventually, the
inner eye begins to feel the effects of the subsidence resulting from
the outer eyewall, and the inner eyewall weakens, to be replaced by
the outer eyewall. The pressure rises due to the destruction of the
inner eyewall are usually more rapid than the pressure falls due to
the intensification of the outer eyewall, and the cyclone itself
weakens for a short period of time.
How
does the cyclone look like in a Radar ?
According
to Radar imagery, a matured cyclone consists of eye, eye wall, spiral
bands, pre-cyclone squall lines and streamers as shown in the above
figure.
What is the wind structure
in a cyclone?
The
ideal wind and cloud distribution in a cyclone is shown in the
following figure.
The
band of maximum winds may vary between 10 and 150 Km. In this belt,
speed decreases rapidly towards the eye of the cyclone. But it
decreases slowly and in an irregular fashion outward from the eye
wall.
How
do the cyclones form and intensify?
In the tropics, weak
pressure waves move from east to west. These are called easterly waves. Under
favourable situation, a low pressure area forms over the area of an easterly trough.
This gives rise to low level convergence. If the sea is warm (sea surface
temperature > =
26.50 C) and there is sufficient upper
level divergence i.e air is blown off at higher levels from the area of low
pressure, the pressure gradually falls. Low level convergence coupled with upper
level divergence gives rise to vertical motion taking moist air upwards. These
moistures condense at higher levels (middle troposphere) and give out latent
heat of condensation. Due to release of heat of condensation the area warms up
resulting into further fall in pressure. This process continues and a low
pressure
system
gradually intensifies into a cyclonic storm.
Hence,
for tropical cyclogenesis, there are several favourable environmental conditions
that must be in place. They are:-
-
Warm
ocean waters (of at least 26.5°C) throughout a sufficient depth (unknown how
deep, but at least on the order of 50 m). Warm waters are necessary to fuel
the heat engine of the tropical cyclone.
-
An
atmosphere which cools fast enough with height such that it is potentially
unstable to moist convection. It is the thunderstorm activity which allows the
heat stored in the ocean waters to be liberated for the tropical cyclone
development.
-
Relatively moist layers near the mid-troposphere (5 km).
Dry mid levels are not conducive for allowing the continuing development of
widespread thunderstorm activity.
-
A
minimum distance of at least 500 km from the equator. For tropical
cyclogenesis to occur, there is a requirement for non-negligible amounts of
the Coriolis Force (attributed to earth’s rotation) to provide the near
gradient wind balance to occur. Without the Coriolis Force, the low pressure
of the disturbance cannot be maintained. This is the reason why the narrow
corridor of width of about 300 km on either side of the equator is free from
cyclones. Because of this there is no inter-hemispheric migration of tropical
cyclones across the equator.
-
A
pre-existing near-surface disturbance with sufficient vorticity (rotation) and
convergence. Tropical cyclones cannot be generated spontaneously. To develop,
they require a weakly organized system with sizable spin and low level inflow.
-
Low
values (less than about 10 m/s or 20 kts) of vertical wind shear between the
lower (1.5 km) and the upper troposphere (12 km). Vertical wind shear is the
magnitude of wind change with height. Large values of vertical wind shear
disrupt the incipient tropical cyclone and can prevent genesis, or, if a
tropical cyclone has already formed, large vertical shear can weaken or
destroy the tropical cyclone by interfering with the organization of deep
convection around the cyclone centre.
The
above conditions are necessary, but not sufficient as many disturbances that
appear to have favourable conditions do not develop. However, these criteria fit
well over the north Indian Ocean
What is
the role of easterly waves on cyclogenesis in north Indian Ocean
?
It has been recognized since at least the 1930s that lower
tropospheric westward traveling disturbances often serve as the "seedling"
circulations for a large proportion of tropical cyclones. These disturbances are
known as easterly
waves. The waves move generally toward
the west in the lower tropospheric trade wind flow. They are first seen usually
in October to April. The waves have a period of about 3 or 4 days and a
wavelength of 2000 to 2500 km. One should keep in mind that the "waves" can be
more correctly thought of as the convectively active troughs along an extended
wave train. Though, these waves are generated frequently, but it appears that
the number that is formed has no relationship to how much
tropical cyclone activity there is over the north Indian Ocean each year. It is
currently completely unknown, how, easterly waves change from year to year in
both intensity and location and how these might relate to the activity
?
Is there
any extra-tropical cyclone?
Extra-tropical cyclones are low pressure systems with
associated cold fronts, warm fronts, and occluded fronts. The
extra-tropical cyclone is a
storm system that primarily gets its energy from the horizontal temperature
contrasts that exist in the atmosphere. Extra-tropical cyclones are low pressure
systems with associated cold fronts, warm fronts, and occluded fronts.
Tropical
cyclones, in contrast, typically have
little to no temperature differences across the storm at the surface and their
winds are derived from the release of energy due to cloud/rain formation from
the warm moist air of the tropics. Structurally, tropical cyclones have their
strongest winds near the earth's surface, while extra-tropical cyclones have
their strongest winds near the tropopause - about 12 km up. These differences
are due to the tropical cyclone being "warm-core" in the troposphere (below the
tropopause) and the extra-tropical cyclone being "warm-core" in the stratosphere
(above the tropopause) and "cold-core" in the troposphere. "Warm-core" refers to
being relatively warmer than the environment at any level.
Often,
a tropical cyclone will transform into an extra-tropical cyclone as it recurves
poleward and to the east. Occasionally, an extra-tropical cyclone will lose its
frontal features, develop convection near the centre of the storm and transform
into a full-fledged tropical cyclone. Such a process is most common in the north
Atlantic and northwest Pacific basins. The transformation of tropical cyclone
into an extra-tropical cyclone (and vice versa) is currently one of the most
challenging forecast problems.
What is the annual frequency of Cyclones over the Indian
Seas? What is its intra-annual variation?
The
average annual frequency of tropical cyclones in the north Indian Ocean (Bay of
Bengal and Arabian Sea) is about 5 (about 5-6 % of the Global annual average)
and about 80 cyclones form around the globe in a year. The frequency is more in
the Bay of Bengal than in the Arabian Sea, the ratio being 4:1. The monthly
frequency of tropical cyclones in the north Indian Ocean display a bi-modal
characteristic with a primary peak in November and secondary peak in May. The
months of May-June and October-November are known to produce cyclones of severe
intensity. Tropical cyclones developing during the monsoon months (July to
September) are generally not so intense.
The frequencies of Cyclonic
systems over north Indian Ocean during 1891-2006 are given in the figure
below.
What are the average, most, and
least tropical cyclones occurring in this basin?
The most, least and average numbers
of cyclonic storms and severe cyclonic storms over the north Indian ocean is
given in the Table below:
-
Minimum No. of cyclones in a year - One (1949)
-
Maximum No. of cyclones in a year – Ten
(1893,1926,1930,1976)
-
Out of total disturbances - 35%
intensify to Cyclones
16 % intensify to severe
cyclones
07% intensify to very severe
cyclones
|
Basin
|
Cyclonic
storm
|
Severe cyclonic
storm
|
|
Most
|
Least
|
Average
|
Most
|
Least
|
Average
|
|
N Indian Ocean
|
10
|
1
|
5.4
|
6
|
0
|
2.5
|
How many severe tropical storms occur around the world and
over north Indian Ocean every year?
About
20-30 severe tropical storms occur around the world every year. Over the north
Indian Ocean, 2-3 severe cyclonic storms form out of total 5-6 cyclonic
storms
How many
cyclones cross different coastal states of India?
The frequencies of
cyclonic storms crossing different coastal states of India during 1891-2006 are
shown in the figure below. The frequency of severe cyclonic storms is maximum
for Andhra Pradesh while that of cyclone is maximum for Orissa. Considering west
coast only, Gujarat is most vulnerable.
Which is
the most intense tropical cyclone on record?
Typhoon
Tip in the Northwest Pacific Ocean on 12 October, 1979 was measured to have a
central pressure of 870 hPa and estimated surface sustained winds of 165 knots
(85 m/s). Typhoon Nancy on 12 September, 1961 is listed in the best track data
for the Northwest Pacific region as having an estimated maximum sustained
winds of 185 knots (95 m/s) with a
central pressure of 888 hPa. However, it is now recognized that the
maximum sustained
winds estimated for typhoons during the
1940s to 1960s were too strong and that the 95 m/s (and numerous 83 to 93 m/s
reports) is somewhat too high.
Note that
Hurricane Gilbert's 888 hPa lowest pressure (estimated from flight level data)
in mid September, 1988 is the most intense [as measured by lowest sea level
pressure] for the Atlantic basin, it is almost 20 hPa weaker (higher) than the
above Typhoon Tip of the Northwest Pacific Ocean.
While the
central pressures for the Northwest Pacific typhoons are the lowest globally,
the North Atlantic hurricanes have provided sustained wind speeds possibly
comparable to the Northwest Pacific. From the best track database, both
Hurricane Camille (1969) and Hurricane Allen (1980) have winds that are
estimated to be 165 knots (85 m/s). Measurements of such winds are inherently
going to be suspect as instruments often are completely destroyed or damaged at
these speeds.
