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. The normal monsoon onset over Kerala is 01 June. Since 2005, India Meteorological Department (IMD) has been issuing operational forecasts for the date of monsoon onset over Kerala using an indigenously developed statistical model with a model error of ± 4 days.
The southwest monsoon advances over the Andaman Sea normally around 20th May with a standard deviation of about one week. Strong convective activity has been observed over the equatorial Indian Ocean for the last several days. A well marked low pressure area has formed over the Indian Ocean which will concentrate into a depression and move north-westwards. As a result, conditions are becoming favorable for the onset of southwest monsoon over Nicobar Islands, south Andaman Sea and parts of south Bay of Bengal around 17th May and advancement over the entire Andaman Sea close to its normal date. Past data suggest that there is no association of the date of monsoon advance over the Andaman Sea either with the date of monsoon onset over Kerala or with the seasonal monsoon rainfall over the country.
The statistical model forecast suggests that the monsoon onset over Kerala in this year is likely to be slightly delayed. The southwest monsoon is likely to set over Kerala on 7th June with a model error of ± 4 days.