September is one of the warmer months of the year in Sarnia, with average highs near 21.9°C and lows around 12.4°C (mean 17.2°C). It is a relatively wet time of year, averaging 83 mm of rainfall and 75% relative humidity across the period.
September is one of the warmer months of the year in Sarnia. Across 45 years of records, the warmest Septembers in Sarnia were 2002 and 2024 — when the month averaged 19.7°C — while the coldest was 1993 at 13.5°C. Typical September days reach 21.9°C with nights near 12.4°C. The long-term trend is warming, about 0.9°C per decade.
September is a relatively wet time of year in Sarnia, averaging 83 mm of rainfall. The wettest September on record was 1986 with 251 mm, while the driest was 1991 at 18 mm.
Relative humidity in Sarnia during September averages 75%. The most humid September was 1986 at 82%, and the least humid was 1999 at 66%.
September receives about 4.2 kWh/m²/day of solar energy in Sarnia. The sunniest Septembers were 1999, 2004 and 2025 at 4.8 kWh/m²/day, and the cloudiest was 1993 at 3.2.
Average wind speed in Sarnia during September is 3 m/s. The windiest September was 2010 at 3.8 m/s, while the calmest was 2025 at 2.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 15.6°C | 16.2°C | 17.8°C | 18.0°C | 18.5°C | +2.9°C |
| Avg High | 20.3°C | 21.1°C | 22.6°C | 22.4°C | 23.3°C | +3°C |
| Avg Low | 10.9°C | 11.3°C | 12.9°C | 13.5°C | 13.7°C | +2.8°C |
| Avg Rain | 116 mm | 75 mm | 74 mm | 79 mm | 65 mm | -52 mm |
September temperatures in Sarnia have risen by about 3.4°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 0.6°C (1991) to a record high of 32.3°C (2002).
Rainfall in September is a relatively wet time of year, averaging 83 mm, with a wettest year of 251 mm.
One of the best times to visit Sarnia
September is one of the best times to visit Sarnia. Expect days averaging 21.9°C and nights around 12.4°C (mean 17.2°C) — warmer than Sarnia's yearly average — with higher rainfall (83 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 24.4°C | 19.0°C | 13.5°C | 27.9°C | 8.1°C | 33 mm | 69% | 2.2 m/s | 4.8 |
| 2024 | 24.8°C | 19.7°C | 14.7°C | 28.4°C | 7.9°C | 37 mm | 72% | 2.7 m/s | 4.4 |
| 2023 | 22.8°C | 18.3°C | 13.8°C | 30.4°C | 9.9°C | 77 mm | 77% | 2.5 m/s | 4 |
| 2022 | 23.1°C | 18.5°C | 14.0°C | 29.9°C | 8.3°C | 34 mm | 72% | 2.9 m/s | 4.1 |
| 2021 | 22.9°C | 18.2°C | 13.5°C | 28.4°C | 7.9°C | 155 mm | 75% | 3.5 m/s | 4.4 |
| 2020 | 21.9°C | 17.2°C | 12.5°C | 27.5°C | 5.9°C | 51 mm | 76% | 3.5 m/s | 4.3 |
| 2019 | 23.2°C | 18.8°C | 14.4°C | 28.2°C | 10.8°C | 115 mm | 80% | 3 m/s | 4 |
| 2018 | 23.5°C | 19.2°C | 15.0°C | 30.7°C | 6.1°C | 47 mm | 79% | 3.1 m/s | 3.8 |
| 2017 | 23.1°C | 18.3°C | 13.5°C | 30.3°C | 7.9°C | 41 mm | 77% | 2.5 m/s | 4.5 |
| 2016 | 23.9°C | 19.4°C | 14.8°C | 30.0°C | 9.8°C | 66 mm | 76% | 3 m/s | 4.4 |
| 2015 | 24.0°C | 19.6°C | 15.3°C | 30.0°C | 9.0°C | 71 mm | 77% | 2.8 m/s | 4.5 |
| 2014 | 21.2°C | 16.6°C | 11.9°C | 28.9°C | 6.0°C | 115 mm | 79% | 2.8 m/s | 4.3 |
| 2013 | 21.4°C | 16.8°C | 12.2°C | 31.1°C | 5.9°C | 53 mm | 76% | 3 m/s | 4.4 |
| 2012 | 21.5°C | 16.8°C | 12.1°C | 30.0°C | 4.5°C | 64 mm | 72% | 3.1 m/s | 4.4 |
| 2011 | 21.2°C | 17.0°C | 12.9°C | 30.6°C | 6.8°C | 109 mm | 80% | 3.1 m/s | 3.6 |
| 2010 | 21.4°C | 17.0°C | 12.5°C | 30.9°C | 8.1°C | 108 mm | 73% | 3.8 m/s | 4 |
| 2009 | 22.3°C | 17.8°C | 13.3°C | 26.1°C | 6.0°C | 39 mm | 75% | 2.7 m/s | 4.5 |
| 2008 | 22.7°C | 18.1°C | 13.4°C | 30.6°C | 10.1°C | 149 mm | 77% | 2.7 m/s | 4.3 |
