2 min readBengaluruMay 8, 2026 11:38 AM IST
The Southwest Monsoon is most likely to make a timely onset over the Andaman Sea around May 20, the India Meteorological Department (IMD) said Thursday.
“The Southwest Monsoon onset is likely over parts of the South Bay of Bengal, the Andaman Sea and the Andaman and Nicobar islands towards the end of the week, May 14-20,” IMD said.
The weather bureau said southwesterly winds will prevail during the third week of May and strengthen at lower and mid-level tropospheric latitudes along the Bay of Bengal-Northeast India boundary.
As a result, IMD said, “Light to moderate intensity rainfall over a widespread area of places, with some isolated heavy to very heavy rainfall is likely over Kerala, Tamil Nadu and the south peninsular India during many days of the week, May 14 – 20.”
Many parts of southern peninsular India are already experiencing pre-monsoon showers accompanied by thunder and lightning.
This year’s monsoon is expected to unfold under the influence of developing El Niño conditions in the Pacific Ocean. In this context, IMD forecast in mid-April that rainfall across the country would be below average, at about 92 per cent of the long-period average (1971–2020).
Climatologically, the Southwest Monsoon first reaches the Andaman Sea and the Andaman and Nicobar Islands around the third week of May. As the southwest winds and the cross-equatorial flow strengthen, they gradually advance towards mainland India. The official onset over India is marked when it reaches Kerala, where the normal arrival date is June 1.
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The Southwest Monsoon is the main rainy season in India, accounting for over 70 per cent of its annual rainfall during the June to September period.
During the four-month monsoon season, India typically receives about 880 mm of rainfall.
