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Northeast monsoon 2026 arrives in Tamil Nadu: onset, rain forecast and what to expect in Chennai
The northeast monsoon 2026 is setting in over Tamil Nadu from 15 October. IMD expects normal October to December rain. Forecast, warnings and Chennai outlook.
By the Good Air team
In this article · 6 sections
The northeast monsoon 2026 is setting in over Tamil Nadu and the southern peninsula from 15 October, as the southwest monsoon withdraws from the rest of India, according to the India Meteorological Department (IMD) (News Today, 15 October). IMD expects October to December rainfall over South Peninsular India to be normal, 88% to 112% of the long-term average, and has warned of heavy to very heavy rain at isolated places in Tamil Nadu this week (IMD press release, 30 September).
For Tamil Nadu this is the season that matters most. Tamil Nadu, Puducherry and Karaikal get about 48% of their yearly rainfall from October to December (IMD, 30 September).
When does the northeast monsoon start in 2026?
The northeast monsoon is the October to December rainy season of south-east India. In summer, the wind blows from the south-west and drops rain on most of India. From mid-October it turns round and blows from the north-east, picking up moisture over the Bay of Bengal and bringing rain to Tamil Nadu, Puducherry, coastal Andhra Pradesh, south interior Karnataka and Kerala.
IMD Director-General Mrutyunjay Mohapatra had said onset conditions would be favourable from the third week of October (The Hindu via SuperPrep, 1 October). By 15 October, IMD said conditions had become favourable for the northeast monsoon to begin over the southern peninsula that day.
What is not yet confirmed: as of the morning of 15 October 2026, we had not seen IMD's formal onset announcement in its daily bulletin. IMD usually declares onset once rain and north-easterly winds are established over the region. We will update this article when it does.
How much rain will Tamil Nadu get this season?
IMD's seasonal outlook, issued on 30 September 2026, says:
- South Peninsular India, October to December: most likely normal, 88% to 112% of the long period average (LPA). The LPA for the season is about 334.1 mm, based on 1971 to 2020.
- Within the region: southern parts of the peninsula are likely to get normal to above normal rain. Most of the rest of India is expected to be drier than normal.
- October 2026, India as a whole: below normal, under 85% of LPA.
- Temperatures: above normal maximum temperatures over most of the country in October.
IMD's forecast rests partly on the Pacific. It says strong El Niño conditions are present and likely to strengthen until the end of the year, while the Indian Ocean Dipole, a sea-temperature pattern in the Indian Ocean, is neutral. Our explainer on El Niño and winter 2026 covers what that means around the world.
The south needs the rain. The southwest monsoon gave the South Peninsula only 76% of its normal rainfall from June to September 2026, its fourth-lowest since 1901. Northwest India got 94.1%, Central India 97% and Northeast India 74%, and India as a whole got 87% (IMD, 30 September).
What is the rain forecast for Chennai?
Chennai has been dry so far this month. Nungambakkam had recorded no rain in October by 13 October, and Minambakkam just 5 mm. Chennai's normal October rainfall is about 300 mm and November's 374 mm. Skymet expects a week-long wet spell from 14 to 21 October, with the heaviest rain at night and in the early morning (Skymet, 13 October).
IMD's district warnings for Chennai, issued on 15 October and shown in Good Air's warnings feed, are yellow on every day from 15 to 20 October. Yellow means "be aware". The warning for 16 October includes heavy rain; the other days carry thunderstorms with lightning.
| Place | IMD warnings, 15 to 20 October 2026 |
|---|---|
| Chennai | Yellow every day; heavy rain on 16 October |
| Puducherry | Yellow; heavy rain on 15, 16 and 17 October |
| Coimbatore | Yellow; heavy rain on most days |
| Madurai | Yellow; heavy rain on 17, 18 and 19 October |
| Kochi, Kerala | Orange on 15 October for very heavy rain |
| Vijayawada, Tirupati, Nellore, Ongole and Anantapur, Andhra Pradesh | Orange on 16, 17 and 18 October for heavy rain and strong winds |
Source: IMD district warnings issued 15 October 2026, via Good Air's weather alerts page, which updates every day. Orange means "be prepared".
On 15 October, IMD's Chennai centre also forecast heavy to very heavy rain at isolated places in the hills of Virudhunagar, the Nilgiris, Coimbatore and Theni, with gusty winds of 40 to 50 km/h (News Today, 15 October).
Will there be a cyclone?
The northeast monsoon is also the Bay of Bengal's main cyclone season, and October to December storms often bring Tamil Nadu's heaviest rain. As of 15 October 2026, we found no IMD forecast of a cyclone for the coming days. Skymet linked this week's rain to a cyclonic circulation over the south-west Bay of Bengal and the Gulf of Mannar, a weaker system than a cyclone. Forecasts for late October and November are less certain; check IMD's bulletins before travel or fishing trips.
What does the monsoon mean for air quality?
Rain is good for the air. It washes dust and smoke out of the atmosphere, which is why south India's air is cleaner than the north's at this time of year. On 14 October 2026, CPCB's 24-hour AQI was 73 (Satisfactory) in Chennai, 52 in Coimbatore and 53 in Puducherry, while Delhi was at 181 (CPCB, 14 October). The Chennai air quality page has the live reading.
The monsoon brings other risks. Standing water after heavy rain breeds mosquitoes, and damp homes grow mould, which can trouble people with asthma.
How to prepare for heavy rain
- Check the district warning each morning. IMD's colours: yellow (be aware), orange (be prepared), red (take action).
- Avoid flooded roads and underpasses. Water hides open drains and fallen power lines.
- Stay indoors in thunderstorms. Lightning is the main danger in the yellow warnings this week.
- Keep phones charged and a torch ready in case of power cuts.
- Clear standing water around your home every few days to stop mosquitoes breeding.
- Fishermen should follow IMD's sea warnings before going out.
Frequently asked questions
When does the northeast monsoon start in 2026?
IMD said conditions were favourable for the northeast monsoon to begin over Tamil Nadu and the southern peninsula on 15 October 2026, as the southwest monsoon withdrew from the rest of India. IMD's Director-General had expected onset in the third week of October. IMD confirms onset in its daily bulletin.
Will the northeast monsoon 2026 be normal?
Yes, according to IMD's seasonal outlook of 30 September 2026. It expects October to December rainfall over South Peninsular India to be normal, 88% to 112% of the long period average of about 334.1 mm. Southern parts of the peninsula may get normal to above normal rain.
How much rain does Chennai get in October?
Chennai's normal October rainfall is about 300 mm, and November's is about 374 mm, making them the city's wettest months. By 13 October 2026, Nungambakkam had recorded no rain this October and Minambakkam just 5 mm, so the city was starting the season dry.
Why is the northeast monsoon important for Tamil Nadu?
Tamil Nadu, Puducherry and Karaikal get about 48% of their yearly rainfall during the northeast monsoon from October to December, according to IMD. Most of India gets its rain from the summer southwest monsoon, but Tamil Nadu lies in its rain shadow, so its reservoirs and farms depend on the winter rains.
Does El Niño affect the northeast monsoon?
IMD lists El Niño among the factors in its 2026 northeast monsoon outlook, alongside a neutral Indian Ocean Dipole, and still expects normal rain over the southern peninsula. India's summer monsoon ended at 87% of normal in 2026 during a strong El Niño, but El Niño's effect on the winter monsoon is less direct.
