September is one of the warmer months of the year in St. Catharines, with average highs near 21.8°C and lows around 13.9°C (mean 17.9°C). It is a relatively wet time of year, averaging 78 mm of rainfall and 73% relative humidity across the period.
September is one of the warmer months of the year in St. Catharines. Across 45 years of records, the warmest September in St. Catharines was 2016 — when the month averaged 20.9°C — while the coldest was 1993 at 14.5°C. Typical September days reach 21.8°C with nights near 13.9°C. The long-term trend is warming, about 1°C per decade.
September is a relatively wet time of year in St. Catharines, averaging 78 mm of rainfall. The wettest September on record was 1986 with 140 mm, while the driest were 2023 and 2025 at 28 mm.
Relative humidity in St. Catharines during September averages 73%. The most humid September was 1987 at 80%, and the least humid was 1991 at 66%.
September receives about 4.1 kWh/m²/day of solar energy in St. Catharines. The sunniest September was 2005 at 4.7 kWh/m²/day, and the cloudiest were 1993 and 2006 at 3.2.
Average wind speed in St. Catharines during September is 3.1 m/s. The windiest September was 2010 at 3.8 m/s, while the calmest was 2025 at 2.3 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 16.6°C | 16.3°C | 18.1°C | 19.1°C | 19.7°C | +3.1°C |
| Avg High | 20.6°C | 20.4°C | 22.0°C | 22.9°C | 23.6°C | +3°C |
| Avg Low | 12.6°C | 12.1°C | 14.1°C | 15.4°C | 15.8°C | +3.2°C |
| Avg Rain | 92 mm | 69 mm | 89 mm | 81 mm | 47 mm | -45 mm |
September temperatures in St. Catharines have risen by about 2.8°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 2.6°C (1993) to a record high of 31.1°C (2002).
Rainfall in September is a relatively wet time of year, averaging 78 mm, with a wettest year of 140 mm.
One of the best times to visit St. Catharines
September is one of the best times to visit St. Catharines. Expect days averaging 21.8°C and nights around 13.9°C (mean 17.9°C) — warmer than St. Catharines's yearly average — with moderate rainfall (78 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 | 24.1°C | 19.8°C | 15.5°C | 27.3°C | 11.5°C | 28 mm | 67% | 2.3 m/s | 4.5 |
| 2024 | 25.0°C | 20.8°C | 16.7°C | 28.6°C | 11.6°C | 50 mm | 70% | 2.6 m/s | 4.3 |
| 2023 | 23.6°C | 19.7°C | 15.9°C | 30.3°C | 12.4°C | 28 mm | 70% | 2.7 m/s | 4.4 |
| 2022 | 22.7°C | 19.2°C | 15.7°C | 29.2°C | 9.0°C | 62 mm | 71% | 3.1 m/s | 3.9 |
| 2021 | 23.7°C | 20.0°C | 16.3°C | 27.2°C | 11.7°C | 80 mm | 69% | 3.6 m/s | 4.3 |
| 2020 | 22.7°C | 18.8°C | 14.8°C | 28.3°C | 9.1°C | 35 mm | 69% | 3.6 m/s | 4.2 |
| 2019 | 23.1°C | 19.4°C | 15.6°C | 27.8°C | 13.3°C | 92 mm | 76% | 3.2 m/s | 3.8 |
| 2018 | 23.9°C | 20.5°C | 17.1°C | 30.9°C | 11.2°C | 80 mm | 75% | 3.1 m/s | 3.9 |
| 2017 | 23.7°C | 19.7°C | 15.7°C | 30.5°C | 10.5°C | 63 mm | 71% | 2.5 m/s | 4.6 |
| 2016 🔥 | 24.7°C | 20.9°C | 17.1°C | 30.2°C | 12.6°C | 58 mm | 70% | 3.2 m/s | 4.4 |
| 2015 | 24.6°C | 20.7°C | 16.8°C | 30.1°C | 12.2°C | 93 mm | 73% | 3 m/s | 4.2 |
| 2014 | 22.0°C | 18.1°C | 14.1°C | 28.7°C | 9.0°C | 71 mm | 73% | 3 m/s | 4.1 |
| 2013 | 21.3°C | 17.4°C | 13.6°C | 28.7°C | 8.6°C | 73 mm | 73% | 3.1 m/s | 4.1 |
| 2012 | 21.9°C | 18.1°C | 14.4°C | 30.6°C | 8.3°C | 102 mm | 70% | 3.1 m/s | 4.2 |
| 2011 | 22.4°C | 18.9°C | 15.4°C | 30.1°C | 9.2°C | 91 mm | 77% | 3.2 m/s | 3.8 |
| 2010 | 21.4°C | 17.6°C | 13.9°C | 29.9°C | 10.1°C | 83 mm | 73% | 3.8 m/s | 3.6 |
| 2009 | 22.0°C | 18.4°C | 14.9°C | 25.4°C | 7.7°C | 62 mm | 72% | 3 m/s | 4.4 |
