Southwest Monsoon onset likely before May 27: What this means for Tamil Nadu

On Tuesday (May 20), the IMD predicted that the southwest monsoon, which typically begins in Kerala on June 1, will now arrive earlier than May 27. This would also spread into southern parts of Tamil Nadu, marking its earliest onset since 2010, The Indian Express reported. According to the IMD, Tamil Nadu could face heavy rainfall till May 24, with pre-monsoon rainfall patterns across Karnataka, Maharashtra, and interior Tamil Nadu confirming the trend.

A day earlier, Chief Minister MK Stalin chaired a high-level meeting in Chennai to assess the state’s preparedness. “If our preparations are proactive, beyond the usual level of preparedness, we could avoid the impact of disasters,” Stalin told officials. The state’s priority now shifts from battling heatwaves to managing surging rain and flood risk.

Why the southwest monsoon is arriving early

A rare convergence of climatic variables may explain why the southwest monsoon is arriving early. A key driver is the early formation of an east-west shear zone, a belt of atmospheric instability that usually appears in late May. This year, the zone formed by mid-May, triggering low-pressure systems in both the Arabian Sea and the Bay of Bengal—textbook signals of an advancing monsoon.

Additionally, cyclonic circulation over the southeast Arabian Sea at 5.8 km altitude is intensifying, drawing in moist monsoon winds toward the southern peninsula. In the absence of El Niño, which tends to suppress rainfall and spike temperatures, this year’s conditions are favourable for both early and active monsoon onset.

While meteorologically the summer in India ends only when the monsoon is firmly established, Tamil Nadu is already witnessing conditions more typical of early June than mid-May. No heat waves have been reported so far this year—an unusual occurrence for a state that typically records 2–3 heatwave episodes each summer. Chennai’s temperatures have stayed below 40°C, a rarity that underscores the changing climate dynamics. And the IMD’s seasonal outlook suggests continued rainfall, with southwest monsoon rains expected to bring 30–40% of Tamil Nadu’s annual total, especially crucial for western and southern districts such as Coimbatore, Erode, and Tirunelveli.

Decadal analysis shows that southwest monsoon patterns in Tamil Nadu are shifting. According to IMD data, the rainfall intensity is increasing in districts like Theni (+2.0 mm/year) and Tirunelveli (+2.4 mm/year), while some regions like Namakkal (-2.5 mm/year) are seeing a decline. The monsoon’s onset date has advanced by 5–7 days in recent years, and pre-monsoon activity in May is intensifying.

According to the Regional Meteorological Centre in Chennai, the sky will remain partly cloudy in Chennai over the next 48 hours, with maximum temperatures around 40–41°C—a mild rise compared to earlier in the month. Heavy rain is forecast in interior districts like Erode, Nilgiris, and Tirupattur in the coming days, along with thunderstorms in coastal regions.

While Tamil Nadu’s primary rainfall season remains the northeast monsoon (October–December), this year’s strong and early southwest monsoon is expected to bring much-needed irrigation to the western belts and boost early-season farming. It also serves as a test of the state’s monsoon preparedness systems.

State efforts at preparedness

CM Stalin’s review meeting on Monday focused largely on the state’s readiness for an earlier onset of monsoon. Advising all concerned departments to work in tandem, he said, “If our preparations are effective, beyond the usual preparedness, we could avoid the impact of disasters.”

He announced that water from the Mettur Dam will be released on June 12, the traditional date for the cultivation of the Kuruvai paddy crop, which depends on the onset of the southwest monsoon for a steady water supply.

Stalin also directed the state Agriculture department to fast-track the desilting of canals, ensure availability of seeds and fertilisers, and implement the Kuruvai Special Package. “We are hopeful of a good season,” he added.

The CM warned of possible flash floods and landslides, particularly in the Nilgiris and Western Ghats. He urged officials to ensure 24×7 emergency control rooms, clean and stocked relief centres, real-time SMS alerts for power disruptions, and road safety measures in accident-prone zones.