Orissa
super cyclone, 1999 which crossed Orissa coast near Paradip on
29th October,
1999 was the most intense cyclonic storm over north Indian Ocean in the recorded
history of the region. The estimated sustained maximum surface wind speed was
about 140 knots at the time of landfall and lowest estimated central pressure
was 912 hPa.
A few cyclones that have originated over the Bay of Bengal
have reached the intensity of Super Cyclones and have caused great devastations
to life and property. The estimates of maximum sustained winds of these systems
are estimated from satellite imageries. The list of very intense Cyclones in the
Bay of Bengal since 1990 is given below.
|
.Place of
landfall
|
Date
of landfall
|
Maximum sustained winds (kmph) - estimated on the
basis of satellite imageries
|
|
Chittagong
|
13 November,
1970
|
224
|
|
Chirala, Andhra
Pradesh
|
19 November,
1977
|
260
|
|
Rameshwaram
|
24 November
1978
|
204
|
|
Sriharikota
|
14 November,
1984
|
213
|
|
Bangla Desh
|
30 November,
1988
|
213
|
|
Kavali, Andhra
Pradesh
|
9 November,
1989
|
235
|
|
Machlipatnam,
AP
|
9 May ,1990
|
235
|
|
Chittagong
|
29 April, 1991
|
235
|
|
Teknaf
(Myanmar)
|
2 May, 1994
|
204
|
|
Teknaf
|
19 May, 1997
|
235
|
|
Paradip, Orissa
|
29 October,
1999
|
260
|
|
89.80E, Bangladesh
|
15 November,
2007
|
220
|
|
16.00N, Myanmar
|
02 May, 2008
|
200
|
Which are
the largest and smallest tropical cyclones on record?
Typhoon
Tip had gale force winds 34 knots (17 m/s), which extended out for 1100 km in
radius in the Northwest Pacific on 12 October, 1979. Tropical Cyclone Tracy had
gale force winds that only extended 50 km radius when it struck Darwin,
Australia, on 24 December,1974.
Considering north Indian Ocean,
Orissa super cyclone of October, 1999 and the cyclone, ‘Ogni’ were the largest
and smallest cyclones during 1891-2007.
Which
tropical cyclone over north Indian Ocean have caused the most deaths and most
damage?
The death toll in the
infamous Bangladesh Cyclone of 1970 has had several estimates, some wildly
speculative, but it seems certain that at least 300,000 people died from the
associated storm tide [surge] in the low-lying deltas.
Why there are fewer cyclones over the Arabian Sea as
compared to the Bay of Bengal?
Cyclones
that form over the Bay of Bengal are either those develop insitu over southeast
Bay of Bengal and adjoining Andaman Sea or remnants of typhoons over Northwest
Pacific and move across south China sea to Indian Seas. As the frequency of
typhoons over Northwest Pacific is quite high (about 35 % of the global annual
average), the Bay of Bengal also gets its increased quota.
The
cyclones over the Arabian Sea either originate insitu over southeast Arabian Sea
(which includes Lakshadweep area also) or remnants of cyclones from the Bay of
Bengal that move across south peninsula. As the majority of Cyclones over the
Bay of Bengal weaken over land after landfall, the frequency of migration into
Arabian Sea is low.
In
addition to all the above the Arabian Sea is relatively colder than Bay of
Bengal and hence inhibits the formation and intensification of the
system.
Why there are very few Tropical Cyclones during southwest
monsoon season?
The
southwest monsoon is characterized by the presence of strong westerly winds in
the lower troposphere (below 5 km) and very strong easterly winds in the upper
troposphere (above 9 km) .This results in large vertical wind shear. Strong
vertical wind shear inhibits cyclone development.
Also the
potential zone for the development of cyclones shifts to North Bay of Bengal
during southwest monsoon season. During this season, the low pressure system
upto the intensity of depressions form along the monsoon trough, which extends
from northwest India to the north Bay of Bengal. The Depression forming over
this area crosses Orissa – West Bengal coast in a day or two. These systems have
shorter oceanic stay which is also one of the reasons for their
non-intensification into intense cyclones.
What is the
life period of cyclones? Which tropical cyclone lasted the
longest?
Life
period of a Tropical Cyclone over the north Indian Ocean is 5-6 days. It will
have hurricane intensity for 2-4 days as against 6 days of global average. Life
period of the longest lived Tropical cyclone in Indian seas is 14 days
(2nd -15th Nov, 1886 & 16th - 29th Nov, 1964). Hurricane/Typhoon John lasted 31
days as it traveled both the Northeast and Northwest Pacific basins during
August and September, 1994. (It formed in the Northeast Pacific, reached
hurricane force there, moved across the dateline and was renamed Typhoon John,
and then finally recurved back across the dateline and renamed Hurricane John
again.) Hurricane Ginger was a tropical cyclone for 28 days in the North
Atlantic Ocean back in 1971. It should be noted that prior to the weather
satellite era (1961) many tropical cyclones' life cycles could be underestimated.
How are Tropical Cyclones monitored by IMD?
IMD has a
well-established and time-tested organization for monitoring and forecasting
tropical cyclones. A good network of meteorological observatories (both surface
and upper air) is operated by IMD, covering the entire coastline and islands.
The conventional observations are supplemented by observational data from
automatic weather stations (AWS), radar and satellite systems. INSAT imagery
obtained at hourly intervals during cyclone situations has proved to be
immensely useful in monitoring the development and movement of cyclones.
How is
cyclone monitored by satellite technique ?
The
satellite technique can be used to find out the centre and intensity of the
system. It can also be used to find out various derived parameters which are
useful for monitoring and prediction of the cyclones and associated disastrous
weather.
Dvorak’s
technique based on pattern recognition in the cloud imagery based on satellite
observation is used to determine the intensity of cyclonic storm. For this
purpose a T. No. where T stands for tropical cyclone is assigned to the system.
This scale of T Nos. varies from T 1.0 to T 8.0 at the interval of 0.5. The T
2.5 corresponds to the intensity of a cyclonic storm. The detailed
classification of cyclonic disturbances based on above technique is given
below:
“T” CLASSIFICATION OF CYCLONIC STORM
AND
CORRESPONDING WIND SPEED AND PRESSURE DEFECT
(?P)
|
T. Number/
C.I.
Number
|
Classification of Cyclonic
Disturbance
|
Wind
speed in Knots
|
Wind
speed In Kmph
|
? P
|
Wind
criteria in Knots
|
Wind
criteria in Kmph
|
|
T1.0
|
L
|
|
|
|
?17
|
?31
|
|
T1.5
|
D
|
25
|
46.3
|
|
17-27
|
31-49
|
|
T2.0
|
DD
|
30
|
55.6
|
4.5
|
28-33
|
50-61
|
|
T2.5
|
CS
|
35
|
64.9
|
6.1
|
34-47
|
62-88
|
|
T3.0
|
|
45
|
83.4
|
10.0
|
|
|
|
T3.5
|
SCS
|
55
|
101.9
|
15.0
|
48-63
|
89-117
|
|
T4.0
|
VSCS
|
65
|
120.5
|
20.9
|
64-119
|
119-221
|
|
T4.5
|
|
77
|
142.7
|
29.4
|
|
|
|
T5.0
|
|
90
|
166.8
|
40.2
|
|
|
|
T5.5
|
|
102
|
189.0
|
51.6
|
|
|
|
T6.0
|
|
115
|
213.1
|
65.6
|
|
|
|
T6.5
|
SuCS
|
127
|
235.4
|
80.0
|
120 AND ABOVE
|
222 AND
ABOVE
|
|
T7.0
|
|
140
|
259.5
|
97.2
|
|
|
|
T7.5
|
|
155
|
287.3
|
119.1
|
|
|
|
T8.0
|
|
170
|
315.1
|
143.3
|
|
|
What is the utility of Radar in cyclone monitoring
?
The radar
can be utilized to find out the location of the cyclonic storm more accurately
when the system comes within radar range. In addition it can find out convective
cloud cluster, wind distribution, rainfall rate etc.
What is the present network of Cyclone Detection
Radars?
A network
of conventional Cyclone Detection Radars (CDRs) has been established at Kolkata,
Paradip, Visakhapatnam, Machilipatnam, Chennai and Karaikal along the east coast
and Goa, Cochin, Mumbai and Bhuj along the west coast. These conventional radars
are being phased out and replaced by Doppler Weather Radars (DWRs). DWR have
already been installed and made operational at Chennai, Kolkata, Visakhapatnam
and Machlipatnam. An indigenously developed DWR Radar by Indian Space Research
Organisation (ISRO) has been installed at Sriharikota.
It is
proposed to replace all the conventional radars by DWRs during the next 3-4
years.
What are the basic differences between conventional analog
type of Cyclone Detection Radar and the Doppler Weather Radar?
