The India Meteorological Department (IMD) has confirmed that Mumbai witnessed the southwest monsoon’s earliest onset in 75 years, arriving today 16 days ahead of its usual 11 June schedule. This historic event, surpassing records set in 1956, 1962, and 1971 when the monsoon arrived on 29 May in each of the years. Last year, the monsoon reached Mumbai on 25 June.
The arrival of the monsoon brought unprecedented rainfall with South Mumbai received over 200 mm of rain between midnight and 11 AM on 26 May, contributing to a surplus of over 700% above normal May rainfall. The district of Colaba recorded 105.2 mm between 8:30 AM and 11:30 AM on 26 May.
As heavy rains lashed the state of Maharashtra, the IMD issued a ‘red alert’ for Mumbai, and neighbouring districts of Thane, Raigad, and Ratnagiri, warning of “extremely heavy rainfall and thunderstorms with lightning and gusty winds at isolated places”.
Heavy rains caused widespread waterlogging, disrupting flights, trains, and road traffic. Mumbai Metro Line 3 services were suspended between Acharya Atre Chowk and Worli due to flooding,
The early arrival follows the monsoon’s onset into the state of Kerala on India’s south west coast on 24 May 24, which was also the earliest since 2009.
The IMD have indicated favourable atmospheric conditions, including neutral El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) phases, have been instrumental in the early monsoon progression. In addition a cyclonic system over the Indian peninsula, moving towards the Arabian Sea, along with a well-marked low-pressure area over south Maharashtra has facilitated early rains.
In April a forecast of above-normal cumulative rainfall in the 2025 monsoon season had been made by the IMD, although meteorologists stress that the monsoon arriving early or late in Kerala or Mumbai does not predict total seasonal rainfall or the extent of the cover across other parts of the country. The monsoon’s progression to other regions can depend on a number of local and global factors.
The forecast is for continued heavy rainfall in Mumbai and Maharashtra until at least 28 May, with favorable conditions for the progress of the monsoon into central India and the northeast.
The southwest monsoon is vital for India’s agriculture, sustaining 42% of the population and contributing 18.2% to the national GDP. It also plays a critical role in replenishing reservoirs essential for drinking water and power generation nationwide. While the early rains promise agricultural benefits, they also bring challenges like urban flooding as seen in Mumbai.
