Tamil Nadu: why Oct–Dec rain matters for half its year

For most of India, the main rains come from June to September. Tamil Nadu is different. According to IMD, the state gets about 48% of its yearly rainfall during the northeast monsoon, from October to December. That is why this season decides how much water the state has for the rest of the year.

The outlook (forecast, 1 October 2026). IMD's Northeast Monsoon Outlook says south peninsular India as a whole is most likely to get normal rain. Southern Tamil Nadu leans towards normal to above-normal rain, while most of the rest of the region leans below normal. Above-normal temperatures are likely too.

So far. From 1 to 17 October, Tamil Nadu, Puducherry and Karaikal got 75 mm against a normal 77.1 mm, close to normal. Most neighbouring subdivisions were well short.

The dams start low. Tamil Nadu Agriculture Department data for 17 October show:

• Mettur: 24% of capacity, against 97% on the same day last year.
• Bhavanisagar: 21%, against 84%.
• Vaigai: 20%, against 66%.
• Papanasam: 12%, against 41%.

(Percentages calculated from the department's storage and capacity figures.)

What it means. Even a normal season may not fully refill reservoirs that start this low. IMD asks authorities to plan irrigation carefully and promote water conservation.

What you can do. Save water at home, follow your district's advisories and keep an eye on IMD Chennai forecasts, including heavy-rain alerts.

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