While
conventional weather radar can look deeper into a weather system to provide
information on intensity rain-rate, vertical extent, the capability to probe
internal motion of the hydrometers and hence to derive information on velocity
and turbulence structure has become available only with the advent of Doppler
Weather Radar (DWRs) which provide vital information on radial velocity from
which wind field of a tropical disturbance in the reconnaissance area of DWR can
be derived. In addition to above, a number of derived parameters useful for
cyclone monitoring and prediction are also available from DWR.
What are the causes of disaster during
cyclone?
The
dangers associated with cyclonic storms are generally three fold.
-
Very
heavy rains causing floods.
-
Strong
wind.
-
Storm
surge.
Let us
discuss each separately:
(i) The
rainfall associated with a storm vary from storm to storm even with the same
intensity. Record rainfall in a cyclonic storm has been as low as trace to as
high as 250 cms. It has been found that the intensity of rainfall is about 85
cms/day within a radius of 50 kms and about 35 cms/day between 50 to 100 kms
from the centre of the storm. Precipitation of about 50 cm/day is quite common
with a C.S. This phenomenal rain can cause flash flood.
(ii) The
strong wind speed associated with a cyclonic storm. (60-90 kmph) can result into
some damage to kutcha houses and tree branches likely to break off. Winds of a
severe Cyclonic storm (90-120 kmph) can cause uprooting of trees, damage to
pucca houses and disruption of communications. The wind associated with a very
severe Cyclonic storm and super cyclonic storm can uproot big trees, cause wide
spread damages to houses and installations and total disruption of
communications. The maximum wind speed associated with a very severe Cyclonic
storm that hit Indian coast in the past 100 years was 260 kmph in Oct., 1999
(Paradeep Super cyclone).
(iii) The
severest destructive feature of a tropical storm is the storm surge popularly
called tidal waves. The costal areas are subjected to storm surge and is
accentuated if the landfall time coincides with that of high tides. This is
again more if the sea bed is shallow. Storm surge as high as 15 to 20 ft. may
occur when all the factors contributing to storm surge are maximum. This storm
tide inundates low lying coastal areas which has far reaching consequences apart
from flooding. The fertility of land is lost due to inundation by saline water
for a few years to come.
When does a
coastal station start experiencing bad weather associated with a
Cyclone?
Coasts
come under the influence of bad weather in the form of heavy rain, gale winds
(exceeding 65 kmph) when the cyclone moves closer to the coast within 200km.
Heavy rainfall generally commences about 9-12 hours before cyclone landfall.
Gale force winds commence about 6-9 hours in advance of cyclone landfall.
Maximum storm surge may appear at or near the landfall time.
What is the
amount of rainfall expected during a cyclone? Which sector gets more rainfall?
What is the impact of heavy rainfall ?
Intensive
Rainfall occurs to the left of the Cyclone. Maximum rainfall occurs close to the
centre of the storm. Secondary maximum of rainfall occurs 2º away from Primary
maximum to the right of the storm centre. Slow moving/big size cyclones give
more rainfall, whereas, fast moving/small size ones give less rainfall. More
than 90% of rainfall is limited within 200 Km radius of the storm. Extensive
rainfall occurs in the left forward sector for westward moving system and
forward sector for northward moving system and right forward sector for those
re-curving to east and northeast.
The
governing factors for rainfall distribution and intensity are intensity, speed
and size of the storm and local effects such as topography and orientation
of the coast.
What are the
largest rainfalls associated with tropical cyclones over north Indian
Ocean?
The
rainfall can vary from trace/ nil rainfall when the system moves skirting the
coast to maximum rainfall upto 50-60 cm per day. In the recent super cyclone
which crossed Orissa coast near Paradip on 29th October 1999, Paradip recorded 24 hr cumulative rainfall of
about 52 cm at 0830 IST of 30th October 1999.
What may be the wind speed in most severe
storm?
The wind
speed may be as high as 300 kmph.
What is the wind speed at the centre of a storm? What is
weather there?
Nearly
calm wind with fair weather prevails at the centre of the storm.
How is the
damage that cyclones cause related with wind ?
The
amount of damage does not increase linearly with the wind speed. Instead, the
damage produced increases exponentially with the winds.
Which sector
of the cyclone experiences strongest winds?
In
general, the strongest winds in a cyclone are found on the right side of the
storm. The "right side of the storm" is defined with respect to the storm's
motion: if the cyclone is moving to the west, the right side would be to the
north of the storm; if the cyclone is moving to the north, the right side would
be to the east of the storm, etc. The strongest wind on the right side of the
storm is mainly due to the fact that the motion of the cyclone also contributes
to its swirling winds. A cyclone with a 145 kmph winds while stationary
would have winds up to 160 kmph on the right side and only 130 kmph on the
left side if it began moving (any direction) at 16 kmph. While writing the
cyclone warning bulletins, this asymmetry is taken into
consideration.
What causes
each cyclone to have a different maximum wind speed for a given minimum
sea-level pressure?
The basic
horizontal balance in a tropical cyclone above the boundary layer is between the
sum of the Coriolis 'acceleration' and the centripetal 'acceleration', balanced
by the horizontal pressure gradient force. This balance is referred to as
gradient
balance, where the Coriolis 'acceleration'
is defined as the horizontal velocity of an air parcel, v, times the Coriolis parameter, f. Centripetal 'force' is defined as the acceleration on a
parcel of air moving in a curved path, directed toward the centre of curvature
of the path, with magnitude v2/r, where v is the
horizontal velocity of the parcel and r the
radius of curvature of the path. The centripetal force alters the original
two-force geostrophic balance and creates a non-geostrophic gradient wind. The
reason that different peak winds can result in different central pressures is
caused by the fact that the radius, r, of the
peak wind varies. A storm with 40 m/s peak winds with a 100 km RMW will have a
much lower pressure drop than one with a 25 km RMW.
Why do very
severe cyclone or hurricane force winds start at 64 knots ?
In
1805-06, Commander Francis Beaufort RN (later Admiral Sir Francis Beaufort)
devised a descriptive wind scale in an effort to standardize wind reports in
ship's logs. His scale divided wind speeds into 14 Forces (soon after pared down
to thirteen) with each Force assigned a number, a common name, and a description
of the effects such a wind would have on a sailing ship. And since the worst
storm an Atlantic sailor was likely to run into was a hurricane that name was
applied to the top Force on the scale.
During the 19th Century,
with the manufacture of accurate anemometers, actual numerical values were
assigned to each Force level, but it wasn't until 1926 (with revisions in 1939
and 1946) that the International Meteorological Committee (predecessor of the
WMO) adopted a universal scale of wind speed values. It was a progressive scale
with the range of speed for Forces increasing as you go higher. Thus Force 1 is
only 3 knots in range, while the Force 11 is eight knots in range. So Force 12
starts out at 64 knots (74 mph, 33 m/s).
There is
nothing magical in this number, and since hurricane force winds are a rare
experience chances are the committee which decided on this number didn't do so
because of any real observations during a hurricane. Indeed the Smeaton-Rouse
wind scale in 1759 pegged hurricane force at 70 knots (80 mph, 36 m/s). Just the
same, when a tropical cyclone has maximum winds of approximately these speeds we
do see the mature structure (eye, eyewall, spiral rainbands) begin to form, so
there is some utility with setting hurricane force in this neighborhood.
What is a Storm Surge?
Storm
Surge is an abnormal rise of sea level as the cyclone crosses the coast. Sea
water inundates the coastal strip causing loss of life, large scale destruction
to property & crop. Increased salinity in the soil over affected area makes
the land unfit for agricultural use for two or three seasons.
Storm
surge depends on intensity of the cyclone (Maximum winds and lowest pressure
associated with it and Coastal bathymetry (shallower coastline generates surges
of greater heights).
In which direction of a storm the surge will
appear?
The on
shore wind gives rise to storm surge. Thus the forward right sector of a storm
gives rise to storm surge.
What is storm tide?
The storm
tide is the combination of storm surge and the astronomical tide
What is the interaction of astronomical tide with storm
surge?
In
general one may expect that if there is a storm surge of x metres and tidal wave
of y metres then during high tide total surges would be x+y and during low tide
x-y. But, it is found that there is an interaction of storm surge with
astronomical tide, and during high tide time the total surge is little less than
x+y and during low tide time it is little more than x-y.
What are the disaster potential of Storm
Surge?
Disaster
potential due to cyclones is due to high storm surges occurring at the time of
landfall. The storm surges are by far the greatest killers in a cyclone. as sea
water inundates low lying areas of the coastal regions causing heavy floods,
erosion of beaches and embankments, damage to vegetation and reducing soil
fertility. Flooding due to storm surges pollute drinking water sources resulting
in shortage of drinking water and causing out-break of epidemics, mostly water
borne diseases Very strong winds (Gales) may cause uprooting of trees, damage to
dwellings, overhead installations, communication lines etc., resulting in loss
of life and property. Past records show that very heavy loss of life due to
tropical cyclones have occurred in the coastal areas surrounding the Bay of
Bengal. Cyclones are also often accompanied by very intense & heavy
precipitation (exceeding 40-50 cm in a day or about 10cm or more per hour in
some places)
What is the vulnerability our coastline from the point of
view of storm surge potential?
