4 min readBengaluruMay 14, 2025 11:16 AM IST
First published on: May 13, 2025 at 01:09 PM IST
The India Meteorological Department (IMD) Tuesday announced the onset of the Southwest Monsoon over some areas of the Bay of Bengal and Andaman Sea at least a week before its scheduled arrival time, and said it would further advance to more parts of the country during the next three to four days.
This year’s monsoon onset over these regions is the earliest recorded in the past seven years. As per IMD’s monsoon onset schedule, the normal date for the monsoon onset over the South Andaman Sea, and Port Blair in the Andaman and Nicobar Islands is May 21.
“The Southwest Monsoon has advanced into some parts of the South Bay of Bengal, South Andaman Sea, Nicobar Islands, and some parts of the North Andaman Sea on May 13,” IMD said, adding that the monsoon advance could continue over the sea during the next three to four days.
“Conditions are favourable for further advance of Southwest Monsoon over some parts of South Arabian Sea, the Maldives and Comorin areas, some more parts of the South Bay of Bengal, entire Andaman and Nicobar Islands, remaining parts of Andaman Sea and some parts of Central Bay of Bengal during next three to four days,” said the MeT Department.
Since Monday, there has been widespread, moderate to heavy rainfall recorded over a few places over the Nicobar Islands, besides the widespread rainfall which has continued over these islands during the past two days, which is an important criterion fulfilled towards the declaration of the monsoon onset.
According to the Met department, this year’s monsoon rainfall is expected to be ‘above’ normal, quantitatively 105 per cent of the Long Period Average of 880 mm.
Mrutyunjay Mohapatra, Director General, IMD, told The Indian Express that the higher-than-normal minimum temperatures recorded over North India, the presence and strengthening of westerly winds in the lower atmospheric levels, the presence and strengthening of easterly winds over the upper atmospheric levels, early pre-monsoon rainfall accompanied by thunderstorms realised over south peninsular for about 40 days and prevailing higher-than-normal pressure over the northwest Pacific Ocean are the key factors that all indicate an early monsoon onset,
On the prevailing ocean and atmospheric conditions that may be favouring the early monsoon onset, the IMD chief said, “All these factors support the early monsoon onset over Kerala. The prevailing wind conditions indicate strengthening of monsoon winds. Both the Indian weather model and multiple other global weather models are in consensus, and suggest a heightened rainfall activity over Kerala before June 1, which is the normal onset date.”
The Southwest Monsoon is the chief rainy season for the country. Over 70 per cent of the country receives the majority of its annual rainfall during the June to September season. Every year, the monsoon winds first arrive over the Andaman Sea and the Bay of Bengal around the third week of May and further progress into mainland India.
IMD declares the monsoon onset over India when it hits Kerala, where the normal onset date is June 1. Through June and mid-July, the monsoon brings continuous rainfall before covering the entire country by around July 15. This year, the monsoon onset over Kerala is expected to be early by 5 days and would be around May 27.
Southwest monsoon onset over the South Andaman Sea and neighbourhood (2019 – 2024)
According to the Met department, this year's monsoon rainfall is expected to be 'above' normal, quantitatively 105 per cent of the Long Period Average of 880 mm. (Express Photo) 
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