The southwest monsoon is likely to set in over Kerala on May 26, earlier than the normal date of June 1, the India Meteorological Department (IMD) said on Friday. The IMD said the forecast carries a model error of ± 4 days, which means the onset could occur four days before or after the projected date.

The onset over Kerala marks the beginning of the southwest monsoon season from June to September and the advance of the rain-bearing system over the Indian mainland. The monsoon reached Kerala on May 24 last year. The weather office also said conditions were favourable for the monsoon to advance over parts of the South Bay of Bengal, the Andaman Sea, and the Andaman and Nicobar Islands during the next 24 hours.

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In its forecast, the IMD said that the monsoon onset over Kerala is an important indicator of the transition from the hot and dry season to the rainy season. “As the monsoon progresses northward, relief from scorching summer temperatures is experienced over the areas,” the IMD said.

The IMD said the southwest monsoon normally sets in over Kerala on June 1, with a standard deviation of about seven days. It has been issuing operational forecasts for the date of monsoon onset over Kerala since 2005. 

The department said the model uses six predictors:

• Minimum temperatures over north-west India
• Pre-monsoon rainfall peak over the south peninsula
• Outgoing long wave radiation over the South China Sea
• Lower tropospheric zonal wind over the south-east Indian Ocean
• Outgoing long wave radiation over the south-west Pacific region
• Lower tropospheric zonal wind over the north-east Indian Ocean

The four-month monsoon season brings nearly 70 per cent of the country’s annual rainfall and is important for agriculture, the wider economy, and the recharge of reservoirs and aquifers. The IMD has also said India may receive below-normal rainfall during this year’s monsoon season, with 80 cm of rainfall likely against the long-period average of 87 cm for 1971-2020.

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The department said the expected shortfall could be linked to the emergence of El Niño conditions, which are associated with lower rainfall in India. In its monthly forecast issued on May 1, the IMD said El Niño-Southern Oscillation-neutral conditions over the equatorial Pacific were evolving towards El Niño conditions.
 

Published on: May 15, 2026 3:32 PM IST