Entire
Indian coast can be categorized into 4 zones
-
Very
high risk zones (Surge height > 5m)
-
High
risk Zone (Surge height between 3-5m)
-
Moderate risk zone (Surge height between 1.5 to
3m)
-
Minimal
risk zone ( Surge height < 1.5m)
Accordingly
-
The
coastal areas and off-shore islands of Bengal and adjoining Bangladesh are the
most storm-surge prone (~ 10-13m) – VHRZ
-
East
coast of India between Paradip and Balasore in Orissa (~ 5-7m) –
VHRZ
-
Andhra
coast between Bapatla and Kakinada holding estuaries of two major rivers
Krishna and Godavari (~ 5-7m) – VHRZ
-
Tamilnadu coast between Pamban and Nagapattinam (~ 3-5m) –
HRZ
-
Gujarat
along the west coast of India (~ 2-3m) -MRZ
Can we predict storm surge?
The storm
surge is predicted by IMD using nomograms and dynemic model developed by IIT,
Delhi. Both these models taken into consideration different characteristics, the
cyclones and the coastal bathymetry to predict the storm surge.
Which
tropical cyclone has produced the highest storm surge?
The
Bathurst Bay Hurricane, also known as Tropical Cyclone Mahina, struck Bathurst
Bay, Australia in 1899. It produced a 13 m (about 42 ft) surge, but other
contemporary accounts place the surge at 14.6 m (almost 48 ft). Considering
cyclones over north Indian Ocean, cyclone of 1970 has produced maximum storm
surge of 13 metres in recent years. Some of the significant storm surges
(metres) over the region are mentioned below.
Hooghly
river (WB), October, 1737 : 13
Contai
(WB), October, 1864 : 10-13
Bangladesh cyclone, November, 1970 : 13
Paradip,
Orissa,October, 1971 : 4-5
Balasore
Orissa, May, 1989 : 3-6
Orissa
Super Cyclone, October, 1999 : 5-6
What is the
damage potential of a deep depression (28 – 33 knots) and what are the suggested
actions?
Structures: Minor damage to loose/ unsecured structures Communication & power:
Road/Rail: Some breaches in Kutcha road due to flooding
Agriculture: Minor damage to Banana trees and near coastal agriculture
due to salt spray. Damage to ripe paddy crops
Marine
Interests: Very
rough seas. Sea waves about 4-6 m high.
Coastal
Zone: Minor damage
to Kutcha embankments
Overall
Damage Category:
Minor
Suggested
Actions: Fishermen
advised not to venture into sea
What is the
damage potential of a cyclonic storm (34-47 knots or 62 to 87 kmph) and what are
the suggested actions?
Structures: Damage to thatched huts
Communication and power: Minor damage to power and
communication lines
due to breaking of tree
branches.
Road/Rail: Major damage to Kutcha and minor damage to Pucca roads.
Agriculture: Some damage to paddy crops, Banana, Papaya trees and
orchards.
Marine
Interests: High to
very high sea waves about 6-9 m high.
Coastal
Zone: Sea water
inundation in low lying areas after erosion of Kutcha embankments
Overall
Damage Category:
Minor to Moderate
Suggested
Actions: Fishermen
advised not to venture into sea
What is the
damage potential of a severe cyclonic storm 48-63 Knots
(88-117 Kmph) and what are the suggested actions?
Structures: Major damage to thatched houses / huts. Roof tops may blow
off. Unattached metal sheets may fly.
Communication and power: Minor damage to power and
communication lines.
Road/Rail: Major damage to Kutcha and some damage to Pucca roads.
Flooding of escape routes.
Agriculture: Breaking of tree branches, uprooting of large avenue trees.
Moderate
damage to Banana and Papaya trees: Large dead limbs blown from trees.
Marine
Interests:
Phenomenal seas with wave height 9-14 m. Movement in motor boats unsafe.
Coastal
Zone: Major damage
to coastal crops. Storm surge upto 1.5m (area specific) causing damage to
embankments/ salt pans. Inundation upto 5 Km in specific areas.
Overall
Damage Category: Moderate
Suggested
Actions: Fishermen
advised not to venture into sea. Coastal hutment dwellers advised to move to
safer places. Other people in the affected areas to remain indoors.
What is the
damage potential of a very severe cyclonic storm (64-90 Knots
or 118-167 Kmph) and what are the suggested
actions?
Structures: Total destruction of thatched houses/ extensive damage to
Kutcha houses. Some damage to Pucca houses. Potential threat from flying
objects.
Communication and power: Bending/
uprooting of power and communication poles.
Road/Rail: Major damage to Kutcha and Pucca roads. Flooding of escape
routes. Minor disruption of railways, overhead power lines and signaling
systems.
Agriculture: Widespread damage to standing crops plantations, orchards,
falling of green coconuts and tearing of palm fronds Blowing down bushy trees
like mango.
Marine
Interests:
Phenomenal seas with wave heights more than 14m. Visibility severely affected.
Movement in motor boats and small ships unsafe.
Coastal
Zone: Storm surge
up to 2 m, Inundation up to 10 Km in specific areas. Small boats, country crafts
may get detached from moorings.
Overall Damage Category:
Large
Suggested
Actions: Fishermen
not to venture into sea. Evacuation from coastal areas needs to be mobilized.
People advised to remain indoors. Judicious regulation of rail and road traffic
needed.
What is the
damage potential of a very severe cyclonic storm (91-119 Knots
or 168-221 Kmph) and what are the suggested actions?
Structures: Extensive damage to all types Kutcha houses, some damage to
old badly managed Pucca structures. Potential threat from flying
objects.
Communication and power: Extensive uprooting of power and
communication poles.
Road/Rail: Disruption of rail / road link at several places.
Agriculture: Extensive damage to standing crops plantations, orchards.
Blowing down of Palm and Coconut trees. Uprooting of large bushy trees.
Marine
Interests:
Phenomenal seas with wave heights more than 14m. Movement in motor boats and
small ships not advisable.
Coastal
Zone: Storm surge
up to 2 – 5 m, Inundation may extend up to 10-15 Km over specific areas. Large
boats and ships may get torn from their moorings, country crafts may get
detached from moorings
Overall
Damage Category:
Extensive
Suggested
Actions: Fishermen
not to venture into sea. Evacuation from coastal areas essential. Diversion /
suspension of rail traffic may be required.
What is the
damage potential of a super cyclonic storm 120 Knots (222
Kmph) & above? What are the suggested
actions?
Structures: Extensive damage to non-concrete residential and industrial
building. Structural damage to concrete structures. Air full of large
projectiles.
Communication and power: Uprooting
of power and communication poles. Total disruption of communication and power
supply.
Road/Rail: Extensive damage to Kutcha roads and some damage to poorly
repaired pucca roads. Large scale submerging of coastal roads due to flooding
and sea water inundation. Total disruption of railway and road traffic due to
major damages to bridges, signals and railway tracks. Washing away of rail /
road links at several places.
Agriculture: Total destruction of standing crops / orchards, uprooting
of large trees and blowing away of palm and coconut crowns, stripping of tree
barks.
Marine
Interests:
Phenomenal seas with wave heights more than 14m. All shipping activity unsafe.
Coastal
Zone: Extensive
damage to port installations. Storm surge more than 5m, Inundation up to 40 Km
in specific areas and extensive beach erosion. All ships torn from their
moorings. Flooding of escape routes.
Overall Damage Category:
Catastrophic
Suggested
Actions: Fishermen
not to venture into sea. Large scale evacuations needed. Total stoppage of rail
and road traffic needed in vulnerable areas.
What is the
normal movement of a Tropical Cyclone?
Tropical
Cyclones move as a whole. They casually move west-northwestwards or
northwestwards in the northern hemisphere. The average speed is 15-20 kmph
(360-480 km per day). They may change their direction of movement towards north.
During this change their speed of movement decreases to 10 kmph or even less. A
larger fraction of such storms later turn towards northeast and move
northeastwards very fast at a speed of 25 kmph or more.
What are
fast and slow moving cyclones?
When the
speed of movement is 10-14 kmph, it is called as slow moving cyclone. It is
called as moderately moving cyclone, if the speed of movement is 15-25 kmph. If
the speed of movement is more than 25 kmph, is called as fast moving
cyclone.
How track prediction is done in IMD
?
Various Techniques are available
for Track Prediction of the storm as mentioned below:
-
Methods
based on climatology, persistence and both Climatology & Persistence
(CLIPER)
-
Synoptic Techniques – Empirical Techniques
-
Satellite Techniques
-
Statistical Techniques using climatology, persistence and
synoptic
-
Analogue Techniques
-
Numerical weather prediction models
The
tracks of the cyclonic storms over north India ocean during 1891-2007 are shown
below:
What are the numerical weather prediction models used
operationally for Tropical Cyclone track Prediction and storm surges in
IMD?
-
T-254
model of NCMRWF, MM5 mesoscale model
-
Quasi-Lagrangian Limited Area Model (QLM) for track
prediction
-
Weather
Research and Forecast (WRF) mesoscale model for intensification and track
prediction
-
Prediction Models of IIT – Delhi and NIOT Chennai for
Storm Surge rediction
In
addition to above, IMD forecasters make use of various forecasts available from
international NWP models like BCBCMRF, UKMET and COLA etc.
