Northeast monsoon sets in over Tamil Nadu; rain till 21 Oct

The northeast monsoon, which brings most of Tamil Nadu's rain each year, set in on 15 October 2026 over Tamil Nadu, Puducherry and Karaikal, coastal Andhra Pradesh, Rayalaseema, south interior Karnataka, and Kerala and Mahe, the India Meteorological Department (IMD) said. Fairly widespread to widespread rain is forecast across the region through the coming week, with isolated heavy rain in Tamil Nadu, Kerala and Puducherry until 21 October.

The onset came on the first day of the 15 to 21 October window that the IMD had forecast at the start of the month.

Key points

• Onset: 15 October 2026, over Tamil Nadu, Puducherry, Karaikal, coastal Andhra Pradesh, Rayalaseema, south interior Karnataka, Kerala and Mahe.
• Widespread rain over Tamil Nadu, Puducherry and Karaikal from 15 to 19 October; isolated heavy rain until 21 October.
• Kerala, Lakshadweep and south interior Karnataka: rain until 21 October; coastal Andhra Pradesh: 18 to 20 October.
• Strong surface winds along coastal Andhra Pradesh until at least 19 October.
• The IMD expects normal rain for Tamil Nadu this season, and has flagged a possibly higher cyclone risk because of El Niño.

Northeast monsoon 2026: where it's raining, and when

The IMD's forecast for the week, as reported by The Week:

• Tamil Nadu, Puducherry and Karaikal: fairly widespread to widespread rain from 15 to 19 October, with isolated heavy falls until 21 October.
• Kerala, Mahe, Lakshadweep and south interior Karnataka: rain from 15 to 21 October.
• Coastal Karnataka: 16 to 21 October; north interior Karnataka: 17 to 20 October.
• Rayalaseema: 16 to 20 October; coastal Andhra Pradesh and Yanam: 18 to 20 October, with strong winds.

A cyclonic circulation over the south-east Arabian Sea, off the Kerala coast, has been driving rain over the southern peninsula, the IMD said.

What the northeast monsoon is

India has two monsoons. The south-west monsoon, from June to September, brings rain to most of the country. The northeast monsoon, from October to December, is driven by winds that reverse direction in autumn and carry moisture from the Bay of Bengal onto the south-east coast.

For Tamil Nadu, it's the main rainy season, providing roughly half of the state's annual rainfall. Chennai's water supply, its reservoirs and farmers across the Cauvery delta depend on it. It also brings risk: cyclones in the Bay of Bengal and flooding in Chennai have caused major damage in several recent years.

The cyclone outlook

The IMD has said the season's rain is likely to be normal in Tamil Nadu. It has also noted that a strong El Niño, the periodic warming of the Pacific that affects weather worldwide, could raise the chance of cyclones moving towards the coasts of Tamil Nadu, Puducherry, southern Andhra Pradesh and Sri Lanka.

A low-pressure area expected over the South Andaman Sea and south-west Bay of Bengal was forecast to stay at low latitudes, which may limit its chances of developing into a cyclonic storm, the private forecaster Skymet said on 12 October. Watch the IMD's daily bulletins for updates.

Why it matters: The northeast monsoon decides whether Chennai has enough water for the next year, and whether farmers in the Cauvery delta can grow their winter rice crop. For readers in the Gulf, the UK and North America with family in Tamil Nadu and Kerala, it's also the season of school closures, flooded roads and power cuts at home.

Chennai has learned to read the sky in October, with its reservoirs low and its memories of 2015 still sharp. The rain is welcome. What the city wants this year is rain that arrives steadily, not all at once.