Monsoon Start Update in India 2025
The India Meteorological Department (IMD) declared the monsoon onset over Kerala on May 24, 2025, eight days ahead of its usual start on June 1. This event marks the beginning of the southwest monsoon season from June to September, contributing over 70% of India's annual rainfall.
Criteria for Monsoon Onset Declaration
- Rainfall: 60% of 14 specified southern meteorological stations must report at least 2.5 mm of rainfall for two consecutive days.
- Wind Field: Westerly winds should maintain a depth of up to 600 hPa with speeds between 27-37 km/hr at 925 hPa.
- Outgoing Longwave Radiation (OLR): Values should be below 200 Watts per square metre.
Factors Influencing Early Monsoon Onset
- Madden-Julian Oscillation (MJO): Eastward-moving disturbance enhancing rainfall.
- Mascarene High: High-pressure area influencing heavy rains on India’s west coast.
- Convection: Increased vertical heat and moisture transport causing rainfall.
- Somali Jet: Strong cross-equatorial wind band strengthening monsoon winds.
- Heat-low: Low-pressure area acting like a suction for moist air enhancing rainfall.
- Monsoon Trough: Low-pressure area influencing rainfall patterns.
Current Monsoon Progress
The southwest monsoon has covered the southwest and east-central Bay of Bengal, Maldives, Comorin regions, and parts of the Arabian Sea, Kerala, Lakshadweep, and Mahe. It has also reached Mizoram, southern and coastal Karnataka, and Tamil Nadu, progressing further into central and eastern regions.
The Northern Limit of Monsoon now passes through several locations, indicating significant progress into central and northern regions earlier than usual.
