New Delhi: The India Meteorological Department (IMD) announced the onset of the southwest monsoon over Kerala on May 24, 2025, a remarkable eight days ahead of its typical June 1 schedule. This marks the earliest monsoon arrival in 16 years, since May 23, 2009, and three days earlier than the IMD’s forecast of May 27. The early onset, driven by a unique combination of atmospheric and oceanic phenomena, signals a promising start to India’s critical four-month monsoon season, which delivers over 70% of the country’s annual rainfall.
Southwest Monsoon: The Lifeblood of India’s Economy
The southwest monsoon, occurring from June to September, is a seasonal wind system that brings nearly 70% of India’s rainfall, vital for the nation’s $4 trillion economy. It supports agriculture, replenishes aquifers and reservoirs, and sustains livelihoods, particularly in the 50% of India’s farmland that lacks irrigation and depends entirely on monsoon rains. Crops such as rice, corn, cotton, soybeans, and sugarcane rely on these rains, making the monsoon’s timely arrival a critical economic indicator.
This year, the monsoon has not only reached Kerala but also extended to parts of Tamil Nadu, Karnataka, Mizoram, and the Lakshadweep region, as well as the south Arabian Sea, west-central and east-central Arabian Sea, Maldives, Comorin region, and the southwest and east-central Bay of Bengal. The IMD predicts favorable conditions for the monsoon to advance further into Goa, parts of Maharashtra, Andhra Pradesh, northeastern states, sub-Himalayan West Bengal, and Sikkim within the next two to three days.
Record-Breaking Early Onset: A Milestone Since 2009
The monsoon’s arrival on May 24, 2025, is a significant milestone, marking the earliest onset since 2009. In contrast, the 2024 monsoon arrived on May 30, two days ahead of schedule. The IMD’s accurate prediction, with a four-day margin around May 27, underscores the advancements in India’s weather forecasting systems, bolstered by initiatives like the Monsoon Mission and high-performance computing models.
The early onset has broken multiple records across states. In Maharashtra, the monsoon arrived on May 25, the earliest in 35 years, with Mumbai recording its wettest May in over a century at 295 mm of rainfall, surpassing the 1918 record of 279.4 mm. In Telangana, the monsoon arrived nearly 10 days early on May 27, the earliest in a decade. Karnataka saw an early onset on May 24, compared to its typical June 5 start, with heavy rains in Mysuru, Kodagu, and coastal districts.
IMD’s Criteria for Declaring Monsoon Onset
The IMD follows stringent criteria to declare the monsoon’s onset over Kerala, ensuring accuracy in its announcements. These criteria include:
- Rainfall Trigger: At least 60% of 14 designated meteorological stations, including Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu, and Mangalore, must record rainfall of 2.5 mm or more for two consecutive days.
- Wind Field Criteria: Westerly winds, blowing from west to east in the 30 to 60-degree latitudes, must extend up to 600 hPa (approximately 3-4 kilometers above sea level) with zonal wind speeds of 15–20 knots (27–37 km/h) at 925 hPa.
- Outgoing Longwave Radiation (OLR): Satellite-derived OLR, a measure of energy emitted to space by Earth’s surface, oceans, and atmosphere, must be below 200 watts per square meter, indicating active convection and cloud cover.
These conditions were met by May 24, prompting the IMD’s declaration. The simultaneous onset across Kerala, Lakshadweep, Mahe (Puducherry), and parts of the Arabian Sea and Bay of Bengal highlights the broad and vigorous advance of the 2025 monsoon.
Factors Driving the Early Monsoon Onset
Several atmospheric and oceanic phenomena aligned to facilitate the early arrival of the 2025 monsoon:
- Madden-Julian Oscillation (MJO): This atmosphere-ocean coupled phenomenon, observed from May 13 over the south Andaman Sea, enhanced cloud and wind patterns, boosting convection and rainfall over the Indian Ocean.
- Mascarene High: A high-pressure system near the Mascarene Islands in the southern Indian Ocean intensified monsoon flow, directing moist winds toward India’s west coast.
- Somali Jet: A low-level, cross-equatorial wind band originating near Mauritius and north Madagascar strengthened monsoon currents over the Arabian Sea.
