The India Meteorological Department (IMD) on Friday forecast the southwest monsoon is likely to be slightly delayed over Kerala as compared to the normal date of onset of June 1. The monsoon onset over Kerala this year is likely to be on 5th June with an error margin of four days. The model has a built-in error margin of four days – a June 5 onset can mean any day from June 1-9. Normally, southwest monsoon sets over Kerala on 1st June with a standard deviation of about 7 days.
According to IMD, initial monsoon rains are experienced over the south Andaman Sea and the monsoon winds then advance north-westwards across the Bay of Bengal. As per the new normal dates of monsoon onset/progress, the southwest monsoon advances over the Andaman Sea around 22nd May. At present, a well-marked low-pressure area lies over the southeast Bay of Bengal and neighborhood.
It is very likely to concentrate into a depression over the same region during the next 12 hours and further intensify into a Cyclonic Storm over central parts of south Bay of Bengal by Saturday evening. Associated with this event, conditions are likely to become favorable for the advance of Southwest Monsoon into the Andaman Sea, Andaman & Nicobar Islands and some parts of southeast Bay of Bengal, during the next 48 hours. Generally, the monsoon reaches Kerala within 10 days of reaching the Andamans.
However, the private weather agency Skymet has predicted that the onset date of Southwest Monsoon over Kerala this year is expected on 28th May with an error margin of +/- 2 days. Another weather agency, Weather Channel, forecast the monsoon onset date is likely to be on May 31, a day ahead of the normal onset of monsoon over Kerala.
Forecast verification for the recent 5 years (2015-2019) is given in the table below.
Year Actual Onset Date Forecast Onset Date
2015 5th June 30th May
2016 8th June 7th June
2017 30th May 30th May
2018 29th May 29th May
2019 8th June 6th June
