August is one of the warmer months of the year in Thunder Bay, with average highs near 23.1°C and lows around 12.2°C (mean 17.7°C). It is a relatively wet time of year, averaging 65 mm of rainfall and 74% relative humidity across the period.
August is one of the warmer months of the year in Thunder Bay. Across 45 years of records, the warmest August in Thunder Bay was 2021 — when the month averaged 20.3°C — while the coldest was 2004 at 14.6°C. Typical August days reach 23.1°C with nights near 12.2°C. The long-term trend is warming, about 0.4°C per decade.
August is a relatively wet time of year in Thunder Bay, averaging 65 mm of rainfall. The wettest August on record was 1988 with 164 mm, while the driest was 2007 at 18 mm.
Relative humidity in Thunder Bay during August averages 74%. The most humid August was 2009 at 80%, and the least humid was 2007 at 65%.
August receives about 5 kWh/m²/day of solar energy in Thunder Bay. The sunniest August was 2008 at 5.9 kWh/m²/day, and the cloudiest was 1988 at 4.1.
Average wind speed in Thunder Bay during August is 0.6 m/s. The windiest Augusts were 2023, 2024 and 2025, among others at 0.6 m/s, while the calmest were 2013, 2018 and 2022, among others at 0.5 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 16.9°C | 17.5°C | 17.4°C | 18.1°C | 18.7°C | +1.8°C |
| Avg High | 22.2°C | 23.1°C | 22.9°C | 23.5°C | 24.0°C | +1.8°C |
| Avg Low | 11.6°C | 11.8°C | 12.0°C | 12.7°C | 13.4°C | +1.8°C |
| Avg Rain | 92 mm | 56 mm | 64 mm | 56 mm | 51 mm | -41 mm |
August temperatures in Thunder Bay have risen by about 1.5°C between 1981–1985 and 2021–2025.
August has ranged from a record low of 3.8°C (1982) to a record high of 33.1°C (1983).
Rainfall in August is a relatively wet time of year, averaging 65 mm, with a wettest year of 164 mm.
One of the best times to visit Thunder Bay
August is one of the best times to visit Thunder Bay. Expect days averaging 23.1°C and nights around 12.2°C (mean 17.7°C) — warmer than Thunder Bay's yearly average — with moderate rainfall (65 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 | 23.6°C | 18.3°C | 13.0°C | 29.0°C | 7.0°C | 32 mm | 75% | 0.6 m/s | 4.9 |
| 2024 | 24.0°C | 18.8°C | 13.7°C | 30.5°C | 9.9°C | 55 mm | 74% | 0.6 m/s | 5 |
| 2023 | 23.0°C | 17.7°C | 12.4°C | 30.2°C | 7.4°C | 56 mm | 73% | 0.6 m/s | 4.7 |
| 2022 | 23.4°C | 18.2°C | 12.9°C | 27.6°C | 10.1°C | 49 mm | 76% | 0.5 m/s | 5.3 |
| 2021 🔥 | 26.0°C | 20.3°C | 14.7°C | 31.8°C | 10.2°C | 56 mm | 68% | 0.6 m/s | 4.7 |
| 2020 | 23.8°C | 18.6°C | 13.4°C | 29.7°C | 8.7°C | 61 mm | 75% | 0.6 m/s | 4.7 |
| 2019 | 22.9°C | 17.7°C | 12.4°C | 29.4°C | 8.7°C | 63 mm | 72% | 0.6 m/s | 5.1 |
| 2018 | 24.1°C | 18.2°C | 12.4°C | 31.1°C | 7.1°C | 57 mm | 75% | 0.5 m/s | 4.5 |
| 2017 | 21.5°C | 16.5°C | 11.5°C | 26.4°C | 6.2°C | 57 mm | 77% | 0.6 m/s | 4.7 |
| 2016 | 24.3°C | 19.2°C | 14.1°C | 29.7°C | 10.5°C | 61 mm | 75% | 0.6 m/s | 4.9 |
| 2015 | 22.4°C | 17.3°C | 12.2°C | 30.9°C | 8.3°C | 86 mm | 78% | 0.6 m/s | 4.4 |
| 2014 | 21.7°C | 16.4°C | 11.0°C | 27.4°C | 6.4°C | 50 mm | 79% | 0.6 m/s | 4.8 |
| 2013 | 23.9°C | 18.2°C | 12.6°C | 31.3°C | 7.7°C | 40 mm | 76% | 0.5 m/s | 5 |
| 2012 | 24.1°C | 18.7°C | 13.3°C | 30.9°C | 7.6°C | 42 mm | 69% | 0.6 m/s | 5.3 |
| 2011 | 24.6°C | 19.1°C | 13.7°C | 31.1°C | 10.1°C | 44 mm | 73% | 0.5 m/s | 5.4 |
| 2010 | 25.3°C | 19.7°C | 14.2°C | 31.4°C | 7.8°C | 67 mm | 72% | 0.6 m/s | 5.3 |
| 2009 | 20.7°C | 15.7°C | 10.8°C | 30.6°C | 5.7°C | 104 mm | 80% | 0.6 m/s | 4.7 |
| 2008 | 23.3°C | 17.7°C | 12.2°C | 27.9°C | 7.6°C | 57 mm | 75% | 0.6 m/s | 5.9 |
| 2007 | 24.0°C | 18.3°C | 12.6°C | 32.1°C | 7.1°C | 18 mm | 65% | 0.6 m/s | 5.2 |