- Convection Surge: Increased vertical transport of heat and moisture in the atmosphere led to enhanced cloud build-up and early rainfall.
- Heat Low: An intense low-pressure zone over Pakistan and northwest India acted as a suction device, pulling moist air along the monsoon trough.
- Monsoon Trough: An elongated low-pressure area extending from the heat low to the North Bay of Bengal shifted southward, activating rainfall across central and northeast India.
- Neutral El Niño–Southern Oscillation (ENSO): Neutral ENSO conditions, combined with reduced Himalayan snow cover, supported a robust monsoon flow.
- Pre-Cyclonic Storm: A low-pressure system over the Konkan-Goa coast, expected to make landfall on May 24, further enhanced convection and moisture inflow.
Low OLR values, as reported by the Indian Express, also confirmed increased cloud formation and rainfall potential, aligning with the IMD’s criteria.
Impacts of the Early Monsoon
The early monsoon onset brings both opportunities and challenges across various sectors:
Agriculture and Water Security
- Boost to Farming: The early rains enable farmers to sow Kharif crops like paddy and pulses earlier, improving adherence to the crop calendar. Ashwini Bansod, vice president for commodities research at Phillip Capital India, noted that abundant soil moisture could boost crop yields, particularly in southern and central states.
- Reservoir Recharge: Early rainfall will replenish water levels in drought-prone states like Tamil Nadu and Karnataka, supporting water security.
- Economic Implications: With nearly half of India’s farmland relying on monsoon rains, the early onset promises a bumper harvest, potentially stabilizing food prices and supporting rural economies.
Challenges and Risks
- Urban Flooding: The early rains have caused disruptions, particularly in urban areas. Mumbai’s record-breaking May rainfall led to waterlogging in newly inaugurated Metro-3 stations and suburban train tracks, highlighting civic unpreparedness. Bengaluru faces similar risks, with forecasts indicating a wet spell.
- Severe Weather Alerts: The IMD issued red alerts for Kerala’s Kasaragod and Kannur districts and orange alerts for 11 others, including Thiruvananthapuram and Ernakulam. Heavy rainfall warnings extend to coastal Maharashtra, Karnataka, Odisha, Bihar, Madhya Maharashtra, Goa, Uttarakhand, Vidarbha, Saurashtra, Kutch, and Tamil Nadu.
- Uncertain Monsoon Progression: While the early onset is promising, the IMD cautions that it does not guarantee a longer or stronger monsoon season. In 2009, despite an early start, India faced a 23% rainfall shortfall, underscoring the need for sustained monsoon currents.
Regional Impacts and Weather Alerts
The monsoon’s early arrival has triggered widespread alerts and disruptions:
- Kerala: Heavy to very heavy rainfall prompted red alerts in Kasaragod and Kannur, with orange alerts in 11 other districts. The state saw vigorous monsoon spells, with heavy rains lashing Thiruvananthapuram’s Shangumugham beach on May 24.
- Maharashtra: Mumbai’s record 295 mm rainfall caused waterlogging and disrupted transport services, drawing criticism for civic preparedness.
- Telangana: A yellow alert was issued through May’s end, warning of heavy rain, thunderstorms, and squalls.
- Karnataka: Intense rains in Mysuru, Kodagu, and coastal districts prompted a red alert for Bengaluru on May 27.
- Tamil Nadu: Authorities in the Nilgiris district halted boating activities and advised residents to stay indoors due to heavy rainfall.
What Lies Ahead for Monsoon 2025?
The IMD forecasts favorable conditions for the monsoon to advance into the central Arabian Sea, more areas of Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, and northeastern states over the next few days. However, officials caution that it’s too early to predict the northeast monsoon or overall seasonal rainfall. B Amudha, head of the Regional Meteorological Centre, told ANI, “Let us monitor the progress and then we will issue the long-range forecast.”
The IMD’s April forecast predicted above-average monsoon rainfall for 2025, ranging between 96% and 104% of the 50-year average of 87 cm (35 inches). If realized, this would mark the second consecutive year of above-normal rainfall, following an 8% surplus in 2024.
