Forecast of the Onset date of Southwest Monsoon - 2015 over Kerala

Forecast of the Onset date of Southwest Monsoon - 2015 over Kerala

The southwest monsoon is likely to set over Kerala on or around 30^th May.

The onset of southwest monsoon over Kerala signals the arrival of monsoon over the Indian subcontinent and represents beginning of rainy season over the region. From 2005 onwards ESSO-India Meteorological Department (IMD) has been issuing operational forecasts for the date of monsoon onset over Kerala using an indigenously developed statistical model, which uses the following six predictors:

i) Minimum Temperature over North-west India, ii)  Pre-monsoon rainfall peak over south Peninsula, iii) Outgoing Long wave Radiation (OLR) over south China Sea, (iv) Lower tropospheric zonal wind over southeast Indian ocean, (v) upper tropospheric zonal wind over the east equatorial Indian Ocean, and (vi) Outgoing Long wave Radiation (OLR) over south-west Pacific region.

The operational forecasts for the event issued during all the last nine years (2005 to 2014) were correct as seen in the table given below.

Year	Actual Onset Date	Forecast Onset Date
2005	7th June	10th June
2006	26th May	30th May
2007	28th May	24th May
2008	31st May	29th May
2009	23rd May	26th May
2010	31st May	30th May
2011	29th May	31st May
2012	5th June	1st June
2013	1st June	3rd June
2014	6th June	5th June

Advance of southwest monsoon over the Andaman Sea normally takes place around 20^th May with a standard deviation of about one week.  During the last few days, enhanced convection and increased rainfall activity has been observed over the Bay of Bengal and the Andaman Sea.  The cross equatorial flow is likely to strengthen and deepen over the area. As such, conditions are becoming favourable for advance of southwest monsoon over the Andaman Sea and adjoining sea areas during the next 3-4 days. Past data suggests absence of any one to one association of the date of monsoon advance over Andaman Sea with the date of monsoon onset over Kerala or that with the seasonal monsoon rainfall over the country.