What is our accuracy of landfall prediction?
Probability of correct forecast decreases with increasing
forecast validity period. Mean forecast errors for 12, 24, 48 and 72 hours are
about 50, 140, 300 and 500 km respectively, which are comparable to
corresponding figures of other centres like National Hurricane Centre, Miami,
which monitor Atlantic Hurricanes; Typhoon Warning Centre, Tokyo, which monitors
Typhoons of Northwest Pacific etc.
How does IMD
predict intensity of the cyclone ?
Subjective techniques like Climatology, Synoptic and
Satellite (Dvorak) techniques and radar techniques are used. Though the
performance of NWP models in intensity prediction is not satisfactory, they
provide valuable guidance in intensity prediction also.
What is the
role of upper tropospheric westerly trough ?
An
Upper tropospheric westerly
trough is important for tropical cyclone
forecasting as they can force large amounts of vertical wind shear over tropical
disturbances and tropical cyclones which may inhibit their strengthening. There
are also suggestions that these troughs can assist tropical cyclone genesis and
intensification by providing additional forced ascent near the storm centre
and/or by allowing for an efficient outflow channel in the upper troposphere.
The location of this trough and its intensity can also influence the movement of
the storm and hence can be used for cyclone track forecasting.
Why Tropical
Cyclones weaken over land after landfall ?
After just a few hours, a tropical
cyclone over land begins to weaken rapidly because the storm lacks the moisture
and heat sources that the ocean provided. This depletion of moisture and heat
hurts the tropical cyclone's ability to produce thunderstorms near the storm
centre. Without this convection the cyclone cannot survive.
However,
there are instances like Orissa super cyclone of October 1999, which maintained
its intensity of cyclonic storm even 24 hours after landfall. During this
period, it remained practically stationary over coastal Orissa.
Doesn't the
friction over land kill tropical cyclones?
No,
during landfall, the increased friction over land acts - somewhat contradictory
- to both decrease the sustained winds and also to increase the gusts felt at
the surface. The sustained winds are reduced because of the dampening effect of
larger roughness over land (i.e. bushes, trees and houses over land versus a
relatively smooth ocean). The gusts are stronger because turbulence increases
and acts to bring faster winds down to the surface in short (a few seconds)
bursts.
What are the abnormal characteristics associated with
Tropical Cyclones?
Majority
of Tropical Cyclones are associated with some sort of abnormal behavior such
as
-
Rapidly
changing trends in motion and intensity
-
Remaining quasi-stationary close to landfall
-
Development or intensification close to a populated
coastline
-
Approaching a vulnerable coastline at an acute angle so
that even minor forecast errors introduce large landfall
uncertainties
-
Threatening the coastal community during high pitch of
seasonal activity such as harvesting, festivals, holidays
etc.
Two
examples of such cyclones are shown below.
What is the organizational set up in IMD for Cyclone
forecasting and Warning?
The
Cyclone Warning Organization in India has a 3-tier system to cater to the needs
of the maritime States. These are : Cyclone Warning Division set up at IMD Head
Quarters to co-ordinate and supervise cyclone warning operations in the country
and to advise the Govt. at the apex level; Area Cyclone Warning Centres at
Chennai, Mumbai and Kolkata and Cyclone Warning Centres at Visakhapatnam,
Ahmedabad and Bhubaneswar. The cyclone warning work is also supervised and
coordinated by the Forecasting Division at Pune.
What are the different bulletins issued by IMD in connection
with the cyclone?
-
Weather and Sea area bulletins.
-
Bulletins for Indian Navy.
-
Bulletins for Departmental Exchange.
-
Port Warnings
-
Fisheries warnings
-
Four Stage Warnings
-
Bulletins for AIR
-
Bulletins for Press
-
Coastal bulletins
-
Warnings to Designated/ Registered Officials
-
Aviation Warnings
What is 4-stage warning system for Tropical
Cyclones?
Expectations of Disaster Managers are longer lead time and
improved accuracy of landfall forecast. But the present state of art has
limitations to make the above requirements go hand in hand. Lead time depends on
the formation and duration of cyclone itself which may vary considerably from
one cyclone to another. However, since pre-monsoon cyclone season of 1999, IMD
introduced a 4-Stage warning system to issue cyclone warnings to the disaster
managers. They are as follows:
(1) Pre-Cyclone
Watch
Issued
when a depression forms over the Bay of Bengal irrespective of its distance from
the coast and is likely to affect Indian coast in future. The pre-cyclone watch
is issued by the name of Director General of Meteorology and is issued at least
72 hours in advance of the commencement of adverse weather. It is issued at
least once a day.
(2) Cyclone Alert
Issued
atleast 48 hours before the commencement of the bad weather when the cyclone is
located beyond 500 Km from the coast. It is issued every three hours.
(3)
Cyclone Warning
Issued at
least 24 hours before the commencement of the bad weather when the cyclone is
located within 500 Km from the coast. Information about time /place of landfall
are indicated in the bulletin. Confidence in estimation increases as the cyclone
comes closer to the coast
(4)
Post landfall outlook
It is
issued 12 hours before the cyclone landfall, when the cyclone is located within
200 Km from the coast. More accurate & specific information about time
/place of landfall and associated bad weather indicated in the bulletin. In
addition, the interior distraction is likely to be affected due to the cyclone
are warned in this bulletin.
How frequently IMD issues these bulletins?
When
cyclone is beyond the range of coastal cyclone detection radar, (more than 400
km away from coast), cyclone warnings are issued 6 times a day to air stations
and each warning is broadcast at frequent intervals interrupting routine
programme. When the cyclone comes within radar range and tracked by radar,
cyclone warnings are issued every hour to air stations. During cyclone period,
concerned air stations keep round the clock watch for broadcasting cyclone
warnings.
Is there any order in mentioning the disastrous weather in
the bulletin?
A certain order depending upon the
intensity and proximity of the system to the coast will be observed during
cyclone period while indicating the adverse weather.
In case
of a cyclone expected to strike the coast in
-
About 12 hrs: tidal wave / gales / heavy rain
fall
-
Next 12-24 hrs: gales / tidal wave / heavy rain
fall
-
About 24 hrs: rain / gales / tidal wave
The
strong winds and high seas pose dangers to port. Moreover if a storm is at high
seas the ships moving out of the port may fall into danger. Therefore the port
is informed accordingly and advised to hoist signals which can he seen by
mariners both during day and night. There are eleven such signals. The
significant features of this warning are as follows.
-
Port officers are warned about disturbed weather likely to
affect their Ports by IMD.
-
On receipt of warnings, Port officials hoist appropriate
visual signals so that they are visible from a distance.
-
Ports are warned 5 to 6 times a day during period of
cyclonic storm.
-
Warning contains information about location, intensity,
expected direction, expected landfall point and type of signal the Port should
hoist.
-
Uniform system of storm warning signals introduced from
1st April 1898.
There are different types of signals for different ports as
mentioned below.
-
GENERAL SYSTEM : General Ports (eleven
signals)
-
EXTENDED SYSTEM: Extended Ports (Six section signals +
eleven signals)
-
BRIEF SYSTEM : Brief ports (III, IV, VII, X, XI
signals)
-
MINOR PORTS : Special messages. No signals are
hoisted.
PORT WARNINGS
|
Signal/ Flag No.
|
|
NAME
|
Symbols
|
Description
|
|
Day
|
Night
|
|
1.
|
Distant bad
weather
|
DC1
|
|
|
Depression far at sea. Port NOT
affected.
|
|
2.
|
DW2
|
|
|
Cyclone for at
sea.
Warning for vessels leaving
port.
|
|
3.
|
Local
bad weather
|
LC3
|
|
|
Port Threatened by local bad
weather like squally winds.
|
|
4.
|
|
LW4
|
|
|
Cyclone at sea. Likely to affect the port
later.
|
|
5.
|
Danger
|
D5
|
|
|
Cyclone likely to cross coast
keeping port to its left
|
|
6.
|
|
D6
|
|
|
Cyclone likely to cross coast
keeping port to its right.
|
|
7.
|
|
D7
|
|
|
Cyclone likely to cross coast
over/near to the port.
|
|
8.
|
Great
danger
|
GD8
|
|
|
Severe
cyclone to cross coast keeping port to its
left
|
|
9.
|
GD9
|
|
|
Severe cyclone to cross coast keeping port to its
right
|
|
10.
|
GD10
|
|
|
Severe cyclone to cross coast
keeping port to its right.
|
|
11.
|
XI
|
|
|
Communication failed with cyclone warning
office.
|
W
hat are fishermen warning?
A
fisherman warning is warning message for fishermen who ply on coastal areas or
may go out at sea. Dangers to fisherman due to storm are strong winds and
associated high seas, due to which fishing boats may capsize. Hence,
the fishermen are
issued warning when one of the following conditions of weather is expected along
and off any coast
-
Strong off-shore and on-shore winds (or with appropriate
direction), speed exceeding 45 kmph
-
Squally weather – frequent squalls with rain; or
persistent type of strong gusty winds (>20kts; 36kmph) accompanied by rain.