| 2007 | 24.0°C | 18.8°C | 13.7°C | 30.3°C | 6.6°C | 37 mm | 72% | 3 m/s | 4.6 |
| 2006 | 20.5°C | 16.1°C | 11.7°C | 26.9°C | 4.8°C | 67 mm | 78% | 3.4 m/s | 3.5 |
| 2005 | 24.6°C | 19.5°C | 14.3°C | 30.7°C | 7.5°C | 79 mm | 71% | 3.3 m/s | 4.5 |
| 2004 | 23.7°C | 18.9°C | 14.1°C | 27.5°C | 8.5°C | 23 mm | 73% | 3 m/s | 4.8 |
| 2003 | 21.7°C | 16.6°C | 11.4°C | 28.4°C | 3.8°C | 92 mm | 71% | 3.1 m/s | 4.5 |
| 2002 🔥 | 25.2°C | 19.7°C | 14.2°C | 32.3°C | 7.6°C | 35 mm | 69% | 3 m/s | 4.7 |
| 2001 | 20.4°C | 15.8°C | 11.2°C | 27.7°C | 3.7°C | 111 mm | 76% | 3.4 m/s | 4.3 |
| 2000 | 20.9°C | 16.4°C | 12.0°C | 30.1°C | 5.9°C | 110 mm | 76% | 3.7 m/s | 4 |
| 1999 | 23.4°C | 17.8°C | 12.3°C | 29.7°C | 5.7°C | 70 mm | 66% | 3.1 m/s | 4.8 |
| 1998 | 24.4°C | 19.4°C | 14.4°C | 30.7°C | 9.2°C | 37 mm | 68% | 3.1 m/s | 4.6 |
| 1997 | 21.2°C | 16.6°C | 12.0°C | 26.5°C | 6.9°C | 79 mm | 76% | 3.3 m/s | 4.1 |
| 1996 | 20.4°C | 16.3°C | 12.2°C | 28.0°C | 6.2°C | 155 mm | 80% | 3.1 m/s | 3.8 |
| 1995 | 20.5°C | 15.1°C | 9.8°C | 28.5°C | 1.1°C | 24 mm | 68% | 2.9 m/s | 4.4 |
| 1994 | 21.6°C | 16.5°C | 11.4°C | 27.8°C | 5.2°C | 62 mm | 74% | 2.9 m/s | 4.4 |
| 1993 ❄️ | 17.6°C | 13.5°C | 9.3°C | 25.9°C | 2.8°C | 107 mm | 78% | 2.9 m/s | 3.2 |
| 1992 | 19.9°C | 15.0°C | 10.2°C | 25.1°C | 2.8°C | 101 mm | 79% | 3.3 m/s | 4.2 |
| 1991 | 20.8°C | 15.5°C | 10.1°C | 29.2°C | 0.6°C | 18 mm | 68% | 2.9 m/s | 4.2 |
| 1990 | 20.7°C | 15.8°C | 10.9°C | 28.5°C | 4.3°C | 95 mm | 76% | 3.1 m/s | 4.1 |
| 1989 | 20.1°C | 15.5°C | 11.0°C | 26.4°C | 1.5°C | 108 mm | 77% | 2.7 m/s | 4.1 |
| 1988 | 21.5°C | 16.3°C | 11.1°C | 27.6°C | 5.9°C | 71 mm | 73% | 3.3 m/s | 4.1 |
| 1987 | 20.6°C | 16.2°C | 11.7°C | 27.1°C | 5.5°C | 94 mm | 80% | 2.5 m/s | 4.1 |
| 1986 🌧️ | 20.7°C | 15.7°C | 10.8°C | 24.7°C | 3.0°C | 251 mm | 82% | 2.8 m/s | 3.9 |
| 1985 | 20.5°C | 16.0°C | 11.6°C | 28.2°C | 3.7°C | 104 mm | 80% | 2.9 m/s | 4.1 |
| 1984 | 18.7°C | 14.0°C | 9.3°C | 28.2°C | 3.9°C | 92 mm | 77% | 2.8 m/s | 3.9 |
| 1983 | 21.7°C | 16.3°C | 10.9°C | 29.9°C | 2.5°C | 71 mm | 72% | 2.9 m/s | — |
| 1982 | 20.0°C | 15.1°C | 10.2°C | 27.2°C | 4.0°C | 73 mm | 79% | 2.6 m/s | — |
| 1981 | 19.1°C | 15.1°C | 11.2°C | 26.5°C | 4.0°C | 185 mm | 79% | 3.2 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 21.9°C with lows near 12.4°C (mean 17.2°C), based on 45 years of NASA POWER data.
September averages 83 mm of rainfall in Sarnia, a relatively wet time of year. The wettest on record was 251 mm in 1986.
The hottest September reached 32.3°C in 2002. The coldest dipped to 0.6°C in 1991.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 3.4°C. Daytime highs moved from 20°C to 23.6°C and overnight lows from 10.6°C to 13.9°C over the same span.
September is one of the warmer months of the year in Sarnia and a relatively wet time of year, so plan for around 21.9°C daytime highs and 12.4°C at night.
Not quite — September is the 9th coolest month in Sarnia, averaging 17.2°C.
For September in Sarnia, pack light layers you can adjust through the day, with typical highs of 21.9°C and lows of 12.4°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 75% — quite humid.
Average wind speed in September is 3 m/s. The windiest September on record averaged 3.8 m/s (2010).
The wettest September on record was 1986 with 251 mm. On average, September sees 83 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Sarnia behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