Conclusion: A Promising Yet Challenging Season
The early onset of the 2025 southwest monsoon, driven by favorable atmospheric and oceanic conditions like the MJO, Somali Jet, and Mascarene High, offers hope for India’s agriculture, water security, and economy. However, it also underscores the need for preparedness against urban flooding, infrastructure disruptions, and potential rainfall variability. As the monsoon progresses, India’s advanced forecasting systems will play a crucial role in guiding farmers, policymakers, and citizens through this vital season.
Frequently Asked Questions
1. When did the southwest monsoon arrive in Kerala in 2025, and why is it significant?
The southwest monsoon arrived in Kerala on May 24, 2025, eight days earlier than its usual June 1 schedule, marking the earliest onset since May 23, 2009. This early arrival is significant as it delivers over 70% of India’s annual rainfall, crucial for agriculture, water security, and the $4 trillion economy. It allows early sowing of Kharif crops like rice and pulses, potentially boosting yields, and supports reservoir replenishment in drought-prone areas.
2. What factors contributed to the early onset of the 2025 monsoon?
The early onset was driven by several atmospheric and oceanic phenomena:
Neutral ENSO and Reduced Snow Cover: These conditions supported a robust monsoon flow.
A pre-cyclonic storm over the Konkan-Goa coast on May 24 further enhanced moisture inflow.
Madden-Julian Oscillation (MJO): Enhanced cloud and wind patterns from May 13 over the Andaman Sea boosted rainfall.
Mascarene High: A strong high-pressure system near the Mascarene Islands directed moist winds toward India.
Somali Jet: Strengthened cross-equatorial winds accelerated monsoon currents over the Arabian Sea.
Convection Surge: Increased vertical transport of heat and moisture spurred cloud formation.
Heat Low: A low-pressure zone over Pakistan and northwest India pulled moist air inland.
Monsoon Trough: Its southward shift activated rainfall across central and northeast India.
3. How does the India Meteorological Department (IMD) declare the monsoon onset?
The IMD uses three criteria to declare the monsoon’s onset over Kerala:
Outgoing Longwave Radiation (OLR): Satellite-derived OLR must be below 200 watts per square meter, indicating active convection and cloud cover.
These conditions were met by May 24, 2025, prompting the IMD’s declaration.
Rainfall: At least 60% of 14 designated stations (e.g., Minicoy, Thiruvananthapuram, Kochi) must record ≥2.5 mm of rain for two consecutive days.
Wind Field: Westerly winds must extend up to 600 hPa with speeds of 15–20 knots at 925 hPa.
4. What are the impacts of the early monsoon onset in 2025?
Benefits:
- Agriculture: Early sowing of crops like paddy and pulses could improve yields, especially in southern and central states.
- Water Security: Early rains will replenish reservoirs in drought-prone areas like Tamil Nadu and Karnataka.
Economic Stability: Supports rural economies by ensuring water for nearly 50% of India’s unirrigated farmland.
Challenges:
- Urban Flooding: Heavy rains caused waterlogging in Mumbai and pose risks in Bengaluru.
- Severe Weather: Red and orange alerts were issued for Kerala, Maharashtra, Karnataka, and other states due to heavy rainfall and thunderstorms.
Uncertain Progression: An early onset does not guarantee a strong or prolonged monsoon, as seen in 2009 with a 23% rainfall shortfall.
5. Which regions have been affected by the 2025 monsoon so far, and what’s next?
By May 28, 2025, the monsoon has covered Kerala, Lakshadweep, Mahe, parts of Tamil Nadu, Karnataka, Mizoram, the south Arabian Sea, west-central and east-central Arabian Sea, Maldives, Comorin region, and parts of the Bay of Bengal. Maharashtra saw its earliest onset in 35 years on May 25, and Telangana’s monsoon arrived 10 days early on May 27. The IMD forecasts further advance into Goa, more parts of Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, northeastern states, sub-Himalayan West Bengal, and Sikkim in the next 2–3 days. However, the overall seasonal rainfall and northeast monsoon outlook remain uncertain, with the IMD monitoring progress for long-range forecasts.
