The southwest monsoon made landfall in Kerala on May 25, eight days ahead of its normal onset date of June 1, the India Meteorological Department (IMD) confirmed on Saturday. This marks the earliest arrival of monsoon rains on the Indian mainland since 2009, when it began on May 23.
The early onset signals the start of India’s critical four-month monsoon season, which accounts for over 70% of the country’s annual rainfall. Its timely arrival is not just a meteorological milestone but a vital economic indicator, particularly for the agriculture sector that remains heavily dependent on monsoon-fed water.
The IMD had predicted an early onset around May 27, allowing a four-day margin on either side. “The monsoon onset took place today, 24th May, which is much ahead of its schedule. Our forecast has come true,” IMD scientist Neetha K Gopal told ANI, a TOI report quoted.
Where has the monsoon reached?
According to the India Meteorological Department (IMD), it has already covered Kerala, the Lakshadweep area and extended into the south Arabian Sea, as well as parts of the west-central and east-central Arabian Sea. On the Indian mainland, it has reached southern parts of Karnataka and Maharashtra.
As per a report by TOI, additionally, the monsoon has spread across the Maldives, Comorin region, many parts of Tamil Nadu and the southwest and east-central Bay of Bengal. It has also touched parts of Mizoram and the northern Bay of Bengal.
IMD officials quoted by TOI stated that conditions remain favourable for its further advance into the central Arabian Sea, Goa, more parts of Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu and deeper into the northeastern states, including Sub-Himalayan West Bengal and Sikkim, over the next few days.
According to the Indian Express, this marks the earliest onset over several states in recent memory. For instance, in Karnataka, the monsoon typically begins around June 5; this year, it arrived as early as May 24.
The southwest monsoon’s early arrival in India this year has broken multiple records and triggered widespread alerts across states.
In Maharashtra, the monsoon reached on May 25 - the earliest in 35 years. Mumbai recorded its wettest May in over a century with 295 mm of rainfall, surpassing the previous record of 279.4 mm set in 1918. The downpour caused waterlogging in parts of the city, including newly inaugurated underground Metro-3 stations and suburban train tracks, disrupting services. Civic officials and the IMD faced criticism over preparedness, as per a TOI report.
In Telangana, the monsoon arrived nearly 10 days ahead of schedule — the earliest onset in a decade. The IMD declared its arrival on May 27, with a yellow alert issued across the state warning of heavy rain, thunderstorms, and squalls through the end of the month, Money Control reported.
Karnataka too saw an early onset, with intense rain lashing Mysuru, Kodagu, and coastal districts. A red alert was issued on May 27, with forecasts indicating a wet spell for Bengaluru. Similar early arrivals were last seen in 2001 and 2009, as per Hindustan Times.
What caused the early onset?
A mix of large-scale atmospheric and oceanic phenomena, along with regional weather systems, contributed to the early arrival of monsoon rains.
According to the IMD, a low-pressure system formed over the Arabian Sea, along with a trough extending across Vidarbha, helped channel moisture into the subcontinent, enhancing convection and hastening the monsoon’s advance.
Several other favourable elements aligned this year:
- The Madden-Julian Oscillation (MJO): A major atmospheric disturbance from the Indian Ocean that enhances rainfall when in its active phase.
- The Somali Jet: A cross-equatorial wind system that strengthens monsoon currents as it moves from the African coast to India.
- Mascarene High: A high-pressure system near the Mascarene Islands that, when intensified, drives moist winds toward the Indian west coast.
- Convection: An uptick in vertical transport of heat and moisture in the atmosphere further boosted rain activity.
Heat-low over Pakistan and adjoining areas: This created a suction effect, pulling moist air inland and reinforcing monsoon conditions.
Additionally, satellite data showed low values of Outgoing Longwave Radiation (OLR), another key indicator used by the IMD to declare monsoon onset. Values below 200 watts per square metre signal increased cloud formation and rainfall potential, aligning with favourable conditions, the Indian Express report added.
Also noted were neutral El Niño–Southern Oscillation (ENSO) conditions — a state which typically supports a normal or robust monsoon season. Reduced Himalayan snow cover, which often correlates with stronger monsoonal flow, may have also played a role.
How is the onset declared?
The IMD uses a combination of parameters to officially declare monsoon onset over Kerala:
- Rainfall: At least 60% of 14 designated stations in southern India must receive 2.5 mm or more of rain for two consecutive days.
- Winds: Westerly winds must prevail at a depth of 600 hPa with speeds of 15–20 knots (27–37 km/h).
- OLR values: Satellite-observed radiation levels should remain under 200 watts per square metre.
Once all the key meteorological criteria are met for two consecutive days, the IMD officially declares the onset of the monsoon over Kerala. In 2025, this declaration came alongside a widespread and simultaneous onset — not just over Kerala, but also across the entire Lakshadweep region, Mahe (Puducherry) and large sections of both the Arabian Sea and Bay of Bengal. Monsoon winds had also reached parts of southern Karnataka and Mizoram in northeast India, marking a notably broad and early advance of the season’s rains.
These conditions were fulfilled by May 24, prompting the IMD’s declaration. As per the Indian Express, the IMD typically begins evaluating monsoon conditions from May 10 onwards each year.
Impact and what lies ahead
The early and vigorous onset is expected to benefit crucial sectors like agriculture, fisheries and livestock, especially in states where rainfall is a primary water source. It also reflects the growing accuracy of India’s weather forecasting systems, bolstered by initiatives like the Monsoon Mission and high-performance computing models, TOI reported.
However, the early rains have also led to severe weather alerts. Red warnings were issued for Kerala’s Kasaragod and Kannur districts on Saturday, while 11 other districts, including Thiruvananthapuram and Ernakulam, were placed under orange alerts.
The IMD reported heavy to very heavy rainfall across Kerala, Mahe and coastal Maharashtra, with isolated heavy showers in parts of Karnataka, Odisha, Bihar, Madhya Maharashtra, Goa, Uttarakhand, Vidarbha, Saurashtra, Kutch and Tamil Nadu (including Puducherry and Karaikal).
In the Nilgiris district of Tamil Nadu, authorities have reportedly halted all boating activities and advised residents in Ooty and surrounding areas to remain indoors unless necessary.
What’s next?
Conditions remain favourable for the monsoon to push further into the central Arabian Sea, more areas of Maharashtra and Andhra Pradesh, deeper sections of Karnataka and Tamil Nadu and northeastern states including sub-Himalayan West Bengal and Sikkim over the coming days.
While the southwest monsoon has started strong, IMD officials say it’s too early to draw conclusions about the northeast monsoon or overall seasonal rainfall. “Let us monitor the progress and then we will issue the long-range forecast,” TOI quoted B Amudha, head of the Regional Meteorological Centre as telling ANI.
Discover the latest Business News, Sensex, and Nifty updates. Obtain Personal Finance insights, tax queries, and expert opinions on Moneycontrol or download the Moneycontrol App to stay updated!
