While a strong El Niño expected in 2026 usually weakens rainfall across much of India, Tamil Nadu could see the opposite: heavy northeast monsoon rain and cyclones, fed by moist Bay of Bengal winds and warmer seas. El Niño refers to abnormal warming of Pacific surface waters off Peru and Ecuador that alters weather worldwide. In the 2015 El Niño, Chennai received 1,522 mm of rain in four days (1–4 December), leading to severe floods. Satellites showed the southern Bay of Bengal about 1°C warmer than normal in September 2026. The Indian Ocean Dipole (IOD), a sea-temperature contrast between the western and eastern equatorial Indian Ocean, also influences rainfall.