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	7^th June	10^th June
2006	26^th May	30^th May
2007	28^th May	24^th May
2008	31^st May	29^th May
2009	23^rd May	26^th May
2010	31^st May	30^th May
2011	29^th May	31^st May
2012	5^th June	1^st June
2013	1^st June	3^rd June
2014	6^th June	5^th 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.