Earliest Onset Of Monsoon For Tamil Nadu: Heavy Rains Likely

Key Takeaways:

• The northeast monsoon has commenced over Tamil Nadu on October 15, 2026, matching 2024 as the earliest onset since 2010.
• Tamil Nadu receives approximately 48% of its annual rainfall during the three-month northeast monsoon season.
• Nagapattinam and Karaikal recorded 91 mm and 76 mm of rainfall, respectively, on Wednesday, while Karaikal received another 56 mm on Thursday afternoon.
• Coastal and interior Tamil Nadu are likely to receive good rainfall over the next four days, followed by light to moderate showers for another 3–4 days.
• Forecast Validity: October 15–22, 2026

The preconditions for the onset of the northeast monsoon are fairly widespread rainfall along coastal Tamil Nadu and Andhra Pradesh. The coastline of the state witnessed isolated heavy rainfall and scattered light to moderate rainfall in the past 24 hours. Accordingly, the onset of the northeast monsoon has been announced for the state today. This is one of the earliest onsets of the monsoon in the last few decades. The active onset of the monsoon, as such, is around 15th October, +/- one week. Over the last three years, the onset has occurred on 15th or 16th October. Prior to that, the onset date was dominated by the fag end of the month, anytime between 25th and 30th October. Since 2010, the earliest onset was in 2024 and 2026 (15 Oct), and the most delayed onset was in 2018 (01 Nov).

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The northeast monsoon is the chief rainy season for the state of Tamil Nadu. Out of 943.7 mm of annual rainfall, the four-month-long southwest monsoon receives an average of 35%, and the three-month-long northeast monsoon gets about 48% of yearly rainfall. The northeast monsoon supports the sowing and growth of Rabi crops. Crops like rice, pulses, and maize depend heavily on these rains. The capital city, Chennai, relies heavily on these three months to fill local lakes, tanks, and reservoirs. Without a good monsoon, the state faces a severe shortage of drinking water, and the underground water table depletes too. These rains gain more importance this season because the southwest monsoon had remained deficient, with an overall shortfall of 20% rainfall.

The northeast monsoon is likely to start on a rainy note for the state. Last year, it was a mild start and improved later. There was isolated heavy rainfall on Wednesday, wherein Nagapattinam and Karaikal recorded rainfall of 91 mm and 76 mm, respectively. Today again, Karaikal is receiving heavy rainfall and has registered 56 mm of rainfall between 8:30 a.m. and 2:30 p.m. There is an active cyclonic circulation over the Gulf of Mannar and adjoining southwest Bay of Bengal, off the South Tamil Nadu coast. The coastline and the interiors are going to receive good rainfall for the next four days. Light to moderate rainfall will continue for the subsequent 3–4 days.

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