September is one of the warmer months of the year in Olympia, with average highs near 20.8°C and lows around 9.9°C (mean 15.4°C). It is one of the drier months, averaging 67 mm of rainfall and 82% relative humidity across the period.
September is one of the warmer months of the year in Olympia. Across 45 years of records, the warmest Septembers in Olympia were 1990 and 2020 — when the month averaged 17.2°C — while the coldest was 1983 at 12.9°C. Typical September days reach 20.8°C with nights near 9.9°C. The long-term September temperature trend is broadly flat.
September is one of the drier months in Olympia, averaging 67 mm of rainfall. The wettest September on record was 2013 with 241 mm, while the driest was 1993 at 3 mm.
Relative humidity in Olympia during September averages 82%. The most humid September was 2010 at 90%, and the least humid was 1989 at 73%.
September receives about 4 kWh/m²/day of solar energy in Olympia. The sunniest September was 1998 at 4.8 kWh/m²/day, and the cloudiest were 2010, 2013 and 2019 at 3.2.
Average wind speed in Olympia during September is 0.3 m/s. The windiest Septembers were 2020, 2022 and 2023, among others at 0.3 m/s, while the calmest were 2021, 2024 and 2025, among others at 0.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 14.8°C | 15.8°C | 15.1°C | 15.4°C | 15.8°C | +1°C |
| Avg High | 20.6°C | 21.6°C | 20.6°C | 20.5°C | 21.0°C | +0.4°C |
| Avg Low | 9.1°C | 10.0°C | 9.7°C | 10.3°C | 10.6°C | +1.5°C |
| Avg Rain | 69 mm | 52 mm | 50 mm | 92 mm | 75 mm | +6 mm |
September temperatures in Olympia have risen by about 1.3°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 2.1°C (1983) to a record high of 35.6°C (2020).
Rainfall in September is one of the drier months, averaging 67 mm, with a wettest year of 241 mm.
Daytime highs and overnight lows have shifted differently — highs fell about 0.1°C per decade while lows rose 0.3°C per decade, narrowing the gap between day and night.
One of the best times to visit Olympia
September is one of the best times to visit Olympia. Expect days averaging 20.8°C and nights around 9.9°C (mean 15.4°C) — warmer than Olympia's yearly average — with moderate rainfall (67 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 | 19.6°C | 14.9°C | 10.1°C | 29.5°C | 7.6°C | 61 mm | 89% | 0.2 m/s | 4 |
| 2024 | 19.5°C | 14.9°C | 10.3°C | 33.6°C | 6.0°C | 53 mm | 87% | 0.2 m/s | 3.7 |
| 2023 | 20.8°C | 15.5°C | 10.2°C | 29.9°C | 5.4°C | 89 mm | 82% | 0.3 m/s | 3.9 |
| 2022 | 22.9°C | 17.0°C | 11.2°C | 32.9°C | 9.1°C | 11 mm | 79% | 0.3 m/s | 4.3 |
| 2021 | 20.6°C | 15.4°C | 10.1°C | 30.1°C | 7.5°C | 131 mm | 82% | 0.2 m/s | 3.8 |
| 2020 | 22.6°C | 17.2°C | 11.8°C | 35.6°C | 8.6°C | 107 mm | 82% | 0.3 m/s | 3.7 |
| 2019 | 19.2°C | 14.9°C | 10.5°C | 28.7°C | 2.4°C | 118 mm | 87% | 0.3 m/s | 3.2 |
| 2018 | 19.7°C | 14.5°C | 9.4°C | 29.1°C | 5.7°C | 78 mm | 83% | 0.3 m/s | 3.9 |
