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Informist, Friday, May 15, 2026

 

--IMD sees southwest monsoon onset over Kerala on May 26 

--CONTEXT: Normal date of monsoon onset over Kerala is around Jun 1 

 

MUMBAI – The southwest monsoon is expected to hit Kerala on May 26, with a model error of plus or minus four days, the India Meteorological Department said. This is six days before the normal date of monsoon onset over Kerala, which is around Jun. 1, with a standard deviation of about seven days, the weather department said. 

 

At present, the department uses criteria that was adopted in 2016 for declaring the onset of the monsoon over Kerala, which is based on the daily rainfall at 14 stations in Kerala and the neighbouring area, along with wind-field and outgoing long-wave radiation over the southeast Arabian Sea. If after May 10, 60% of the 14 designated stations — Minicoy and Amini in Lakshadweep, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, and Kannur in Kerala, and Kudulu and Mangalore in Karnataka – report rainfall of 2.5 millimetres or more for two consecutive days, the onset over Kerala will be declared on the second day, provided the wind-field and outgoing long-wave radiation conditions are met.

 

The outgoing long-wave radiation measures the amount of terrestrial radiation released into space and, by extension, the amount of cloud cover and water vapour that intercepts that radiation in the atmosphere. The criteria emphasise the sharp increase in rainfall over Kerala along with the setting up of large-scale monsoon flow and extension of westerlies up to 600 hectopascal. 

 

However, the department declares the monsoon onset or progress dates for other regions operationally in a subjective manner, considering the sharp increase in rainfall and its characteristic sustenance for a few days and associated changes in the atmospheric circulation features.

 

The southwest monsoon is expected to advance over the Andaman and Nicobar Islands around Saturday, nearly a week before its normal onset date of May 23 over the region, the weather department said. After the monsoon wave advances over the Bay Islands, its progression over Kerala marks its entry over the country's mainland.

 

In 2025, the southwest monsoon hit the Kerala coast on May 24, eight days ahead of its normal date of Jun. 1 and by May 29, the monsoon current covered southern and northeast India entirely, and parts of east and central India. However, after May 29, the monsoon was in a weak phase and resumed advancing only on Jun. 16. The monsoon covered entire India on Jun. 29, nine days before the normal date of Jul. 8. Normally, beginning Jun. 1, the southwest monsoon advances northwards and covers the entire country around Jul. 8.  End

 

Reported by Shreya Shetty

Edited by Avishek Dutta

 

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