A monsoon in May: Why have the rains arrived early in India?

Many Indian states, including Maharashtra and Kerala, have reported an early onset of monsoon this year. Incessant rainfall brought Mumbai to a standstill on Monday (May 26), with railway tracks and multiple low-lying areas being submerged in water.

Heavy downpours have lashed northern districts of Kerala, which witnessed the monsoon onset on Saturday, eight days ahead of its normal date of June 1. The monsoon rains also covered Lakshadweep, the south Arabian Sea, parts of the west-central and east-central Arabian Sea, and Karnataka.

But what’s behind the early onset of monsoon in India? Let’s understand.

Heavy rain hits Mumbai

The India Meteorological Department (IMD) declared the early arrival of monsoon in Maharashtra on Sunday (May 25), 10 days ahead of the usual onset on June 5. The last time monsoon arrived this early in Maharashtra was on May 20, 1990.

This is also the first time in 35 years that Mumbai reported the earliest onset of monsoon.
Mumbai witnessed heavy showers overnight that continued into the morning. Traffic movement, flights and local trains have been affected due to the downpour.

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Waterlogging was reported at the low-lying areas of King’s Circle, Mantralaya, Dadar TT East, Parel TT, Kalachowki, Chinchpokali and Dadar station, which led to traffic snarls on Monday, reported PTI.

Flight operations were impacted due to heavy rains in Mumbai on Monday morning. “Due to bad weather (heavy rain) in Mumbai (BOM), all departures/arrivals and their consequential flights may get affected. Passengers are requested to keep a check on their flight status via spicejet.com/," SpiceJet posted on X.

#WeatherUpdate: Due to bad weather (heavy rain) in Mumbai (BOM), all departures/arrivals and their consequential flights may get affected. Passengers are requested to keep a check on their flight status via https://t.co/2wynECYWr0.

— SpiceJet (@flyspicejet) May 26, 2025

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Air India also issued a travel advisory, urging flyers to check the status of their flights before heading to the Mumbai airport.

#TravelAdvisory

Rain and thunderstorms are impacting flight operations in Mumbai.

To ensure a smooth travel experience, we encourage our passengers to check their flight status before heading to the airport: https://t.co/6ajUZVdGTe

— Air India (@airindia) May 26, 2025

As per the IMD, the Colaba coastal observatory reported 135 mm of rainfall till 8.30 am, while the Santacruz observatory recorded 33 mm.

“What we are witnessing right now is monsoon rainfall. The tip of Colaba in south Mumbai recorded extremely heavy rainfall during the morning, mainly due to the intense rainfall in the Raigad district area. Moderate to heavy spell of rainfall will continue throughout the day,” Sushma Nair, scientist at IMD, Mumbai, told Indian Express on Monday.

The IMD has issued a ‘yellow’ alert in the island city till Wednesday. Heavy rainfall is expected in Mumbai today, with gusty winds blowing at 40 kmph.

Early onset in other parts of India

Monsoon rains reached Kerala on May 24, the earliest arrival in the southern state since May 23, 2009, the IMD said on Saturday.

Last year, Kerala reported the onset of monsoon on May 30. Trees were uprooted, houses and low-lying areas inundated, and acres of agricultural land destroyed as severe downpours battered Kerala on Sunday.

Amid intense rains, tribal families in the Puzhamkuni hamlet in Wayanad’s Sultan Bathery were evacuated to relief camps, reported PTI.

By Sunday, the southwest monsoon advanced to Karnataka, Goa, and areas in the west-central and northern Bay of Bengal. It also reached parts of Mizoram, Manipur, and Nagaland.

Why India’s rains are early this year

A combination of favourable atmospheric and oceanic conditions drives the early arrival of the southwest monsoon in India.

According to the IMD, several factors worked in favour of the monsoon rains, including the Madden-Julian Oscillation (MJO), the Mascarene High, and the monsoon trough.

MJO is an “eastward moving disturbance of clouds, rainfall, winds, and pressure that traverses the planet in the tropics”, according to the National Oceanic and Atmospheric Administration (NOAA). It affects the monsoon in India.

The Mascarene High is a high-pressure area occuring around the Mascarene Islands — in the south Indian Ocean — during monsoons, according to the IMD.

Monsoon trough is an elongated low-pressure area spanning from the heat low (a low-pressure area that develops over the Arabian Sea) to the north Bay of Bengal.

The neutral El Nino–Southern Oscillation (ENSO) conditions were reported around May 13, which supports a normal or stronger monsoon, as per a Times of India (TOI) report.

The reduced snow cover over the Himalayan region could be another factor contributing to the early monsoon arrival.

Benefits of early rains

The southwest monsoon brings roughly 70 per cent of the rain that India needs for agricultural activities and replenishing aquifers and reservoirs.

The advancement of monsoon could be beneficial for sectors such as agriculture, fisheries, and livestock.

“Surplus pre-monsoon rainfall and an early monsoon onset will help farmers, especially in the southern and central states, to sow summer crops earlier than usual”, Ashwini Bansod, vice president for commodities research at Phillip Capital India, a Mumbai-based brokerage, told Reuters. 

“Abundant soil moisture and early sowing could potentially boost crop yields,” Bansod added.

With inputs from agencies