| 2006 | 24.6°C | 18.9°C | 13.1°C | 29.8°C | 8.9°C | 25 mm | 66% | 0.6 m/s | 5.6 |
| 2005 | 23.5°C | 18.2°C | 12.9°C | 32.4°C | 7.8°C | 48 mm | 73% | 0.6 m/s | 5.1 |
| 2004 ❄️ | 19.9°C | 14.6°C | 9.2°C | 26.7°C | 4.8°C | 76 mm | 76% | 0.6 m/s | 4.7 |
| 2003 | 24.7°C | 18.8°C | 12.8°C | 30.7°C | 7.2°C | 58 mm | 74% | 0.5 m/s | 5.4 |
| 2002 | 22.2°C | 17.0°C | 11.7°C | 29.0°C | 8.3°C | 80 mm | 78% | 0.5 m/s | 4.9 |
| 2001 | 23.6°C | 18.4°C | 13.2°C | 30.8°C | 7.6°C | 85 mm | 78% | 0.5 m/s | 5.4 |
| 2000 | 22.0°C | 16.8°C | 11.7°C | 27.1°C | 8.0°C | 87 mm | 76% | 0.6 m/s | 4.7 |
| 1999 | 21.4°C | 16.5°C | 11.6°C | 28.1°C | 8.2°C | 108 mm | 77% | 0.6 m/s | 5.1 |
| 1998 | 24.9°C | 19.3°C | 13.8°C | 29.5°C | 7.8°C | 57 mm | 70% | 0.6 m/s | 5.1 |
| 1997 | 22.1°C | 16.6°C | 11.1°C | 28.3°C | 6.9°C | 23 mm | 72% | 0.5 m/s | 4.9 |
| 1996 | 23.3°C | 17.3°C | 11.3°C | 28.5°C | 7.4°C | 54 mm | 74% | 0.5 m/s | 5.5 |
| 1995 | 25.2°C | 19.0°C | 12.9°C | 29.8°C | 8.4°C | 46 mm | 66% | 0.5 m/s | 5.6 |
| 1994 | 21.8°C | 16.0°C | 10.2°C | 27.3°C | 5.9°C | 56 mm | 72% | 0.5 m/s | 4.6 |
| 1993 | 23.8°C | 18.2°C | 12.6°C | 30.9°C | 7.7°C | 57 mm | 75% | 0.5 m/s | 4.5 |
| 1992 | 21.1°C | 15.5°C | 9.9°C | 24.7°C | 6.2°C | 70 mm | 73% | 0.5 m/s | 4.5 |
| 1991 | 24.9°C | 19.0°C | 13.1°C | 31.9°C | 6.9°C | 22 mm | 68% | 0.5 m/s | 5.3 |
| 1990 | 22.7°C | 17.1°C | 11.4°C | 30.0°C | 6.2°C | 69 mm | 71% | 0.5 m/s | 5.1 |
| 1989 | 23.0°C | 17.1°C | 11.2°C | 31.0°C | 6.4°C | 71 mm | 73% | 0.5 m/s | 4.9 |
| 1988 🌧️ | 22.4°C | 17.5°C | 12.5°C | 29.6°C | 7.2°C | 164 mm | 79% | 0.5 m/s | 4.1 |
| 1987 | 21.3°C | 16.3°C | 11.3°C | 28.4°C | 5.5°C | 127 mm | 77% | 0.6 m/s | 4.5 |
| 1986 | 20.4°C | 15.3°C | 10.2°C | 27.3°C | 4.0°C | 56 mm | 76% | 0.6 m/s | 4.7 |
| 1985 | 19.9°C | 15.2°C | 10.4°C | 25.3°C | 7.1°C | 103 mm | 78% | 0.6 m/s | 4.5 |
| 1984 | 23.5°C | 18.1°C | 12.6°C | 31.2°C | 7.3°C | 67 mm | 77% | 0.5 m/s | 4.7 |
| 1983 | 25.7°C | 20.1°C | 14.4°C | 33.1°C | 11.0°C | 82 mm | 75% | 0.5 m/s | — |
| 1982 | 20.1°C | 14.8°C | 9.5°C | 26.5°C | 3.8°C | 91 mm | 76% | 0.5 m/s | — |
| 1981 | 23.2°C | 17.9°C | 12.5°C | 26.8°C | 7.9°C | 72 mm | 76% | 0.5 m/s | — |
Actual recorded August data for each year, 1981–2025 — sourced from NASA POWER.
The average high in August is around 23.1°C with lows near 12.2°C (mean 17.7°C), based on 45 years of NASA POWER data.
August averages 65 mm of rainfall in Thunder Bay, a relatively wet time of year. The wettest on record was 164 mm in 1988.
The hottest August reached 33.1°C in 1983. The coldest dipped to 3.8°C in 1982.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average August temperatures have risen by about 1.5°C. Daytime highs moved from 22.5°C to 24°C and overnight lows from 11.9°C to 13.3°C over the same span.
August is one of the warmer months of the year in Thunder Bay and a relatively wet time of year, so plan for around 23.1°C daytime highs and 12.2°C at night.
Not quite — August is the 12th coolest month in Thunder Bay, averaging 17.7°C.
For August in Thunder Bay, pack light layers you can adjust through the day, with typical highs of 23.1°C and lows of 12.2°C. Bring an umbrella or light rain jacket too.
Relative humidity in August averages 74% — moderately humid.
Average wind speed in August is 0.6 m/s. The windiest August on record averaged 0.6 m/s (1985).
The wettest August on record was 1988 with 164 mm. On average, August sees 65 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 Thunder Bay behaves each August, 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 August specifically, along with year-by-year records and how the month has changed over the decades.
