The Southwest Monsoon made an early entry into India this year, arriving in Kerala on May 24, a full eight days ahead of its normal schedule of June 1. The last time the monsoon came this early was in 2009, when it arrived on May 23.
The India Meteorological Department (IMD) officially declared the onset of the monsoon over Kerala on Saturday, marking the beginning of the country’s critical four-month monsoon season (June–September) — a weather system that delivers over 70% of India’s annual rainfall, essential for agriculture, water supply, and economic stability.
🌀 Why Did the Monsoon Arrive Early in 2025?
Experts from IMD and climate scientists say a convergence of multiple atmospheric and oceanic factors aligned this year to accelerate the onset of monsoon over the southern coast.
🔑 Key Factors Behind the Early Onset:
1. Madden-Julian Oscillation (MJO)
The MJO, a pulse of cloud and rainfall activity that travels around the globe, was in a favorable phase over the Indian Ocean in mid-May. This triggered enhanced convection and cloud development, supporting early monsoon conditions.
2. Weakened El Niño Conditions
The El Niño phenomenon, which typically weakens monsoon systems, is now transitioning toward neutral or La Niña-like conditions. This transition reduced atmospheric suppression over the Indian subcontinent, paving the way for an earlier onset.
3. Warm Sea Surface Temperatures (SSTs)
The Arabian Sea and Bay of Bengal witnessed above-normal SSTs, which fueled rapid low-pressure development and strong moisture inflow — key indicators that meet IMD's criteria for declaring the monsoon onset.
4. Formation of Cyclonic Circulations
A series of pre-monsoon weather systems, including cyclonic circulations near the Lakshadweep and southern Arabian Sea, helped accelerate monsoon winds and rainfall bands toward Kerala and the southern peninsula.
5. Strong Westerly Winds at Surface and Upper Levels
Consistent moist westerly winds, both at the lower and mid-tropospheric levels, contributed to deep cloud formation and sustained rainfall over Kerala and coastal Karnataka.
🌧️ How Does IMD Declare Monsoon Onset?
IMD declares monsoon onset based on a combination of meteorological parameters:
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60% of 14 selected meteorological stations in Kerala must report at least 2.5 mm rainfall for two consecutive days.
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A steady increase in moisture levels from the Arabian Sea.
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A significant shift in wind patterns (from easterlies to southwesterlies).
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Outgoing Longwave Radiation (OLR) values below 200 W/m², indicating dense cloud cover.
All of these criteria were met by May 24, 2025, leading to the official declaration.
📈 Why the Monsoon Onset Date Matters
The timing of the monsoon has direct implications for agriculture, water resources, and economic planning in India:
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Farmers plan sowing activities based on the arrival of rains.
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Reservoir management and irrigation planning depend on rainfall predictions.
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Food inflation and GDP projections are influenced by monsoon reliability.
An early onset can benefit early sowing but also raises concerns if followed by dry spells or uneven rainfall distribution.
📍 What Happens Next?
IMD will now monitor the progress of the monsoon toward central and northern India in the coming weeks. The early onset raises hopes of a timely or early advance across the rest of the country, though intra-seasonal variability could still occur.
🌿 Climate Experts’ Take
“The early onset this year is not unprecedented but definitely a significant anomaly,”
— Dr. Roxy Mathew Koll, climate scientist at the Indian Institute of Tropical Meteorology (IITM), Pune.“We must be cautious not to confuse early onset with good rainfall throughout. Continuous monitoring is critical,”
— Sunitha Devi, scientist at IMD Monsoon Desk.