Monsoon reaches south Bay of Bengal, Nicobar Islands: IMD

Southwest monsoon advances over Bay of Bengal, Andaman Sea; early onset expected in Kerala, crucial for agriculture and economy.

The southwest monsoon advanced into parts of the south Bay of Bengal, south Andaman Sea, Nicobar Islands and some areas of the north Andaman Sea on Tuesday (May 13, 2025), the India Meteorological Department said.

The weather department said moderate to heavy rainfall lashed Nicobar Islands in the past two days.

The strength and depth of westerly winds over the south Bay of Bengal, Nicobar Islands and Andaman Sea increased in this period, with wind speeds exceeding 20 knots at 1.5 km above sea level and extending up to 4.5 km in some areas.

The Outgoing Longwave Radiation (OLR), an indicator of cloudiness, also decreased over the region. These conditions met the criteria for the monsoon's onset over the region, it said.

The weather office said conditions are favourable for the monsoon to advance further into more parts of the south Arabian Sea, Maldives and Comorin area; more areas of the south Bay of Bengal; the entire Andaman and Nicobar Islands; remaining parts of the Andaman Sea; and parts of the central Bay of Bengal over the next three to four days. The primary rain bearing system is likely to reach Kerala on May 27, earlier than the usual date of June 1.

If the monsoon arrives in Kerala as expected, it will be the earliest onset over the Indian mainland since 2009, when it began on May 23, according to IMD data.

Normally, the southwest monsoon makes its onset over Kerala by June 1 and covers the entire country by July 8. It starts retreating from northwest India around September 17 and withdraws completely by October 15.