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The Southwest Monsoon (SWM) has made rapid initial progress and reached as far north as Mumbai in Maharashtra, southern Telangana, Andhra Pradesh and almost the entirety of Northeast India after its onset on May 24, 2025. But the spectre of stalling and less rains in the coming weeks remain with the formation of a low-pressure area in the Bay of Bengal.
The onset over Kerala was eight days earlier than the normal date of June 1. For Mizoram, where the monsoon arrived on the same day as Kerala, the onset was 12 days earlier than normal. The onset in other areas has also been more than two weeks earlier than normal. For Mumbai city this is the earliest onset in the last 25 years, according to the India Meteorological Department (IMD).
The monsoon “has further advanced into some more parts of central Arabian Sea, some more parts of Maharashtra including Mumbai, Karnataka including Bengaluru, remaining parts of Tamil Nadu, some parts of Telangana and Andhra Pradesh, some more parts of west-central & North Bay of Bengal, Remaining parts of Mizoram, entire Tripura, Manipur, Nagaland, Arunachal Pradesh, some parts of Assam and Meghalaya, today the 26th May”, said the IMD in a press release.
As the monsoon winds move forward, they have been aided by a low-pressure area that formed in the Arabian Sea and persisted over Marathwada and adjoining areas on May 26. An upper air trough also exists from the low-pressure area to northwest Bay of Bengal, according to the IMD. The low-pressure system and the upper air trough could have pulled the Arabian Sea branch of the monsoon northward into Maharastra, Telangana and Andhra Pradesh.
There are active weather systems in north and northwest India as well causing thunderstorms with heavy to extremely heavy rainfall. The IMD highlighted the persistence of a western disturbance as an upper air circulation over Haryana and a trough in the westerlies. Another upper air circulation exists over southwest Rajasthan.
Delhi and Haryana received heavy rainfall due to the above systems on May 24-25. Delhi received 44.4 mm absolute rainfall on May 24-25 which was 8,782 per cent more than the normal for the day. The highest rainfall of 77.1 mm occurred over central Delhi, a 6,321 per cent excess.
Haryana received 29.5 mm absolute rainfall on May 24-25 which was 9,737 per cent more than the normal for the day. Panipat received the highest rainfall of 55.6 mm, a humongous 55,483 per cent excess.
In the Northeast, an upper air cyclonic circulation was present over northeast Assam. This circulation, along with the incoming monsoon winds, could precipitate heavy to extremely heavy rainfall in the region.
“Fairly widespread to widespread light/moderate rainfall accompanied with thunderstorm, lightning over Northeast India during next 7 days,” the IMD said on May 26 in a press release.
“Isolated heavy rainfall likely over Arunachal Pradesh, Assam & Meghalaya, Nagaland, Manipur, Mizoram & Tripura during 26th May-01st June with isolated very heavy rainfall likely over Nagaland, Manipur, Mizoram & Tripura during 28th May-01st June and Assam & Meghalaya during 29th May-01st June,” the weather agency added.
The rains would be welcome in the region as it was going through a dry patch during the pre-monsoon season, unlike the rest of the country. Many states were under nominal to severe deficits during the pre-monsoon. Mizoram received 55 per cent less rainfall than normal, the highest deficit in the region, between March 1 and May 25 while Tripura had a deficit rainfall of 42 per cent. Arunachal Pradesh and Manipur received 40 per cent less rainfall than normal in the same period. Nagaland had a deficit of 25 per cent.
The country as a whole has received 22 per cent excess rainfall during the pre-monsoon season between March 1 and May 25, 2025.
IMD has also indicated the formation of a low-pressure area in the west-central and adjoining north Bay of Bengal on May 27. The formation of low-pressure areas that have intensified into cyclones has led to the stalling of the monsoon winds in previous years such as in 2024 and 2021. Whether such stalling occurs in the current season after a swift progress, leading to heat waves and short-term drought-like conditions, remains to be seen.