| 2008 | 22.4°C | 18.6°C | 14.7°C | 28.7°C | 10.5°C | 77 mm | 75% | 2.9 m/s | 4 |
| 2007 | 23.7°C | 19.5°C | 15.3°C | 30.9°C | 9.7°C | 61 mm | 68% | 2.9 m/s | 4.5 |
| 2006 | 19.9°C | 16.7°C | 13.5°C | 25.7°C | 7.3°C | 122 mm | 79% | 3.5 m/s | 3.2 |
| 2005 | 24.0°C | 20.0°C | 15.9°C | 28.2°C | 10.3°C | 113 mm | 72% | 3.4 m/s | 4.7 |
| 2004 | 23.2°C | 19.5°C | 15.9°C | 28.2°C | 11.1°C | 86 mm | 74% | 3 m/s | 4.6 |
| 2003 | 20.2°C | 16.2°C | 12.3°C | 24.8°C | 6.4°C | 106 mm | 78% | 3.1 m/s | 4.1 |
| 2002 | 23.1°C | 18.4°C | 13.7°C | 31.1°C | 8.7°C | 86 mm | 71% | 2.8 m/s | 4.6 |
| 2001 | 19.9°C | 15.8°C | 11.7°C | 27.9°C | 6.2°C | 74 mm | 72% | 2.9 m/s | 4.3 |
| 2000 | 21.2°C | 17.4°C | 13.5°C | 29.9°C | 6.1°C | 107 mm | 73% | 3.6 m/s | 4 |
| 1999 | 22.6°C | 18.2°C | 13.8°C | 28.6°C | 6.1°C | 104 mm | 69% | 3 m/s | 4.2 |
| 1998 | 23.5°C | 19.5°C | 15.5°C | 29.0°C | 10.1°C | 45 mm | 68% | 3.2 m/s | 4.3 |
| 1997 | 21.3°C | 17.4°C | 13.4°C | 26.2°C | 7.9°C | 76 mm | 72% | 3.6 m/s | 3.9 |
| 1996 | 20.1°C | 16.3°C | 12.6°C | 27.2°C | 6.6°C | 93 mm | 78% | 3 m/s | 3.4 |
| 1995 | 19.4°C | 14.9°C | 10.4°C | 26.4°C | 5.4°C | 40 mm | 69% | 2.9 m/s | 4.1 |
| 1994 | 20.1°C | 15.7°C | 11.4°C | 25.0°C | 6.3°C | 49 mm | 74% | 2.9 m/s | 3.9 |
| 1993 ❄️ | 18.4°C | 14.5°C | 10.6°C | 26.5°C | 2.6°C | 71 mm | 74% | 3.3 m/s | 3.2 |
| 1992 | 19.1°C | 14.9°C | 10.7°C | 24.9°C | 4.4°C | 86 mm | 79% | 3.1 m/s | 4.1 |
| 1991 | 20.0°C | 15.6°C | 11.3°C | 26.8°C | 2.8°C | 46 mm | 66% | 2.9 m/s | 4.2 |
| 1990 | 19.4°C | 15.5°C | 11.5°C | 26.9°C | 4.5°C | 76 mm | 78% | 3.1 m/s | 3.6 |
| 1989 | 20.0°C | 15.8°C | 11.5°C | 25.8°C | 3.1°C | 81 mm | 75% | 2.8 m/s | 4 |
| 1988 | 19.9°C | 15.4°C | 11.0°C | 24.2°C | 6.4°C | 71 mm | 74% | 3.2 m/s | 4.3 |
| 1987 | 19.9°C | 15.9°C | 12.0°C | 25.2°C | 7.5°C | 92 mm | 80% | 2.5 m/s | 3.7 |
| 1986 🌧️ | 20.6°C | 16.7°C | 12.7°C | 25.6°C | 6.8°C | 140 mm | 77% | 3.2 m/s | 3.6 |
| 1985 | 22.4°C | 18.4°C | 14.4°C | 28.6°C | 9.0°C | 48 mm | 71% | 3.2 m/s | 4.5 |
| 1984 | 20.0°C | 16.1°C | 12.2°C | 25.5°C | 6.9°C | 105 mm | 72% | 3 m/s | 4 |
| 1983 | 22.4°C | 18.4°C | 14.4°C | 30.0°C | 7.9°C | 64 mm | 69% | 3.5 m/s | — |
| 1982 | 20.5°C | 16.5°C | 12.5°C | 28.6°C | 7.2°C | 105 mm | 75% | 2.7 m/s | — |
| 1981 | 19.3°C | 16.0°C | 12.8°C | 26.4°C | 6.1°C | 120 mm | 78% | 3.3 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 21.8°C with lows near 13.9°C (mean 17.9°C), based on 45 years of NASA POWER data.
September averages 78 mm of rainfall in St. Catharines, a relatively wet time of year. The wettest on record was 140 mm in 1986.
The hottest September reached 31.1°C in 2002. The coldest dipped to 2.6°C in 1993.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2.8°C. Daytime highs moved from 20.9°C to 23.8°C and overnight lows from 13.3°C to 16°C over the same span.
September is one of the warmer months of the year in St. Catharines and a relatively wet time of year, so plan for around 21.8°C daytime highs and 13.9°C at night.
Not quite — September is the 9th coolest month in St. Catharines, averaging 17.9°C.
For September in St. Catharines, pack light layers you can adjust through the day, with typical highs of 21.8°C and lows of 13.9°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 73% — moderately humid.
Average wind speed in September is 3.1 m/s. The windiest September on record averaged 3.8 m/s (2010).
The wettest September on record was 1986 with 140 mm. On average, September sees 78 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 St. Catharines 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.
