September is one of the warmer months of the year in Waterloo, with average highs near 22.5°C and lows around 10.5°C (mean 16.5°C). It is a relatively wet time of year, averaging 72 mm of rainfall and 72% relative humidity across the period.
September is one of the warmer months of the year in Waterloo. Across 45 years of records, the warmest September in Waterloo was 2002 — when the month averaged 19.6°C — while the coldest was 1993 at 13.4°C. Typical September days reach 22.5°C with nights near 10.5°C. The long-term trend is warming, about 0.7°C per decade.
September is a relatively wet time of year in Waterloo, averaging 72 mm of rainfall. The wettest September on record was 1986 with 182 mm, while the driest was 2023 at 20 mm.
Relative humidity in Waterloo during September averages 72%. The most humid September was 1981 at 79%, and the least humid was 2002 at 64%.
September receives about 4.1 kWh/m²/day of solar energy in Waterloo. The sunniest Septembers were 2004 and 2005 at 4.7 kWh/m²/day, and the cloudiest were 1993 and 2006 at 3.2.
Average wind speed in Waterloo during September is 2.8 m/s. The windiest September was 2010 at 3.4 m/s, while the calmest was 2025 at 2.1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 15.6°C | 15.5°C | 16.9°C | 17.2°C | 17.8°C | +2.2°C |
| Avg High | 21.4°C | 21.5°C | 23.0°C | 23.0°C | 23.9°C | +2.5°C |
| Avg Low | 9.7°C | 9.5°C | 10.8°C | 11.4°C | 11.6°C | +1.9°C |
| Avg Rain | 81 mm | 70 mm | 70 mm | 76 mm | 55 mm | -26 mm |
September temperatures in Waterloo have risen by about 2.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -1.9°C (1993) to a record high of 35.3°C (2002).
Rainfall in September is a relatively wet time of year, averaging 72 mm, with a wettest year of 182 mm.
One of the best times to visit Waterloo
September is one of the best times to visit Waterloo. Expect days averaging 22.5°C and nights around 10.5°C (mean 16.5°C) — warmer than Waterloo's yearly average — with moderate rainfall (72 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 | 24.9°C | 18.4°C | 11.9°C | 28.7°C | 6.1°C | 53 mm | 66% | 2.1 m/s | 4.6 |
| 2024 | 25.6°C | 19.3°C | 12.9°C | 29.7°C | 8.1°C | 32 mm | 68% | 2.4 m/s | 4.4 |
| 2023 | 24.1°C | 18.0°C | 12.0°C | 32.4°C | 7.1°C | 20 mm | 70% | 2.3 m/s | 4.2 |
| 2022 | 23.4°C | 17.4°C | 11.4°C | 32.2°C | 3.1°C | 34 mm | 70% | 2.5 m/s | 4 |
| 2021 | 22.7°C | 17.0°C | 11.2°C | 28.2°C | 5.1°C | 140 mm | 74% | 3.1 m/s | 4.3 |
| 2020 | 22.8°C | 16.6°C | 10.4°C | 29.6°C | 1.5°C | 52 mm | 72% | 3.1 m/s | 4.2 |
| 2019 | 23.8°C | 17.9°C | 11.9°C | 29.4°C | 7.5°C | 53 mm | 76% | 2.9 m/s | 3.8 |
| 2018 | 23.6°C | 18.3°C | 13.0°C | 32.2°C | 6.8°C | 62 mm | 76% | 2.8 m/s | 3.9 |
| 2017 | 24.4°C | 18.2°C | 11.9°C | 32.1°C | 4.3°C | 38 mm | 72% | 2.2 m/s | 4.6 |
| 2016 | 24.6°C | 18.7°C | 12.8°C | 32.2°C | 6.1°C | 64 mm | 70% | 2.7 m/s | 4.5 |
| 2015 | 25.0°C | 19.1°C | 13.2°C | 32.0°C | 6.4°C | 64 mm | 72% | 2.5 m/s | 4.3 |
| 2014 | 21.5°C | 15.9°C | 10.4°C | 30.2°C | 3.4°C | 119 mm | 77% | 2.5 m/s | 4.2 |
| 2013 | 21.6°C | 15.5°C | 9.4°C | 32.8°C | 2.8°C | 85 mm | 74% | 2.6 m/s | 4.2 |
| 2012 | 21.4°C | 15.7°C | 9.9°C | 31.2°C | 4.1°C | 96 mm | 71% | 2.6 m/s | 4.2 |
| 2011 | 22.3°C | 16.9°C | 11.5°C | 33.5°C | 5.0°C | 86 mm | 76% | 2.7 m/s | 3.7 |
| 2010 | 21.8°C | 16.0°C | 10.2°C | 32.9°C | 5.1°C | 87 mm | 73% | 3.4 m/s | 3.6 |
| 2009 | 22.7°C | 16.6°C | 10.6°C | 26.7°C | 3.1°C | 38 mm | 72% | 2.5 m/s | 4.4 |
| 2008 | 22.6°C | 16.7°C | 10.8°C | 31.5°C | 5.8°C | 96 mm | 76% | 2.3 m/s | 4.1 |
