2nd Strongest Storm in Arabian Sea History: Extraordinary Chapala Hits 155 mph
By:
Jeff Masters and Bob Henson
, 4:14 PM GMT on October 30, 2015
Figure 1. Tropical Cyclone Chapala as seen by the MODIS instrument at 09:10 UTC October 30, 2015. At the time, Chapala was at peak strength with 155 mph winds. Note the large cloud of pollution at the right of the image over India. Image credit: NASA.
Figure 2. Tropical Cyclone Chapala performed its remarkable rapid intensification cycle over the warmest waters ever observed for this time of year over the Arabian Sea, as depicted in the September 2015 global climate summary from NOAA/NCEI.
Strong Arabian Sea tropical cyclones are uncommon
According to NOAA's Historical Hurricanes tool, there have only been six major Category 3 or stronger tropical cyclones recorded in the Arabian Sea (though accurate satellite records go back to just 1990.) The Arabian Sea doesn't get many tropical cyclones since it is small; furthermore, the Southwest Monsoon keeps the tropical cyclone season short, with a short season that lasts from May to early June before the monsoon arrives, then another short season in late October through November after the monsoon has departed. Strong Arabian Sea storms are rare due to high wind shear and copious dry air from the deserts of the Middle East, with just two Category 4 or 5 storms ever recorded--Gonu in 2007 and Phet in 2010. Both cyclones hit Oman after weakening below Category 4 strength. There are no recorded tropical storms to have hit Yemen, though the nation has been hit by two tropical depressions--Tropical Depression Keila in 2011, and Tropical Depression Three in 2008.
Forecast for Chapala
Recent satellite images show that Chapala degraded slightly in organization late Friday morning, and JTWC reduced the storm's estimated intensity to 150 mph winds as of 8 am EDT. However, the storm still has low wind shear, warm ocean waters near 30°C (86°F) that extend to great depth and favorable upper-level outflow. These conditions may allow the storm to intensify into a Category 5 storm by Saturday, as predicted by JTWC. Thereafter, weakening is likely as the storm encounters higher wind shear, lower oceanic heat content, and interaction with land. Chapala is likely to make landfall on Monday in a sparsely populated area in Yemen just west of the border with Oman. Hopefully, this will limit the impact on the people of Yemen, who are suffering food shortages due to war and drought. According to an October 30 article from Reuters, ten of Yemen's 22 governorates were assessed as being in an emergency food situation in June, one step below famine on a five-point scale. The assessment has not been updated since then, partly because experts have not managed to get sufficient access to survey the situation. About a third of the country's population, or 7.6 million people urgently require food aid, the The U.N. World Food Programme said (thanks go to wunderground member barbamz for alerting us to this article.)
Figure 3. The 5-day rainfall forecast from the 2 am EDT Friday, October 30, 2015 run of the HWRF model called for some truly stunning rainfall amounts in the parched desert region near the Yemen/Oman border: over two feet! Image credit: NOAA/EMC.
Figure 4. Average annual rainfall in Yemen. Image credit: CIA, via Perry-Castañeda Library Map Collection, University of Texas at Austin.
Catastrophic flooding possible with Chapala’s arrival
The latest forecasts take Chapala into the east coast of Yemen as a hurricane, and on into Saudi Arabia as a weakening tropical depression. Apart from any wind damage, this track will bring huge downpours to eastern Yemen and western Oman, where almost any amount of rainfall is an event worth noting. As shown in Figure 4, the annual average rainfall in Yemen is less than 2” along the immediate coast and less than 5” inland, except along higher terrain, where it can approach 10”. Local totals from Chapala could easily exceed 10”, with the latest run of the HWRF model predicting totals over 24" in some coastal mountainous regions. Southern Yemen was hard-hit by Tropical Depression Three of 2008, which came on the heels of heavy rains from another storm, and resulted in disastrous flooding in Yemen. According to EM-DAT, the international disaster database, that storm killed 90 people and did $400 million in damage, making it the second worst natural disaster in Yemen's history, behind a June 13, 1996 flood (thanks go to wunderground member TropicalAnalystwx13 for alerting us to this fact.) According to a report from the Global Facility for Disaster Reduction and Recovery, the 2008 cyclone dropped an average rainfall of 91 mm (3.58”) over an area of 2 million hectares (7722 square miles, or about the size of New Jersey). Losses totaled more than 6% of Yemen’s GDP, which would be the equivalent of a $1 trillion storm in the US. Although the 2008 Yemen cyclone arrived in the wake of several days of preceding rainfall, Chapala is a much stronger cyclone.
As Cyclone Gonu approached Oman back in 2007, guest blogger Margie Kieper provided this compelling description of how a storm like Chapala might affect this region.
"Imagine that you live directly on the Gulf, but in a place where it hardly ever rains, and where a hurricane has never hit, for at least a generation--for more than sixty years. Your community and many like yours are situated not only directly on the water, but near or in large dry riverbeds on the coastal plain, which is a narrow strip of sandy shoreline that is the dropoff for the three-thousand-foot mountain range behind it. Even many of the roads up into the mountains are in these dry riverbeds, which course through deep canyons as they rise into the heights. You don't have any idea what it might mean to experience winds of over 100 miles per hour, whipping up sand, and torrential rain against these mountains that can turn the riverbeds into conduits for dangerous flash floods. And you don't have any idea what storm surge is, and can't conceive of wind-driven high waves that could break against the shoreline and leave nothing behind.”
Air pollution blamed for an increase in strength of Arabian Sea tropical cyclones
Arabian Sea tropical cyclones during the pre-monsoon period in May and June have become stronger over the past 30 years owing to a reduction in vertical wind shear brought about by dimming of sunlight from air pollution particles primarily emitted in India, said Evan et al. in a 2011 paper published in the journal Nature. However, the study did not address how post-monsoon tropical cyclones in October and November, like Tropical Cyclone Chapala, might be impacted by air pollution.
Severe flash flooding in Austin/San Antonio area
A very dangerous situation was rapidly unfolding on Friday morning in and near the Hill Country of Texas, where surface low pressure was focusing repeated rounds of intense thunderstorms drawing on extremely high atmospheric moisture. At Austin's Bergstrom International Airport, where the tarmac was closed due to high water, 5.76" of rain was received in just one hour. Several CoCoRaHS stations have reported more than 10". Many roads are swamped, and high-water rescues are under way, with several counties under NWS Flash Flood Emergency status. We'll have more on this event in an upcoming post.
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