Northeast monsoon onset 2026: Chennai rain forecast for 14 to 21 October
Published
IMD's onset window over Tamil Nadu is 15 to 21 October, with normal to above-normal rain expected. Chennai starts dry: 0 mm at Nungambakkam this October against a 300 mm average, Skymet said.
Original report
The Chennai rain forecast for 14 to 21 October is a week-long wet spell as the northeast monsoon onset nears, Skymet Weather said on 13 October 2026 (Skymet Weather, 2026). The India Meteorological Department (IMD) put the onset window over Tamil Nadu at 15 to 21 October, with onset expected around 15 October if conditions hold, DT Next reported (DT Next, 2026b; DT Next, 2026c).
Rain was forecast to reach Chennai and the northern coastal districts from the afternoon of 14 October, DT Next reported (DT Next, 2026c).
The season starts from a low base. Nungambakkam had recorded 0 mm of rain in October up to 13 October, Skymet said, against a long-term October average of 300 mm (Skymet Weather, 2026). Here is the forecast, day by day, and what it means.
IMD's onset window runs from 15 to 21 October
IMD said in its seasonal outlook, reported on 1 October 2026, that the northeast monsoon would likely begin over Tamil Nadu between 15 and 21 October, DT Next reported (DT Next, 2026b).
The outlook, given by IMD Director General Dr M Mohapatra, expects normal to above-normal rain for south India and the adjoining coast (DT Next, 2026b).
The window has since narrowed. DT Next reported on 12 October that onset was likely around 15 October, if a low-pressure system expected over the Bay of Bengal within 24 hours formed (DT Next, 2026c).
That timing depends on the old monsoon leaving first.
The southwest monsoon exits by 15 October
The southwest monsoon was expected to withdraw completely by 15 October, DT Next reported on 14 October 2026 (DT Next, 2026a).
It leaves behind a shortfall. The southwest monsoon ended with a 20% rainfall deficit, Skymet Weather said on 13 October (Skymet Weather, 2026).
For Chennai, the new season is the one that counts. "October and November are the rainiest months for Chennai," said AVM GP Sharma of Skymet Weather (Skymet Weather, 2026).
The numbers show how much rain the city usually counts on.
Chennai normally gets 674 mm in October and November
Skymet puts Chennai's long-term average at 300 mm in October and 374 mm in November (Skymet Weather, 2026). Added together, that is 674 mm across the two months.
This October has barely started. Nungambakkam had 0 mm so far, and Minambakkam recorded 5 mm on 5 October, Skymet said on 13 October (Skymet Weather, 2026).
So the city needs close to its full monthly average in under three weeks to reach a normal October. That arithmetic uses Skymet's 300 mm figure and the 0 mm recorded at Nungambakkam.
The coming week is where that starts.
Heavy rain is forecast from 16 to 20 October
IMD forecast isolated heavy rain over Tamil Nadu, Puducherry and Karaikal on 14 October and again from 16 to 20 October, DT Next reported (DT Next, 2026a).
Chennai may see a spell from 14 to 21 October, heaviest at night and in the early morning, with thunderstorms and gusty winds likely, Skymet said (Skymet Weather, 2026).
For commuters, that points to wet nights and mornings rather than all-day rain. The independent blogger Tamil Nadu Weatherman described the pattern to DT Next as intermittent spells of rain and sunshine, typical of the northeast monsoon (DT Next, 2026a).
One risk looks lower this year.
A strong El Nino lowers the cyclone risk
El Nino is in a strong phase through December, which IMD's Director General said lowers the chance and strength of cyclones, DT Next reported on 1 October (DT Next, 2026b).
The state is also adding equipment. IMD and Tamil Nadu plan four new weather radars and 1,000 more rain gauges, on top of 1,400 already in place, DT Next reported (DT Next, 2026b). That would take the network to 2,400 gauges.
What we don't know yet
- Whether IMD formally declares onset on 15 October.
- Which district colour alerts are in force: we did not open IMD's district warning pages.
- IMD's seasonal rainfall figure as a percentage of the long-period average.
Questions people are asking
When will the northeast monsoon start in Tamil Nadu in 2026?
IMD's window is 15 to 21 October, with onset expected around 15 October if conditions hold (DT Next, 2026b; DT Next, 2026c).
Will Chennai get heavy rain this week?
Skymet expects a rain spell from 14 to 21 October, and IMD forecast isolated heavy rain from 16 to 20 October (Skymet Weather, 2026; DT Next, 2026a).
Will there be a cyclone this northeast monsoon?
IMD's Director General said a strong El Nino lowers the likelihood and intensity of cyclones (DT Next, 2026b).
Will the northeast monsoon rain be normal in 2026?
IMD expects normal to above-normal rain for south India and the adjoining coast (DT Next, 2026b).
References
- DT Next (2026a) Chennai, districts receive showers as northeast monsoon onset nears; heavy rain forecast across TN. DT Next. Available at: Chennai, districts receive showers as northeast monsoon onset nears; heavy rain forecast across TN (Accessed: 14 October 2026).
- DT Next (2026b) Northeast monsoon may begin between October 15-21: IMD. DT Next. Available at: Northeast monsoon may begin between October 15-21: IMD (Accessed: 14 October 2026).
- DT Next (2026c) Northeast monsoon likely to begin in Tamil Nadu, Puducherry on October 15. DT Next. Available at: Northeast monsoon likely to begin in Tamil Nadu, Puducherry on October 15 (Accessed: 14 October 2026).
- Skymet Weather (2026) Rainy Days For Chennai Ahead: Onset of Northeast Monsoon Soon. Skymet Weather Services. Available at: Rainy Days For Chennai Ahead: Onset of Northeast Monsoon Soon (Accessed: 14 October 2026).
How we did this
We built a day-by-day forecast timeline from IMD's seasonal outlook as reported by DT Next on 1 October, DT Next's onset reports of 12 October and 14 October, and Skymet Weather's Chennai update of 13 October. We set Chennai's October rain so far against Skymet's long-term averages, and show our arithmetic. We did not open IMD's district warning pages, so this story gives no district colour alerts.
This story was produced, reviewed, edited and verified by the reporter before publication, with AI assistance where required.
Covered by 4 outlets across the spectrum: 75% left, 0% center, 0% right.
Who is covering this story
- Left-leaning (1): DT Next
- Not yet rated (1): Skymet Weather
Sources
- Chennai, districts receive showers as northeast monsoon onset nears; heavy rain forecast across TN — DT Next (left-leaning) ·
- Northeast monsoon likely to begin in Tamil Nadu, Puducherry on October 15 — DT Next (left-leaning) ·
- Northeast monsoon may begin between October 15-21: IMD — DT Next (left-leaning) ·
- Rainy Days For Chennai Ahead: Onset of Northeast Monsoon Soon — Skymet Weather (not yet rated) ·