-
Gales and
-
State of sea very rough or above (wave heights are four metres or
more).
The
warnings are disseminated to fishermen through
-
Port
-
Fisheries officials and
-
AIR
broadcast daily three / four times in local language. The warnings are
broadcast as a routine four times a day (morning (0600 hrs), mid-day, evening
(1800 hrs) and mid-night) from the air stations in the local language. During
a cyclonic storm, such warnings are covered in the cyclone bulletins sent to
the air stations at hourly or 3 hourly intervals for frequent broadcast. The
fisheries warnings issued in mid-day are incorporated in the ‘general weather
bulletin’ by forecasting offices in maritime states.
The
fishermen warning contains information about
-
Synoptic situation
-
Signals hoisted and
-
Advice not to go out in to the sea.
What is sea
area bulletin?
-
Issued by ACWC for deep
sea
-
Normally twice a day (based on 03
and 12 UTC
-
Thrice a day in case of
depression/ deep depression (additional bulletin based on 18 UTC)
-
Six times a day in case of a
cyclone. There is also provision of special bulletin.
-
The bulletin contains significant
system, expected weather, wind, state of sea, port warning
etc.
What is coastal weather bulletin?
-
Issued by area cyclone warning
centre/ cyclone warning centre for coastal shipping
-
Normally twice a day (based on 03
and 12 UTC
-
Issued based on sea area
bulletin
-
Thrice a day in case of
depression/ deep depression (additional bulletin based on 18 UTC)
-
Six times a day in case of a
cyclone. There is also provision of special bulletin
-
The bulletin contains significant
system, expected weather, wind, state of sea, port warning etc
What is the meaning of widespread /fairly wide
spread/scattered/isolated rainfall?
The
rainfall distribution as mentioned in the bulletin are based on following
classification
|
DISTRIBUTION
|
NO. OF PLACES
|
DESCRIPTION
|
|
Isolated
|
One or two places
|
<25% of area gets rainfall
|
|
Scattered
|
A few places
|
(26 –50)% of area gets rainfall
|
|
Fairly Widespread
|
A many places
|
(51 – 75)% of area gets rainfall
|
|
Wide Spread
|
Most place
|
(76 – 100)% of area gets
rainfall
|
What do you
mean by heavy rainfall, very heavy rainfall and extremely heavy rainfall
?
The intensity of rainfall mentioned
in the bulletin is based on the following criteria:
|
Descriptive term used
|
Rainfall amount in mm
|
|
No rain
|
0.0
|
|
Very light rain
|
0.1- 2.4
|
|
Light rain
|
2.5 – 7.5
|
|
Moderate rain
|
7.6 – 35.5
|
|
Rather heavy
|
35.6 – 64.4
|
|
Heavy rain
|
64.5 – 124.4
|
|
Very heavy rain
|
124.5 –
244.4
|
|
Extremely heavy
rain
|
>244.5
|
|
Exceptionally heavy rain
|
When the amount is a value near about highest recorded
rainfall at or near the station for the month or season. However, this
term will be used only when the actual rainfall amount exceeds 12
cm.
|
How does IMD
mention state of sea in the bulletins?
This is mentioned subjectively in
plain language like rough sea, very rough sea etc. based on the prevailing wind
over the sea surface as mentioned below.
|
Descriptive Term
|
Height
Metres
|
Wind Speed
Knots (Kmph)
|
Inbeaufort
Scale
|
|
CALM (GLASSY)
|
0
|
0
|
0
|
|
CALM (RIPPLED)
|
0 - 0.1
|
1 - 3 (2 - 6)
|
1
|
|
SMOOTH
(WAVELESS)
|
0.1 - 0.5
|
4 - 10 (7 - 19)
|
2 - 3
|
|
SLIGHT
|
0.5 - 1.25
|
11 - 16 (20 - 30)
|
4
|
|
MODERATE
|
1.25 - 2.5
|
17 - 21 (31 - 39)
|
5
|
|
ROUGH
|
2.5 - 4.0
|
22 - 27 (41 - 50)
|
6
|
|
VERY ROUGH
|
4.0 - 6.0
|
28 - 33 (52 - 61)
|
7
|
|
HIGH
|
6.0 - 9.0
|
34 - 40 (63 - 74)
|
8
|
|
VERY HIGH
|
9.0 - 14.0
|
41 - 63 (76 -
117)
|
9 - 11
|
|
PHENOMENAL
|
OVER 14
|
64 OR ABOVE
(119 OR ABOVE)
|
12
|
What is
meaning of the reference time mentioned in the bulletin ?
The meaning of different reference
times mentioned in the bulletin are given below.
-
EARLY HOURS 0000 - 0400 HRS. IST
-
MORNING 0400 - 0800 HRS. IST
-
FORENOON 0800 - 1200 HRS. IST
-
AFTERNOON 1200 - 1600 HRS. IST
-
EVENING 1600 - 2000 HRS. IST
-
NIGHT 2000 - 2400 HRS. IST
-
EARLY MORNING 0400 - 0600 HRS. IST
-
AROUNDNOON 1100 - 1300 HRS. IST)
How are Cyclone Warnings disseminated ?
The different telecommunication channels used are as
follows
However,
the Telex is being phased out by Department of Telecommunications, Govt. of
India.
What are the bulletins available in the website? What is the
website address ?
There are
two cyclone related bulletins issued by Cyclone Warning Division, IMD, New
Delhi. These are as follows.
-
Bulletin for Indian coast
-
Regional Specialised Meteorological Centre (RSMC)
bulletin
In,
addition, the predicted track of the cyclone based on quasi-Lagrangian model
(QLM) run by IMD. All these information/bulletins are available in the Cyclone
Page of IMD’s Web site (www.imd.gov.in)
What is IVRS ? How does it work ?
IVRS
stands for interactive voice response system. The requests for weather
information and forecasts from the general public are automatically answered by
this system. For this purpose, the person has to dial a toll-free Number
“18001801717” from anywhere in the country. This system has been installed at 26
Meteorological Centres/ Regional Meteorological Centres. The data on maximum
& minimum temperatures and Rainfall for a large number of towns/cities are
provided. The local weather forecasts of cities and multi-hazard warnings
including cyclone warnings are also provided.
What is
Cyclone Warning Dissemination System (CWDS)?
This is a
unique scheme not tried anywhere in the world. The scheme has been extremely
successful during the cyclones for last 24 years and gained considerable
confidence of the public of this country.
-
Designed by ISRO and implemented by IMD in the
mid-eighties, the CWDS is used all these years to disseminate cyclone warnings
effectively.
-
Selective addressing (Separate messages for each district)
is done by transmitting a digital code followed by the actual warning
message
-
Cyclone
warnings are generated in English and other local languages (Tamil, Telugu,
Oriya, Bengali, Marathi, Gujarathi etc)
-
Though
Radio/TV broadcast are for one and all, the messages through CWDS can be
accessed only at centres equipped with a receiver and addressed specifically
for receiving the message
-
CWDS is
one-way communication system and will be complimentary to other systems of
cyclone warning dissemination. Facility of acknowledgement is available in the
upgraded (Digital) version of CWDS
-
The
present CWDS network covers 252 stations spread over coastal areas of maritime
districts along the east and e west coast
-
Through
World Bank assistance Govt. of Andhra Pradesh had installed 100 Digital CWDS
receivers along Andhra Coast. For this purpose a digital up-linking station
also functions at Chennai.
Who are the
recipients of Cyclone Warnings?
Warnings
are issued for general public, fishermen, farmers and different categories of
users such as central and state government officials responsible for disaster
mitigation and relief, industrial and other establishments located in the
coastal areas, ports, coastal shipping, railways, aviation, transport,
communication and power authorities.
How a common man gets information about a cyclonic
storm?
Local AIR
broadcast hourly (or more frequently) bulletins in local language as well as in
Hindi and English. The bulletins give the location of the Cyclonic storm, its
direction of movement, place and time of landfall and details of adverse weather
expected over the areas likely to be affected by the storm. AIR, New Delhi
issues bulletins thrice in a day giving similar information. Apart from that,
the cyclone warning messages are sent to the collectors of the districts likely
to be affected and the chief secretary of concerned state. The state Govt. takes
necessary steps to inform the local population through their machinery such as
police wireless etc. They make necessary arrangement for evacuation from coastal
area and for removal of the population to other places.
On the event of any doubt about approach of a cyclonic storm
to whom a common man can approach to get authentic information (in absence of
relevant AIR bulletins)?
Normally
all collectors of coastal districts (subjected to adverse weather due to
cyclonic storm) are intimated by sending warning messages through fax. They in
turn inform junior officers under their control to take necessary action. These
informations will be therefore available with the state Govt. officials. More
over if any one is having phone facilities he may contact nearest cyclone
warning centre/ Area cyclone warning centre or Cyclone Warning Division at IMD
Head Quarters, New Delhi to get most authentic information about storms over Bay
of Bengal. Also one can take advantage of IVRS system to get latest
information.
