Tamil Nadu Weather Update – October 21, 2025
Introduction
Tamil Nadu has entered a highly active weather phase as the Northeast Monsoon continues to strengthen across the region. As of October 21, 2025, the India Meteorological Department (IMD) has issued multiple red and orange alerts for districts along the coast and interior regions due to heavy to extremely heavy rainfall. A low-pressure system over the southwest Bay of Bengal has intensified, bringing widespread rain, thunderstorms, and gusty winds across the state.
Residents in Chennai, Cuddalore, Kancheepuram, Puducherry, and nearby areas have already reported intense rainfall, waterlogging, and intermittent power disruptions. The situation is being closely monitored by local authorities, with the IMD advising caution and preparedness for the next 48 hours.
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Meteorological Overview
Satellite imagery confirms that a well-marked low-pressure area has formed over the southwest Bay of Bengal, just off the Tamil Nadu coast. Upper-air circulation associated with this system has enhanced convective activity and moisture inflow from the sea. As a result, thunderstorms and heavy showers are occurring intermittently throughout the state, especially during late evenings and early mornings.
The system’s slow movement and warm sea surface temperatures around 29°C are prolonging rainfall intensity. Additionally, due to the interaction between easterlies and westerlies, moisture bands are spreading inland, triggering rain even in central districts such as Madurai, Dindigul, and Tiruchirappalli.
Current Weather Conditions by Region
Chennai and Surrounding Districts
Chennai, the state capital, has been receiving continuous moderate to heavy rainfall since early morning. The city’s core areas — including T. Nagar, Velachery, Adyar, and Anna Nagar — recorded more than 120mm of rain within a single day. Surface winds are blowing at speeds of 30–45 km/h, occasionally gusting up to 55 km/h.
The air remains humid with levels around 94%, and the temperature has remained largely mild, fluctuating between 26°C and 28°C. The Greater Chennai Corporation has advised residents to avoid low-lying underpasses and keep emergency supplies ready in case of flooding.
Coastal Districts (Cuddalore, Nagapattinam, Karaikal)
These districts are currently facing very heavy rainfall, with some locations recording over 200mm in the past 24 hours. Strong onshore winds continue to drive moisture-laden clouds inland, resulting in intense rainfall episodes. Fishermen have been strictly warned not to venture into the sea, as wave heights are expected to reach up to 3.5 meters in nearshore areas.
The IMD predicts continued rainfall and the possibility of flash flooding in river-adjacent villages. Relief teams have been placed on standby to respond to emergencies.
Delta and Interior Districts (Thanjavur, Tiruvarur, Pudukkottai)
The Cauvery Delta region is seeing widespread rainfall that benefits agricultural zones but also poses challenges for low-lying paddy fields. The irrigation department has begun controlled water releases from reservoirs to manage inflows. There have been reports of localized flooding in narrow road networks, but overall conditions remain manageable.
Farmers have welcomed the consistent showers but are cautious about potential waterlogging over the coming days.
Southern and Western Tamil Nadu (Madurai, Dindigul, Coimbatore)
Western and southern districts have experienced light to moderate showers in the past 12 hours, with scattered thunderstorms developing by late evening. The temperature has dropped slightly, with Madurai recording around 25°C during the night — about 3°C below seasonal norms. Coimbatore remains partly cloudy, with isolated rainfall expected as the system drifts westward.
Forecast and Rainfall Outlook
IMD forecasts suggest that the low-pressure area could intensify into a depression over the next 24 hours, bringing more rainfall to northern and coastal districts. The probability of extremely heavy rain (over 20 cm in 24 hours) is high in Chennai, Villupuram, Cuddalore, and Mayiladuthurai.
Over the next three days, most of Tamil Nadu will experience moderate rainfall, with coastal regions bearing the heaviest intensity. Interior areas such as Salem, Karur, and Namakkal are expected to see intermittent light rain accompanied by thunderstorms.
Long-range satellite models also show a possible second system forming over the Bay of Bengal by the weekend, which could sustain active monsoon conditions until the end of the month.
Air Quality and Temperature Trends
Despite the heavy rain, air pollution remains a concern in urban centers. Chennai’s air quality index (AQI) has reached unhealthy levels (120–150 range) due to high particulate matter trapped by humidity. Residents with respiratory conditions are advised to limit exposure to outdoor air during peak evening hours.
Temperature across Tamil Nadu is currently below normal:
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Chennai: 27°C (2°C below average)
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Madurai: 25°C (3°C below average)
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Tiruchirappalli: 26°C
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Coimbatore: 24°C
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Nagapattinam: 28°C
Humidity remains above 90% in most districts, supporting continuous cloud formation.
Safety Measures and Public Advisory
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Avoid traveling during heavy rainfall; postpone nonessential trips to coastal routes.
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Do not attempt to cross flooded roads or bridge sections with high current flow.
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Keep valuable electronics and documents elevated in low-lying homes.
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Monitor IMD, NDMA, and local authority updates for real-time alerts.
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Fishermen and small boat operators should remain docked until wind strength subsides below 25 km/h.
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Schools in Chennai, Cuddalore, Villupuram, and surrounding areas are likely to remain closed tomorrow for safety reasons.
Climate Context: The Northeast Monsoon Effect
The Northeast Monsoon is Tamil Nadu’s primary rainy season, contributing 48% of the state’s annual rainfall. It typically begins in mid-October and lasts through December. This year’s early onset has aligned with a neutral ENSO phase, providing favorable atmospheric conditions for sustained rain events.
The ongoing low-pressure activity marks the first strong system of the season, setting the stage for a wetter-than-average October. Meteorologists are closely observing air circulation patterns, especially within the Bay of Bengal, as these often shape cyclone developments during the monsoon window.
Conclusion
Tamil Nadu’s weather on October 21, 2025, is dominated by heavy to extremely heavy rainfall under an evolving low-pressure system. With widespread showers impacting both coastal and inland areas, residents must stay alert and adhere to safety advisories. The IMD and state authorities continue to monitor the situation closely, ensuring timely information and relief operations.
As rainfall persists into the week, coastal and delta districts are encouraged to prepare for extended wet conditions. Meanwhile, drier regions in the west may see brief relief before another potential system forms later this month.
Stay tuned to trusted weather portals such as IMD Chennai, KWS Chennai, and Kea Weather Blog for timely updates on rainfall intensity, flood alerts, and wind forecasts.
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