| 2007 | 25.1°C | 18.3°C | 11.5°C | 34.1°C | 4.1°C | 35 mm | 66% | 2.8 m/s | 4.5 |
| 2006 | 20.5°C | 15.2°C | 9.8°C | 27.2°C | 2.5°C | 78 mm | 76% | 3.1 m/s | 3.2 |
| 2005 | 25.0°C | 18.3°C | 11.7°C | 30.9°C | 5.4°C | 56 mm | 69% | 2.9 m/s | 4.7 |
| 2004 | 24.5°C | 18.0°C | 11.5°C | 29.4°C | 5.2°C | 36 mm | 70% | 2.6 m/s | 4.7 |
| 2003 | 21.7°C | 16.0°C | 10.3°C | 29.2°C | 3.1°C | 96 mm | 72% | 3.1 m/s | 4.2 |
| 2002 🔥 | 26.1°C | 19.6°C | 13.0°C | 35.3°C | 5.9°C | 61 mm | 64% | 2.7 m/s | 4.6 |
| 2001 | 21.5°C | 15.6°C | 9.8°C | 29.2°C | 2.1°C | 90 mm | 71% | 2.9 m/s | 4.2 |
| 2000 | 20.2°C | 14.6°C | 9.0°C | 29.9°C | -0.9°C | 118 mm | 78% | 2.9 m/s | 3.9 |
| 1999 | 23.7°C | 17.2°C | 10.6°C | 32.4°C | 1.4°C | 69 mm | 66% | 2.8 m/s | 4.4 |
| 1998 | 24.6°C | 18.1°C | 11.7°C | 30.7°C | 5.1°C | 39 mm | 66% | 2.8 m/s | 4.4 |
| 1997 | 21.6°C | 15.6°C | 9.7°C | 27.5°C | 1.9°C | 54 mm | 73% | 3 m/s | 4 |
| 1996 | 21.4°C | 16.1°C | 10.8°C | 29.9°C | 2.9°C | 119 mm | 75% | 2.7 m/s | 3.4 |
| 1995 | 20.9°C | 14.4°C | 7.9°C | 29.3°C | 2.5°C | 29 mm | 66% | 2.8 m/s | 4.3 |
| 1994 | 22.1°C | 15.8°C | 9.5°C | 29.4°C | 4.0°C | 43 mm | 73% | 2.8 m/s | 4 |
| 1993 ❄️ | 18.7°C | 13.4°C | 8.0°C | 28.3°C | -1.9°C | 92 mm | 74% | 3.1 m/s | 3.2 |
| 1992 | 19.8°C | 14.2°C | 8.7°C | 25.9°C | 0.6°C | 127 mm | 79% | 3.2 m/s | 3.8 |
| 1991 | 21.2°C | 15.0°C | 8.7°C | 30.5°C | -0.1°C | 44 mm | 66% | 2.8 m/s | 4.2 |
| 1990 | 21.3°C | 15.3°C | 9.3°C | 29.0°C | 1.6°C | 87 mm | 74% | 2.9 m/s | 3.8 |
| 1989 | 22.4°C | 16.2°C | 10.0°C | 29.2°C | -1.1°C | 54 mm | 69% | 2.8 m/s | 3.9 |
| 1988 | 22.0°C | 15.7°C | 9.4°C | 28.7°C | 5.5°C | 67 mm | 71% | 3.2 m/s | 4.1 |
| 1987 | 22.1°C | 16.4°C | 10.6°C | 29.1°C | 5.8°C | 43 mm | 74% | 2.6 m/s | 3.8 |
| 1986 🌧️ | 20.6°C | 14.9°C | 9.1°C | 26.1°C | 1.4°C | 182 mm | 79% | 2.8 m/s | 3.8 |
| 1985 | 22.5°C | 16.6°C | 10.6°C | 30.4°C | 2.5°C | 38 mm | 73% | 2.8 m/s | 4.2 |
| 1984 | 20.3°C | 14.4°C | 8.4°C | 27.5°C | 2.4°C | 80 mm | 73% | 2.7 m/s | 3.8 |
| 1983 | 23.3°C | 16.9°C | 10.4°C | 33.2°C | 3.6°C | 55 mm | 67% | 2.9 m/s | — |
| 1982 | 20.7°C | 15.0°C | 9.3°C | 29.7°C | 3.7°C | 94 mm | 77% | 2.5 m/s | — |
| 1981 | 18.9°C | 14.3°C | 9.7°C | 25.8°C | 1.2°C | 112 mm | 79% | 2.8 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 22.5°C with lows near 10.5°C (mean 16.5°C), based on 45 years of NASA POWER data.
September averages 72 mm of rainfall in Waterloo, a relatively wet time of year. The wettest on record was 182 mm in 1986.
The hottest September reached 35.3°C in 2002. The coldest dipped to -1.9°C in 1993.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2.6°C. Daytime highs moved from 21.1°C to 24.1°C and overnight lows from 9.7°C to 11.9°C over the same span.
September is one of the warmer months of the year in Waterloo and a relatively wet time of year, so plan for around 22.5°C daytime highs and 10.5°C at night.
Not quite — September is the 9th coolest month in Waterloo, averaging 16.5°C.
For September in Waterloo, pack light layers you can adjust through the day, with typical highs of 22.5°C and lows of 10.5°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 72% — moderately humid.
Average wind speed in September is 2.8 m/s. The windiest September on record averaged 3.4 m/s (2010).
The wettest September on record was 1986 with 182 mm. On average, September sees 72 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 Waterloo 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.