How does IMD keep liaison with State
officials?
Area
Cyclone Warning Centres (ACWCs) and Cyclone Warning Centres (CWCs) maintain
liaison with the concerned state Governments in state and district levels on
cyclone related activities. The cyclone warning bulletins are communicated to
the Chief Secretary, Revenue Secretary, Special Relief Commissioner, State
control room, State Disaster Management Authority and concerned district
collectors every three hourly. In addition, the Chief Secretary is personally
briefed by Director, ACWC/CWC regularly. Before the cyclone season, ACWC/CWC
organizes the precyclone preparedness meeting under the chairmanship of Chief
Secretary where all the high state Govt. officials from various departments
participate.
What are the devastations which can not be protected by a
common man and has to be mentally prepared to accept the loss?
Inundations caused by storm surge, uprooting of trees and
damage caused by that, flooding of low lying areas due to heavy rain and damage
to houses and communication due to very strong winds.
How to understand that the cyclonic storm has weakened/moved
away?
With the
approach of a storm squally weather commences. On the other land the storm
weakens or goes away from the station the /weather gradually improves. The
rainfall decreases. the wind speed weakens and gradually sky clears. However one
should be very careful about the situation when the centre of the storm
technically known as the "eye" of the storm passes through the station. The
station will first experience very severe weather with approaching cyclone. When
the eye of the storm passes over the station the weather becomes practically
fair with light winds and little or no clouds at all. During night stars may he
visible. But after a lapse of few minutes (say 10-15 minutes) very severe
weather again commences. This time the wind blows from exactly the opposite
direction. A sharp change from very severe weather to fair weather may be an
indication that the eye of the storm is approaching the station.
What are the pre-cyclone/during the cyclone/post cyclone
responsibilities of a common man?
1. Steps to be
taken before the cyclone
-
Check
houses, secure loose tiles by cementing wherever necessary, repair doors and
windows.
-
Check
the area around the house -remove dead or dying trees, anchor removable
objects like lumber piles, loose bricks, garbage cans, sign-boards, loose zinc
sheets etc.
-
Keep
some wooden boards ready so that glass windows can be
boarded.
-
Keep a
hurricane Lantern filled with kerosene, flash light and enough dry
cells.
-
Promptly demolish condemned buildings.
-
Those
who have radio sets should ensure that the radio is fully serviceable in the
case of transistors an extra set of batteries should be kept
handy.
2. Steps to be
taken during the cyclone.
-
Keep
your radio on and listen to latest weather warnings and advisories from the
nearest All India Radio station. Pass the information to
others.
-
Avoid
being misled by rumors. Pass only the. Official information you have got from
the radio to others.
-
Get
away from low lying beaches or other locations which may be swept by high
tides or storm waves. Leave sufficiently early before your way to high ground
gets flooded. Do not delay and run the risk of being
marooned.
-
If your
house is out of danger from high tides and flooding from the river, and it is
well built, it is then probably the best place during weather and storm.
However, please act promptly if asked to evacuate.
-
Be
alert for high water in areas where streams of rivers may flood due to heavy
rains.
-
Board
up glass windows or put storm shutters in place. Use good wooden planks
Securely fastened. Make-shift boarding may do more damage than none at all.
Provide strong suitable support for outside doors.
-
If you
do not have wooden boards handy paste paper strips on glasses to prevent
splinters flying into the, house.
-
Get
extra food, specially things which can be eaten without cooking or with very
little preparation. Store extra drinking water in suitable covered
vessel.
-
If you
are in one of the evacuation areas, move your valuable articles to upper
floors to minimise flood damage.
-
Have
hurricane lantern, flash lights and/or other emergency light in working
condition and keep them handy.
-
Check
on everything that might blow away or be torn loose. Kerosene tins, cans,
agricultural implements, garden tools, road signs and other objects become
weapon of destruction in strong winds. Remove them and store them in a covered
room.
-
Be Sure
that a window or door can be opened on the lee side of the house i.e. the side
opposite the one facing the wind.
-
Make
provisions for children and adults requiring special diets.
-
If the
centre of' ‘eye' of the storm passes directly over your place, there will be a
lull in the wind and rain, lasting for half an hour or more. During this
period stay in safe place. Make emergency repairs during the lull period if
necessary, but remember that strong wind will return suddenly from the
opposite direction, frequently with even greater violence.
(xv) Be
calm. Your ability to meet emergency will inspire and help others.
3. Steps to be
taken after Cyclone.
-
They
should remain in shelters until informed by those in charge that they may
return home.
-
Any
loose and dangling wire from the lamp post should be strictly
avoided.
-
People
should keep away from disaster areas unless they are required to
assist.
-
Anti-social elements should be prevented from doing
mischief and reported to the police.
-
Cars,
buses lorries and carts should be driven carefully.
-
The
houses and dwellings should be cleared of debris.
-
The
losses should be reported to the appropriate authorities.
-
Relatives should be promptly informed about the safety of
persons in the disaster area.
How IMD
coordinates with National Disaster Management Division (NDM) of the Ministry of
Home Affairs?
IMD has
established linkages/institutional arrangements with disaster management
agencies both at the centre and in the states. During normal weather conditions
two bulletins are transmitted to Control Room of National Disaster Management
Division (NDM). In a case of depression develops over north Indian Ocean which
has the potential to affect Indian coast, special bulletins at-least three times
a day are issued to NDM. When the system intensifies into a cyclonic storm, the
cyclone warning bulletins are every three hourly. At present 4 stage warning
procedure as discussed earlier is followed for issuing bulletins to NDM Control
Room. When the system weakens or not going to affect Indian coast, a dewarning
message is also issued to NDM Control Room. The cyclone warning bulletins are also passed on to State
Government Authorities/District Collectors who are in constant touch with
Cyclone Warning Centres. The centres and local committees consisting of various
departments dealing with disaster management issues meet at the time of crisis
and take necessary follow up actions.
What is the
role of IMD Tropical Cyclone management of north Indian Ocean Rim
countries?
A
Regional Specialized Meteorological Centre (RSMC) has been established at IMD,
New Delhi. It is one of the six such centres recognized by the WMO under a
global system for monitoring tropical cyclones. As an international commitment,
through the WMO/ESCAP Panel on Tropical Cyclones, tropical cyclone advisories
are issued by RSMC, New Delhi to the Panel Member countries during the tropical
cyclones in the Bay of Bengal and the Arabian Sea. The other ESCAP Panel
countries are Thailand, Myanmar, Bangladesh, Pakistan, Sri Lanka, Maldives and
Oman.
What are the bulletins issued by RSMC, New
Delhi?
RSMC New
Delhi issues the following bulletins
-
Tropical Weather Outlook for WMO/ESCAP Panel member
countries
-
Special Tropical Weather Outlook for WMO/ESCAP Panel
member countries
-
Tropical Cyclone Advisory for Panel member
countries
-
Tropical Cyclone Advisory for International
Aviation
RSMC, New
Delhi is also designated as Tropical Cyclone Advisory Centre (TCAC) and issues
cyclone advisories for International Aviation as per the guidelines of ICAO.
These advisories are issued every six hours based on observations at 0000, 0600,
1200 and 1800 UTC.
What is UTC?
How do I tell at what time a satellite picture was taken?
UTC stands for Universal Time
Coordinated, what
used to be called Greenwich Mean Time (GMT) and Zulu Time (Z). This is the time at the Prime Meridian (0° Longitude)
given in hours and minutes on a 24 hour clock. For example, 0000 UTC is 0530
hours IST. The Greenwich Royal Observatory at Greenwich, England (at 0°
Longitude) was where naval chronometers (clocks) were set, a critical instrument
for calculating longitude. This is why GMT became the standard for world
time. Meteorologists have used UTC or GMT times for over a century to ensure that observations taken
around the globe are taken simultaneously.
On most
satellite pictures and radar images the time will be given as UTC, GMT, or Z time.
What is
relation between kmph and knots (or m/s) ?
For winds:
1 mile per hour = 0.869 international
nautical mile per hour (knot)
1 knot = 1.852 kilometers per hour
1 knot = 0.5144 meter per second
1 meter per second = 3.6 kilometers per
hour
Why are
tropical cyclones named?
Tropical
cyclones are named to provide easy communication between forecasters and the
general public regarding forecasts, watches, and warnings. Since the storms can
often last a week or longer and that more than one can be occurring in the same
basin at the same time, names can reduce the confusion about what storm is being
described. The first use of a proper name for a tropical cyclone was by an
Australian forecaster early in the 20th century. He gave tropical cyclone names
"after political figures whom he disliked. By properly naming a hurricane, the
weatherman could publicly describe a politician (who perhaps was not too
generous with weather-bureau appropriations) as 'causing great distress' or
'wandering aimlessly about the Pacific.'" (Perhaps this should be brought back
into use)
During
World War II, tropical cyclones were informally given women's names by US Army
Air Corp and Navy meteorologists (after their girlfriends or wives) who were
monitoring and forecasting tropical cyclones over the Pacific. From 1950 to
1952, tropical cyclones of the North Atlantic Ocean were identified by the
phonetic alphabet (Able-Baker-Charlie-etc.), but in 1953 the US Weather Bureau
switched to women's names. In 1979, the WMO and the US National Weather Service
(NWS) switched to a list of names that also included men's names.
