Revising the forecast of the onset of the southwest monsoon over Kerala, where the weather system makes landfall on the Indian mainland, the India Meteorological Department on Tuesday (June 2, 2026) said the rainy season was now “likely to set in” around Thursday, June 4.
On May 15, the IMD predicted the onset over Kerala on May 26, with a model error of plus or minus four days.
An upper-air cyclonic circulation off the south Kerala coast is expected to aid that final push.
The IMD forecast isolated heavy to very heavy rainfall over Kerala over the next six or seven days.
IMD officials have told The Hindu that the system had stalled short of the coast rather than weakened.
Revising the forecast of the onset of the southwest monsoon over Kerala, where the weather system makes landfall on the Indian mainland, the India Meteorological Department on Tuesday (June 2, 2026) said the rainy season was now “likely to set in” around Thursday, June 4.
On May 15, the IMD predicted the onset over Kerala on May 26, with a model error of plus or minus four days. A June 4 arrival overshoots even the upper bound of that window, May 30. It is the first time since 2015 — when a May 30 forecast gave way to a June 5 onset — that the department has failed to correctly call the monsoon’s Kerala arrival. The IMD’s operational onset forecasts, which rely on a custom forecast model, had been accurate every year from 2005 to 2025 but for that one lapse.
The IMD said conditions as of Monday (June 1) “are favourable for further advance of southwest monsoon into some more parts of southwest and southeast Arabian Sea, Lakshadweep Islands, some parts of Kerala and Tamil Nadu and the Bay of Bengal around June 4”. An upper-air cyclonic circulation off the south Kerala coast is expected to aid that final push. The IMD forecast isolated heavy to very heavy rainfall over Kerala over the next six or seven days.
The IMD placed the northern limit of the monsoon — the system’s cloud promontory — along a line running from 10°N/60°E through the southern Bay of Bengal to 22°N/97°E as of Monday (June 1), with the rain yet to cross into the Kerala mainland.
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The IMD declares the monsoon’s onset over Kerala any day after May 10 when at least 60% of 14 designated stations across the State and the adjoining coast — among them Thiruvananthapuram, Kochi, Kozhikode, and Mangaluru — record 2.5 mm or more of rainfall for two consecutive days. Two further conditions must hold: westerly winds must extend up to about 600 hPa (roughly 4.5 km) over the southeast Arabian Sea, and outgoing long-wave radiation must drop below 200 W/m², a proxy for the deep cloud and convection that differentiates the monsoon from mere rain.
IMD officials have told The Hindu that the system had stalled short of the coast rather than weakened. The slip arrives with the season already forecast below normal, at 90% of the long-period average, under a building El Niño.
