India Meteorological Department (IMD) has projected that the South-West monsoon will arrive over on May 31 with a model error of +/- four days. Leading private forecaster Skymet Weather had said a couple of days ago that the onset may be precipitated by May 30 with model error of +/- two days.
The IMD’s operational forecasts of the date of monsoon onset over Kerala during the past 16 years (2005-2020) have proved to be correct except in 2015, an official spokesman said.
The monsoon sets in over Kerala normally on June 1 with a standard deviation of about seven days. The IMD has been issuing operational forecasts for the monsoon onset over Kerala from 2005 onwards.
Cylone adds strength
Explaining the developments, the IMD said that the brewing cyclone in the Arabian Sea has helped strengthen the cross-equatorial south-westerly winds which bring the monsoon to the Kerala coast.
The cross-equatorial flow is likely to strengthen and deepen over the Bay of Bengal from May 20 and sustained rainfall may be unleashed over the South Bay and the Andaman & Nicobar Islands from May 21. Hence, the monsoon advance over Andaman & Nicobar Islands may take place around May 21.
In the Indian monsoon region, initial monsoon rains materialise over the South Andaman Sea, and the monsoon winds then advance North-West across the Bay of Bengal. As per the new normal dates of monsoon onset/progress, the monsoon advances over the Andaman Sea around May 22.
However, past data suggest that there is no association of the date of monsoon advance over the Andaman Sea with either the monsoon onset over Kerala or with the seasonal monsoon rainfall over the country.