The Regional Meteorological Centre in Chennai has hoisted a red alert across seven north coastal Tamil Nadu districts including Chennai, Chengalpattu, Tiruvallur, Kancheepuram, Villupuram, Cuddalore, and Mayiladuthurai, forecasting isolated pockets of extremely heavy rainfall exceeding 20 centimeters on Wednesday, October 22, 2025, as a well-marked low-pressure area over the southwest Bay of Bengal intensifies into a depression with an upper air cyclonic circulation stretching 7.6 kilometers above mean sea level, drawing massive moisture influx along the delta and coastal belts that could trigger flash floods in urban underpasses and rural riverine zones reminiscent of the 2015 deluge that submerged 60 percent of Chennai under waist-deep water for nearly a week.

By Thursday, October 23, the system is projected to track west-northwest toward the north Tamil Nadu-south Andhra Pradesh coastline, sustaining an orange alert for Chennai, Chengalpattu, Kancheepuram, Tiruvallur, and Ranipet with very heavy rain between 12 and 20 centimeters, accompanied by thunderstorms, lightning, and gusts up to 50 kilometers per hour, while Doppler radar imagery from Karaikal and Sriharikota reveals embedded convective cells capable of dumping 5-7 centimeters in under an hour, a scenario that has prompted the Greater Chennai Corporation to preposition 300 suction pumps and 150 earth-movers at 45 chronic flooding hotspots including the Mambalam canal, Velachery lake perimeter, and the Buckingham Canal outlets near Marina Beach.

In the 24 hours ending 8:30 a.m. Tuesday, October 21, rainfall blanketed the state with Thangachimadam in Ramanathapuram logging 17 centimeters, Pamban 15 centimeters, Mandapam 14 centimeters, and Varattupallam in Erode 13 centimeters, while Chennai suburbs like Medavakkam, Velankanni, and Okkiyam Thoraipakkam recorded 9-10 centimeters, cooling maximum temperatures by 2-5 degrees Celsius to 28 degrees Celsius and saturating soil to 90 percent capacity, conditions that meteorologist P Senthamarai Kannan warns will amplify runoff and overwhelm the city’s 3,200-kilometer stormwater drain network unless silt clearance targets of 40,000 cubic meters are met before Wednesday noon.

Also Read: IMD Issues Yellow Alert as Kerala Braces for Heavy Rain, Floods

District administrations have declared holidays for schools and colleges in Chengalpattu, Tiruvallur, Cuddalore, Villupuram, Kallakurichi, Thanjavur, Tiruvarur, Puducherry, and Karaikal, with Chennai closing only schools to protect over 5 lakh students, while Chief Minister M.K. Stalin has mobilized 150 NDRF teams, 500 relief camps, and 10,000 sandbags along the Kosasthalaiyar and Cooum rivers, and issued a total fishing ban in the southwest Bay of Bengal where wave heights will surge to 3.5 meters, safeguarding 2 lakh fisherfolk and the ₹8,000 crore marine export economy from potential vessel losses.

As Diwali approaches on October 31, the looming deluge threatens to wash out ₹500 crore in firecracker sales and disrupt manufacturing in Sriperumbudur’s auto corridor, yet the IMD’s ensemble models maintain a 70 percent probability of the depression deepening further, with satellite surveillance via INSAT-3D refining hourly forecasts; residents are urged to stock essentials, avoid low-lying zones, and monitor the TN flood dashboard, transforming a potential catastrophe into a showcase of coordinated resilience against the northeast monsoon’s opening salvo.

Also Read: Red Alert in Tamil Nadu Amid Dual Cyclonic Systems, Heavy Rains Forecast