Southwest Monsoon Arrives Early Over Andaman Sea, Signals Potentially Rain-Rich Season Ahead

New Delhi: On Tuesday, the India Meteorological Department (IMD) confirmed the early arrival of the southwest monsoon in parts of south Bay of Bengal, south Andaman Sea, Nicobar Islands, and parts of north Andaman Sea, an early arrival.

Typically, the monsoon reaches the Andaman Sea around May 18–19. Now, it has reached the Andaman Sea almost a week ahead of its normal position of the monsoon. This early arrival followed two continuous days of widespread moderate to heavy rainfall across the Nicobar Islands indicating active monsoon conditions in the area.

Manu Singh, an environmentalist told ETV Bharat, “The anomalously early onset of the southwest monsoon over the Andaman Sea in May 2025 serves as a climatological indicator of a potentially above-normal precipitation regime for the Indian subcontinent. The fulfillment of key dynamic and thermodynamic parameters—including sustained low-level westerlies exceeding 20 knots, suppressed Outgoing Longwave Radiation (OLR) values, and persistent convective rainfall—signals a robust initiation of monsoonal circulation. This early advancement not only holds agronomic significance by potentially mitigating heat-induced crop stress but also underscores the importance of integrating mesoscale atmospheric variability into predictive agricultural and water resource planning. Nevertheless, the concurrent development of upper-air cyclonic vorticity over the Bay of Bengal necessitates heightened vigilance, as monsoon onset phases often co-occur with synoptic-scale disturbances that can modulate both rainfall distribution and intensity.”

According to the IMD, certain meteorological parameters were found to have prevailed during the preceding 48 hours to declare the advancement of the monsoon:

Persistent Rainfall Activity: Moderate to heavy showers recorded over the Nicobar Islands on an intermittent basis. Strengthening Westerly Winds: Winds at 1.5 km above mean sea level were above 20 knots and extended up to 4.5 km, indicating the deepening of monsoon currents.

Decreased Outgoing Longwave Radiation: A fall in the OLR values, which normally corresponds to increased cloudiness and convective activity, has confirmed the occurrence of the monsoon.

According to an IMD statement, “Southwest Monsoon is very likely to advance into South Andaman Sea, some parts of Southeast Bay of Bengal, and Nicobar Islands around May 13.” This would pave the way for further monsoon advancement in a few days' time, with favorable conditions having been reported over the south Arabian Sea, Maldives, and Comorin area.

Meanwhile, forecasters are now keeping an eye on a possible early onset over Kerala- the traditional entry point of the monsoon into the Indian mainland. The IMD expects the monsoon to hit Kerala on May 27, prior to its usual onset on June 1. IMD Director General Mrutyunjay Mohapatra stated last week that the monsoon's arrival and advance into the Indian subcontinent are expected to go by a normal trend this year.

This early arrival of the monsoon means some relief for those suffering in the prolonged heatwave conditions existing across various parts of India. It also aligns with IMD’s long-range forecast, which projects above-normal rainfall during the 2025 monsoon season. The southwest monsoon is crucial for India, accounting for over 70% of the country’s annual rainfall and driving the agricultural economy.

Possible Cyclonic Activity Brewing

In a related development, IMD also noted the formation of an upper air cyclonic circulation over the Andaman Sea, located between 1.5 km and 7.6 km above mean sea level and tilting southwestwards with height. While it's too early to confirm, meteorologists are closely monitoring the situation for signs of cyclone development, with some speculation about a potential system named Cyclone Shakti forming in the Bay of Bengal.

Additionally, cyclonic circulations have been observed over northwest Uttar Pradesh and West Rajasthan at lower atmospheric levels, which could influence weather patterns over northern India in the days ahead.

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