The
Northeast Pacific basin tropical cyclones were named using women's names
starting in 1959 for storms near Hawaii and in 1960 for the remainder of the
Northeast Pacific basin. In 1978, both men's and women's names were
utilized.
The
Northwest Pacific basin tropical cyclones were given women's names officially
starting in 1945 and men's names were also included beginning in 1979. Beginning
on 1 January 2000, tropical cyclones in the Northwest Pacific basin are being
named from a new and very different list of names. The new names are Asian names
and were contributed by all the nations and territories that are members of the
WMO's Typhoon Committee. These newly selected names have two major differences
from the rest of the world's tropical cyclone name rosters. One, the names by
and large are not personal names. There are a few men's and women's names, but
the majority are names of flowers, animals, birds, trees, or even foods, etc,
while some are descriptive adjectives. Secondly, the names will not be allotted
in alphabetical order, but are arranged by contributing nation with the
countries being alphabetized.
The
Southwest Indian Ocean tropical cyclones were first named during the 1960/1961
season.
The
Australian and South Pacific region (east of 90E, south of the equator) started
giving women's names to the storms in 1964 and both men's and women's names in
1974/1975.
The North
Indian Ocean region tropical cyclones are being named since October 2004. The
list of approved names of the cyclones over north Indian Ocean is given
below:
List of approved names of tropical
cyclones over the north Indian Ocean
|
WMO/ESCAP Panel
Member contributing the names
|
Column one
|
Column two
|
Column three
|
Column four
|
|
Names
|
Pron’
|
Names
|
Pron’
|
Names
|
Pron’
|
Names
|
Pron’
|
B’desh
|
Onil
|
Onil
|
Ogni
|
Og-ni
|
Nisha
|
Ni-sha
|
Giri
|
Gi-ri
|
|
India
|
Agni
|
Ag’ni
|
Akash
|
Aakaa’sh
|
Bijli
|
Bij’li
|
Jal
|
Jal
|
|
Maldives
|
Hibaru
|
--
|
Gonu
|
--
|
Aila
|
--
|
Keila
|
--
|
|
Myanmar
|
Pyarr
|
Pyarr
|
Yemyin
|
Ye-myin
|
Phyan
|
Phyan
|
Thane
|
Thane
|
|
Oman
|
Baaz
|
Ba-az
|
Sidr
|
Sidr’
|
Ward
|
War’d
|
Murjan
|
Mur’jaan
|
|
Pakistan
|
Fanoos
|
Fanoos
|
Nargis
|
Nar
gis
|
Laila
|
Lai
la
|
Nilam
|
Ni
lam
|
|
Sri
Lanka
|
Mala
|
--
|
Rashmi
|
Rash’mi
|
Bandu
|
--
|
Mahasen
|
--
|
|
Thailand
|
Mukda
|
Muuk-dar
|
Khai
Muk
|
Ki-muuk
|
Phet
|
Pet
|
Phailin
|
Pi-lin
|
|
|
|
Panel
Member
|
Column five
|
Column six
|
Column seven
|
Column eight
|
|
Names
|
Pron’
|
Names
|
Pron’
|
Names
|
Pron’
|
Names
|
Pron’
|
B’desh
|
Helen
|
Helen
|
Chapala
|
Cho-po-la
|
Ockhi
|
Ok-khi
|
Fani
|
Foni
|
|
India
|
Lehar
|
Le’har
|
Megh
|
Me’gh
|
Sagar
|
Saa’gar
|
Vayu
|
Vaa’yu
|
|
Maldives
|
Madi
|
--
|
Roanu
|
--
|
Mekunu
|
--
|
Hikaa
|
--
|
|
Myanmar
|
Nanauk
|
Na-nauk
|
Kyant
|
Kyant
|
Daye
|
Da-ye
|
Kyarr
|
Kyarr
|
|
Oman
|
Hudhud
|
Hud’hud
|
Nada
|
N’nada
|
Luban
|
L’luban
|
Maha
|
M’maha
|
|
Pakistan
|
Nilofar
|
Ni
lofar
|
Vardah
|
Var
dah
|
Titli
|
Titli
|
Bulbul
|
Bul
bul
|
|
Sri
Lanka
|
Priya
|
--
|
Asiri
|
Aa’siri
|
Gigum
|
Gi’gum
|
Soba
|
--
|
|
Thailand
|
Komen
|
Goh-men
|
Mora
|
Moh-rar
|
Phethai
|
Pay-ti
|
Amphan
|
Um-pun
|
How can I
nominate a new name for the list?
The names
to be included in the list must meet some fundamental criteria. They should be
short and readily understood when broadcast. Further the names must be
culturally sensitive and not convey some unintended and potentially inflammatory
meaning. Typically, over the historical record, about one storm each year causes
so much death and destruction that its name is considered for retirement. The
suggested name may be communicated to Director General of Meteorology, India
Meteorological Department, Mausam Bhavan, Lodi Road, New Delhi-110003.
Can we tame
a tropical Cyclone to reduce its damage potential?
Considering the huge energy potential of the Cyclones, all
experiments in US under he Project “Storm Fury” to tame them have turned futile.
The best solution is not to try to alter or destroy the tropical cyclones, but
just learn to co-exist better with them. Since we know that coastal regions are
vulnerable to the storms, enforce building codes that can have houses stand up
to the force of the tropical cyclones. In this regard the Building Material
Technology Promotion Council (BMTPC), Ministry of Uraban affairs has brought out
a vulnerability map in consultation with IMD which is very useful for disaster
mamagers.
What are the
different methods tried to modified the cyclone?
-
Seeding with silver
iodide.
-
Placing a substance on the
ocean surface.
-
By nuking them.
-
By cooling the surface waters
with deep ocean water.
-
By adding a water absorbing
substance.
What are the future plans of IMD to strengthen the Cyclone
warning setup?
-
Strengthening of surface observational network with the
state-of-the-art automatic weather stations (AWSs) models.
-
A dense
network of Satellite reporting rain gauges in the coastal region.
-
Deployment of Wind Profilers and Cyclone Warning
dissemination system.
-
Increased S-Band Doppler Weather Radar network in the
coastal region
-
The up
gradation of the computing facility in IMD that will place a computing
platform capable of running high-resolution global and regional models. It
will be used for development of models for better prediction of tropical
cyclone track and intensity.
-
Augmentation of Cyclone Warning Dissemination System
(CWDS) with state-of-the-art Digital CWDS
-
Supply
of satellite radio receivers to fishermen to receive cyclone
warnings.
-
IMD
through Telecom Regulatory Authority of India (TRAI) is coordinating with
different mobile service providers including MTNL & BSNL to work out the
modalities of dissemination of disaster warning messages (Cyclone warnings)
directly to the general public who live in vulnerable
zones.
References:
Jones, S.C., Harr, P.A., Abraham,
J., Bosart, L.F., Bowyer, P.J., Evans, J.L., Hanley, D.E., Hanstrum, B.N., Hart,
R.E., Lalaurette, F., Sinclair, M.R., Smith, R.K., Thorncroft, C. 2003: The
Extratropical Transition of Tropical Cyclones: Forecast Challenges, Current
Understanding, and Future Directions. Weather and Forecasting, 18,
1052-1092.
Merrill, R. T., (1993): "Tropical
Cyclone Structure" - Chapter 2, Global Guide to Tropical Cyclone
Forecasting, WMO/TC-No. 560, Report No.
TCP-31, World Meteorological Organization; Geneva, Switzerland
Web
version of Guide
Graham,
N. E., and T. P. Barnett, 1987: Sea surface temperature, surface wind
divergence, and convection over tropical oceans. Science, No.238, pp. 657-659.
Gray,
W.M. 1979: "Hurricanes: Their formation, structure and likely role in the
tropical circulation" Meteorology Over Tropical Oceans. D. B. Shaw (Ed.), Roy.
Meteor. Soc., James Glaisher House, Grenville Place, Bracknell, Berkshire, RG12
1BX, pp.155-218
Palmen,
E. H., 1948: On the formation and structure of tropical cyclones. Geophysica , Univ. of Helsinki, Vol. 3, 1948, pp. 26-38.
Powell, M.D., S.H. Houston, and
T.A. Reinhold, 1996:"Hurricane Andrew's Landfall in South Florida, Part I:
Standardizing measurements for documentation of surface wind fields."
Wea.
Forecast. v.11, p.329-349
Hamblyn,
Richard "The Invention of Clouds: How an Amateur Meteorologist Forged the
Language of the Skies", (2001) Farrar, Straus, and Giroux New York, NY
.
DeBlieu,
Jan "Wind: How the Flow of Air Has Shaped Life, Myth, and the Land" (1998)
Houghton Mifflin Co. New York, NY
FAQ,
Joint Typhoon Warning Centre, USA
FAQ, National Hurricane Centre, USA
