South India's Northeast Monsoon 2026: What to Expect and How to Prepare

What the Northeast Monsoon Is

The Northeast Monsoon, sometimes called South India's winter monsoon, is the season that replaces the southwest monsoon over the Bay of Bengal roughly every October. It is the chief source of rain for Tamil Nadu, Puducherry, parts of coastal Andhra Pradesh, southern Karnataka and Kerala, according to Ekam IAS Academy and Mongabay India.

Sources give slightly different figures for Tamil Nadu's dependence on this season: Ekam IAS Academy puts it at close to 48% of the state's annual rainfall between October and December, while Mongabay India reports that southern Tamil Nadu districts specifically receive around 50% of their annual rainfall from the Northeast Monsoon, spread over roughly 50 days. The season has been erratic in recent years: Mongabay India describes below-normal rains from 2016 to 2018, followed by extreme flooding in 2015 and again in 2023, when Tirunelveli recorded 123.9 cm of seasonal rainfall — 146% above its seasonal average — and Kayalpattinam, in Thoothukudi district, logged 94.6 cm in a single day, the highest 24-hour Northeast Monsoon total ever recorded in the state.

The 2026 Onset Outlook

IMD director general Mrutyunjay Mohapatra said the Northeast Monsoon is likely to commence over Tamil Nadu between October 15 and 21, 2026, according to DT Next. Separately, the private weather-tracking group Chennai Rains (COMK) reported on October 12 that a cyclonic circulation over the Andaman Sea was expected to move into the Bay of Bengal and develop into a low-pressure area, the kind of system IMD typically waits for before declaring onset, and said an official announcement around October 15–16 looked likely.

IMD's seasonal outlook, summarised by Superprep, classifies the 2026 Northeast Monsoon as 'normal' for Tamil Nadu, with a state seasonal average near 44 cm. Coastal and southern districts are expected to see normal-to-above-normal rainfall, while north interior districts may stay below normal. The outlook attributes the regional split partly to El Niño conditions and a neutral Indian Ocean Dipole.

A Short-Range Example From Early October 2026

Before the main monsoon's onset, Tamil Nadu already saw scattered pre-monsoon activity. On October 10, Polimer News reported that hill areas of Coimbatore, the Nilgiris and Theni district could see heavy rain with thunder, lightning and strong winds, while Dindigul, Virudhunagar, Madurai, Sivagangai, Ramanathapuram, Thoothukudi, Tirunelveli, Tenkasi and Kanyakumari districts were forecast scattered moderate showers. The next day's outlook pointed to isolated moderate rain in the Nilgiris, Coimbatore, Dindigul, Virudhunagar and Madurai, while the meteorological centre also warned that daytime temperatures in north interior Tamil Nadu could run up to 3°C above normal in places through October 14.

Reading IMD's Colour-Coded Alerts

IMD communicates short-term risk through four colours — green, yellow, orange and red — based on expected 24-hour rainfall and potential impact, as explained by Outlook Traveller. The colour assigned follows a matrix that weighs both the probability of an event and its likely impact over a forecasting period of up to five days, per Outlook Traveller.

A real-world example of how alerts cascade came during the 2025 Northeast Monsoon: The News Minute reported that a low-pressure system forming over the southeast Bay of Bengal led RMC Chennai to place seven districts — Ramanathapuram, Pudukkottai, Mayiladuthurai, Nagapattinam, Tiruvarur, Thanjavur and Cuddalore — under orange alert for extremely heavy rain on one day, before the warning spread to Chennai and several neighbouring districts over the following days.

How to Prepare

1. Check RMC Chennai/IMD district bulletins and colour codes daily from mid-October through December; IMD's alert matrix weighs probability and impact over a forecasting period of up to five days, per Outlook Traveller.
2. In coastal and delta districts such as Thanjavur, Nagapattinam, Tiruvarur, Cuddalore and Ramanathapuram, and in Chennai, clear local drains and move valuables out of basements or low-lying storage before an orange or red alert, given recurring urban waterlogging described by Ekam IAS Academy.
3. In hill areas like the Nilgiris and Coimbatore's mountain tracts, avoid non-essential travel during thunderstorm or strong-wind warnings, as issued for these areas by RMC Chennai per Polimer News.
4. After heavy spells, drain stagnant water quickly; Ekam IAS Academy notes that waterlogging after the Northeast Monsoon has been linked to dengue, malaria, Japanese encephalitis, leptospirosis and scrub typhus cases.
5. Farmers in monsoon-dependent delta and interior areas should follow announcements on dam-release coordination between Tamil Nadu and Kerala and consider flood-tolerant crop varieties where authorities recommend them, Ekam IAS Academy advises.
6. Use short-range 'nowcasts' — three-hour forecasts from RMC Chennai and radar-based alert tools such as the COMK Rainfall Nowcast service highlighted by Chennai Rains — for last-minute warnings once a spell is already underway.
7. Plan flexibly rather than assuming an 'average' season: Mongabay India notes the Northeast Monsoon swung from deficit years (2016–2018) to record-breaking excess (2015, 2023) within less than a decade.