Chennai’s hottest months on average are May and June, not April. IMD’s 1991-2020 normals for Nungambakkam put the mean daily maximum at 37.3°C in May and 37.2°C in June, against 34.7°C in April. The coolest nights come in January, when the mean minimum is 21.5°C.
Those averages hide wide swings. This piece puts the official normals, recent monthly extremes and the October record book side by side, so you can see what counts as unusual heat in Chennai and when IMD would call it a heat wave.
The 30-year normals, month by month
The Regional Meteorological Centre in Chennai publishes a climatological table for Nungambakkam, the city’s reference observatory, based on 1991-2020 data. Daily maximum and minimum temperatures averaged over each month look like this:
| Month | Mean max (°C) | Mean min (°C) |
|---|---|---|
| January | 29.7 | 21.5 |
| February | 31.2 | 22.4 |
| March | 33.1 | 24.5 |
| April | 34.7 | 26.9 |
| May | 37.3 | 28.2 |
| June | 37.2 | 27.9 |
| July | 35.7 | 26.8 |
| August | 34.9 | 26.2 |
| September | 34.3 | 25.8 |
| October | 32.6 | 25.0 |
| November | 30.3 | 23.5 |
| December | 29.4 | 22.2 |
| Annual | 33.4 | 25.1 |
The same table counts thunder days, which track the heat: Nungambakkam averages 34.1 days with thunder a year, peaking at 7.0 in October and 6.2 in September, when hot, humid afternoons build storm clouds. October also averages 10.5 rainy days.
Note how warm the nights are from May to July. A mean minimum above 28°C in May is why the city rarely cools down after sunset in early summer, and why the sea breeze timing matters so much to how a day feels.
Recent extremes: Nungambakkam and Meenambakkam
The state’s Statistical Hand Book 2022-23, quoting the Regional Meteorological Centre, lists the highest and lowest temperatures recorded each month at both Chennai stations. Meenambakkam, at the airport and further from the sea, usually runs hotter by day and cooler at night.
| Measure (June 2022 to May 2023) | Nungambakkam | Meenambakkam |
|---|---|---|
| Highest maximum (May 2023) | 41.8°C | 42.7°C |
| Highest maximum (June 2022) | 40.1°C | 40.3°C |
| Lowest minimum (January 2023) | 19.5°C | 18.4°C |
| Lowest minimum (December 2022) | 19.8°C | 19.2°C |
In the previous year (June 2021 to May 2022), the peak was 39.9°C at both stations in June 2021, and Meenambakkam’s lowest reading was 18.4°C in December 2021.
The 2026 summer was also harsh. A UNI report of 21 May 2026 said Meenambakkam touched about 42°C (107.6°F) on 20 May, the season’s highest, with Nungambakkam at 105.6°F, roughly 40.9°C.
October: the record book for this month
With the northeast monsoon under way, October is a transition month. IMD’s station tables give October extremes for the last ten years and the all-time October records.
| October record | Nungambakkam | Meenambakkam |
|---|---|---|
| All-time highest maximum | 39.4°C (1 Oct 1920) | 39.4°C (1 Oct, year not given) |
| All-time lowest minimum | 16.7°C (28 Oct 1889) | 19.6°C (31 Oct, year not given) |
| Highest in October 2025 | 35.6°C (6 Oct) | 36.1°C (6 Oct) |
| Highest in October 2024 | 37.1°C (3 Oct) | 37.1°C (3 Oct) |
| Lowest in October 2025 | 22.9°C (28 Oct) | 23.0°C (29 Oct) |
Over 2016-2025, Nungambakkam’s hottest October day never went above 37.1°C, reached in both 2020 and 2024. The Meenambakkam table shows a slightly higher 37.2°C in October 2020.
When IMD calls it a heat wave
Chennai is a coastal station, so it is judged by a different rule from inland towns. IMD’s heat wave definitions say a coastal station can be described as under heat wave when the maximum is at least 4.5°C above normal and the actual reading is 37°C or more. For plains stations the bar is a maximum of at least 40°C, with heat wave declared at 4.5°C to 6.4°C above normal, or at 45°C regardless of the normal.
In both cases the criteria must hold at two or more stations in a meteorological subdivision for at least two days in a row; IMD declares the heat wave on the second day. Using the May normal of 37.3°C, a Nungambakkam reading of about 41.8°C or more would meet the departure test.
Practical takeaways
- Plan outdoor work, construction shifts and school sports for early mornings from late April to June, when both day and night temperatures peak.
- Expect the airport (Meenambakkam) to report the higher number on most hot afternoons; news headlines usually quote it.
- For live readings and warnings, use the IMD Chennai site and the Mausam app rather than forwarded messages.
Heat illness can turn serious quickly; anyone with dizziness, confusion or stopped sweating should get medical help, or call 108.
Quick answers
What is the hottest month in Chennai?
May, with a mean daily maximum of 37.3°C at Nungambakkam (1991-2020 normals), closely followed by June at 37.2°C.
What is Chennai’s coldest month?
January, with a mean minimum of 21.5°C.
What is the hottest October day on record in Chennai?
39.4°C at Nungambakkam on 1 October 1920, per IMD.
What is a heat wave for Chennai?
At least 37°C and 4.5°C or more above normal, at two stations for two consecutive days.
Information checked against official sources on 18 October 2026. Fees, dates and rules can change; confirm on the linked official pages before acting.
Sources
- Chennai (Nungambakkam): October extremes and climatological table 1991-2020 (IMD Regional Meteorological Centre, Chennai)
- Chennai (Meenambakkam): October extremes and climatological table 1991-2020 (IMD Regional Meteorological Centre, Chennai)
- Statistical Hand Book of Tamil Nadu 2022-23, Chapter 3: Climate and Rainfall (Department of Economics and Statistics, Government of Tamil Nadu)
- Heat wave and cold wave definitions (India Meteorological Department)
- TN sizzles under oppressive heat, season’s high of 108 deg F scorches Chennai (UNI, 21 May 2026)
