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The India Meteorological Department (IMD) declared the onset of the southwest monsoon over Kerala on Saturday, eight days ahead of its normal schedule of June 1. This is the earliest since 2009, when monsoon arrived in Kerala on May 23.
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. Data available since 1975 showed that monsoon reached Kerala the earliest in 1990 (on May 19).
But, over the last week, Kerala has been experiencing a steady increase in rainfall intensity. The IMD said the southwest monsoon has made simultaneous advance into Kerala, Lakshadweep and Mahe, parts of Karnataka and Mizoram, and many parts of Tamil Nadu.
The IMD has forecast extremely heavy rainfall (over 205 mm in 24 hours) in Kerala, Mahe and coastal Karnataka until Monday. The northern limit of monsoon, which is an imaginary line marking the progress of the southwest monsoon, now passes through Karwar and Shimoga in Karnataka, Dharamapuri and Chennai in Tamil Nadu and Siaha (Mizoram).
Over the next two to three days, favorable conditions will aid the further advance of monsoon into parts of Maharashtra and Andhra Pradesh, more parts of Karnataka and sub-Himalayan West Bengal and Sikkim, remaining parts of Tamil Nadu, Goa, and more parts of central Arabian Sea.
It is likely to advance over remaining parts of south peninsular and northeast India, and some more parts of east and central India during May 29-June 4.
early arrival of monsoon has no bearing on the amount of rainfall that can be expected during the four-month season. Weather has not been playing to the script this year — May hasn’t been as hot as expected. Parts of central and western India have seen unusual rainfall over the last week.
Speaking to The Indian Express, IMD Director General Mrutyunjay Mohapatra said, “Conditions will be favourbale for further advance of the monsoon to more regions along the southern peninsular, more parts of Arbaian sea and Bay of Bengal. It will not be a surprise if the monsoon reaches some parts of central and east India in the coming few days.”
The IMD considers three main factors ahead of declaring the onset over Kerala, which marks the beginning of the four-month-long rainy season over the country. These are: rainfall measuring 2.5mm or more reported over 14 meteorological stations for at least two consecutive days; deep penetration of westerly winds; outgoing longwave radiation value falling below 200 Wm-2.
The IMD in April forecast above-normal rainfall this year, expected to be 105 per cent of the Long Period Average (LPA) of 880 mm. During the next four months, the major ocean factors that influence the southwest monsoon — the El Nino Southern Oscillation and the Indian Ocean Dipole — will remain in ‘neutral’ phase and have positive influence on the rainfall over India, it had said earlier.
Southwest monsoon onset over Kerala in the last few years:
| Year | Realised date | Year | Realised date |
| 2025 | May 24 | 2016 | June 8 |
| 2024 | May 30 | 2015 | June 5 |
| 2023 | June 8 | 2014 | June 6 |
| 2022 | May 29 | 2013 | June 1 |
| 2021 | June 3 | 2012 | June 4 |
| 2020 | June 1 | 2011 | June 2 |
| 2019 | June 8 | 2010 | May 31 |
| 2018 | May 29 | 2009 | May 23 |
| 2017 | May 30 |
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