October brings Chennai an average of 300.3 mm of rain over about 10.5 rainy days, based on the India Meteorological Department’s 1991-2020 normal for Nungambakkam. Over the past ten years, though, the city’s October total has ranged from just 22.4 mm in 2016 to 390.0 mm in 2024, so the “average October” is something residents rarely actually get.
With the northeast monsoon setting in on 15 October 2026, here is how the last ten Octobers played out at the city’s two IMD observatories, Nungambakkam in the city centre and Meenambakkam at the airport, taken from IMD Chennai’s monthly record sheets.
Ten Octobers at Nungambakkam
The Nungambakkam sheet lists each October’s total and its wettest single day:
| Year | October total (mm) | Wettest day (mm, date) |
|---|---|---|
| 2025 | 324.3 | 97.9 (22 Oct) |
| 2024 | 390.0 | 142.9 (16 Oct) |
| 2023 | 109.5 | 25.6 (21 Oct) |
| 2022 | 171.0 | 30.3 (21 Oct) |
| 2021 | 216.4 | 34.0 (30 Oct) |
| 2020 | 318.5 | 133.4 (29 Oct) |
| 2019 | 318.2 | 101.6 (18 Oct) |
| 2018 | 162.2 | 53.4 (5 Oct) |
| 2017 | 294.7 | 116.4 (31 Oct) |
| 2016 | 22.4 | 10.2 (1 Oct) |
Only four of the ten Octobers (2019, 2020, 2024 and 2025) beat the 300.3 mm normal, and two of those only just. The simple ten-year average works out to about 233 mm, well below the 30-year normal. That gap is a reminder that a few very wet Octobers, above all 2005, pull the long-term mean up.
The airport often sees a different month
Meenambakkam is about 12 km south-west of Nungambakkam, and the two stations can record very different totals in the same month. From the Meenambakkam sheet:
| Year | Meenambakkam total (mm) | Nungambakkam total (mm) |
|---|---|---|
| 2025 | 396.5 | 324.3 |
| 2024 | 286.2 | 390.0 |
| 2023 | 49.8 | 109.5 |
| 2022 | 187.8 | 171.0 |
| 2021 | 187.0 | 216.4 |
| 2020 | 158.2 | 318.5 |
| 2019 | 313.5 | 318.2 |
| 2018 | 257.2 | 162.2 |
| 2017 | 348.5 | 294.7 |
| 2016 | 5.9 | 22.4 |
In 2020 the city centre got about twice the airport’s October rain. In 2018 and 2025 it was the other way round. For residents, the practical lesson is that “Chennai got X mm” usually means Nungambakkam, and your own street in Tambaram or Porur may have had a quite different month.
Records and extremes
- Wettest October on record at Nungambakkam: 1,077.8 mm, in 2005.
- Heaviest October day at Nungambakkam: 279.7 mm, in 1969.
- Heaviest October day at Meenambakkam: 229.6 mm, on the 10th of the month, per IMD’s sheet.
- Wettest October at Meenambakkam: 799.7 mm.
- Driest recent October: 2016, with 22.4 mm in the city and 5.9 mm at the airport, the year the northeast monsoon largely failed.
The heaviest October day in the last decade at either station was 168.7 mm at Meenambakkam on 31 October 2017, more than half of a normal month’s rain in 24 hours.
Heavy days decide the month
The wettest single day often supplies a large share of an October’s rain. In 2024, the 142.9 mm that fell at Nungambakkam on 16 October was more than a third of that month’s 390.0 mm. In 2020, 133.4 mm on 29 October made up about 42% of the month. In 2017, 116.4 mm fell on 31 October, nearly 40% of the total. By contrast, in the dry Octobers of 2022 and 2023 no day brought more than about 30 mm.
The dates also matter. In six of the ten years, the wettest October day at Nungambakkam fell after the 20th, which fits the usual onset of the northeast monsoon in the second half of the month.
Heat lingers into October
October is not yet cool. The airport recorded daytime highs of 35.5 to 37.2°C in every October from 2016 to 2025, usually in the first half of the month before the rains set in. Night-time lows rarely dropped below 22°C, with the coolest October night of the decade at 20.0°C on 25 October 2022.
How October fits the season
The state statistical handbook puts Chennai district’s northeast monsoon normal at 809.6 mm for October to December, so October normally supplies a bit over a third of the season’s rain. A dry October does not mean a dry season: 2023 had a weak October and then Cyclone Michaung in early December.
For the days ahead, IMD Chennai’s seven-day district bulletin, issued on 17 October 2026, flagged heavy rain at isolated places over Chennai on some days of the week.
Quick answers
How much rain does Chennai get in October?
The 1991-2020 normal at Nungambakkam is 300.3 mm over about 10.5 rainy days.
Which recent October was wettest?
2024 at Nungambakkam (390.0 mm) and 2025 at Meenambakkam (396.5 mm).
What is the October record?
1,077.8 mm at Nungambakkam in October 2005.
Where can I see daily rainfall?
IMD Chennai’s website (mausam.imd.gov.in/chennai) posts daily station rainfall and district warnings.
Information checked against official sources on 18 October 2026. Fees, dates and rules can change; confirm on the linked official pages before acting.
Sources
- Extreme Weather Events in the Month of October, Chennai Nungambakkam (IMD Regional Meteorological Centre, Chennai)
- Extreme Weather Events in the Month of October, Chennai Meenambakkam (IMD Regional Meteorological Centre, Chennai)
- Statistical Hand Book of Tamil Nadu 2022-23, Climate and Rainfall (Department of Economics and Statistics)
- 7-day district forecast bulletin, 17 October 2026 (IMD Regional Meteorological Centre, Chennai)