| 2017 | 21.9°C | 16.3°C | 10.7°C | 33.3°C | 7.6°C | 57 mm | 81% | 0.3 m/s | 3.8 |
| 2016 | 19.7°C | 14.6°C | 9.6°C | 24.7°C | 6.2°C | 68 mm | 82% | 0.2 m/s | 4 |
| 2015 | 19.6°C | 14.4°C | 9.2°C | 31.3°C | 4.3°C | 58 mm | 84% | 0.3 m/s | 3.8 |
| 2014 | 22.1°C | 16.5°C | 10.9°C | 31.5°C | 7.6°C | 80 mm | 81% | 0.3 m/s | 4.1 |
| 2013 🌧️ | 20.2°C | 15.8°C | 11.5°C | 30.7°C | 6.7°C | 241 mm | 89% | 0.2 m/s | 3.2 |
| 2012 | 21.5°C | 15.5°C | 9.5°C | 28.3°C | 6.2°C | 6 mm | 80% | 0.3 m/s | 4.6 |
| 2011 | 21.7°C | 16.2°C | 10.6°C | 28.7°C | 6.1°C | 77 mm | 83% | 0.3 m/s | 4 |
| 2010 | 19.6°C | 15.1°C | 10.6°C | 26.9°C | 7.3°C | 141 mm | 90% | 0.2 m/s | 3.2 |
| 2009 | 21.1°C | 15.6°C | 10.0°C | 32.6°C | 5.2°C | 68 mm | 80% | 0.3 m/s | 4.1 |
| 2008 | 21.1°C | 15.4°C | 9.7°C | 28.9°C | 6.3°C | 19 mm | 80% | 0.3 m/s | 4.2 |
| 2007 | 19.1°C | 14.3°C | 9.4°C | 28.8°C | 5.3°C | 67 mm | 84% | 0.2 m/s | 3.7 |
| 2006 | 22.4°C | 15.9°C | 9.5°C | 34.8°C | 6.6°C | 34 mm | 78% | 0.3 m/s | 4.4 |
| 2005 | 19.3°C | 14.0°C | 8.8°C | 24.1°C | 5.2°C | 53 mm | 82% | 0.3 m/s | 4.2 |
| 2004 | 19.1°C | 14.5°C | 10.0°C | 23.2°C | 7.5°C | 89 mm | 87% | 0.3 m/s | 3.6 |
| 2003 | 22.2°C | 16.2°C | 10.3°C | 31.8°C | 6.6°C | 44 mm | 80% | 0.2 m/s | 4.2 |
| 2002 | 20.9°C | 15.3°C | 9.6°C | 28.1°C | 6.8°C | 29 mm | 80% | 0.3 m/s | 4.3 |
| 2001 | 20.9°C | 15.3°C | 9.7°C | 26.5°C | 6.5°C | 28 mm | 82% | 0.3 m/s | 4 |
| 2000 | 19.8°C | 14.7°C | 9.5°C | 27.0°C | 3.8°C | 71 mm | 81% | 0.3 m/s | 3.9 |
| 1999 | 21.2°C | 14.9°C | 8.7°C | 30.9°C | 4.8°C | 11 mm | 79% | 0.3 m/s | 4.7 |
| 1998 | 22.4°C | 16.4°C | 10.4°C | 27.4°C | 7.5°C | 17 mm | 81% | 0.3 m/s | 4.8 |
| 1997 | 20.6°C | 16.0°C | 11.3°C | 28.4°C | 8.4°C | 188 mm | 87% | 0.3 m/s | 3.8 |
| 1996 | 18.8°C | 13.8°C | 8.8°C | 24.0°C | 5.3°C | 80 mm | 85% | 0.2 m/s | 3.6 |
| 1995 | 22.5°C | 16.8°C | 11.2°C | 30.5°C | 6.6°C | 86 mm | 82% | 0.3 m/s | 3.9 |
| 1994 | 22.4°C | 16.7°C | 11.0°C | 31.5°C | 7.8°C | 53 mm | 81% | 0.3 m/s | 4.1 |
| 1993 | 21.9°C | 15.7°C | 9.5°C | 30.8°C | 4.2°C | 3 mm | 78% | 0.3 m/s | 4.7 |
| 1992 | 19.8°C | 14.1°C | 8.3°C | 26.5°C | 4.7°C | 70 mm | 80% | 0.3 m/s | 4.1 |
| 1991 | 22.5°C | 16.4°C | 10.3°C | 29.7°C | 6.7°C | 4 mm | 79% | 0.3 m/s | 4.4 |
| 1990 🔥 | 23.6°C | 17.2°C | 10.9°C | 30.9°C | 7.5°C | 7 mm | 79% | 0.3 m/s | 4 |
| 1989 | 23.5°C | 16.6°C | 9.7°C | 31.8°C | 6.5°C | 9 mm | 73% | 0.3 m/s | 4.5 |
| 1988 | 20.6°C | 14.8°C | 9.0°C | 33.8°C | 5.0°C | 86 mm | 80% | 0.2 m/s | 4 |
| 1987 | 23.6°C | 16.9°C | 10.1°C | 30.5°C | 5.3°C | 23 mm | 75% | 0.3 m/s | 4.2 |
| 1986 | 19.1°C | 13.9°C | 8.7°C | 27.1°C | 6.5°C | 95 mm | 83% | 0.2 m/s | 3.5 |
| 1985 | 19.1°C | 13.7°C | 8.2°C | 24.2°C | 4.0°C | 85 mm | 79% | 0.3 m/s | 3.8 |
| 1984 | 18.8°C | 13.7°C | 8.5°C | 23.7°C | 4.8°C | 71 mm | 82% | 0.3 m/s | 3.7 |
| 1983 ❄️ | 18.3°C | 12.9°C | 7.6°C | 24.4°C | 2.1°C | 71 mm | 84% | 0.3 m/s | — |
| 1982 | 21.6°C | 15.9°C | 10.2°C | 30.3°C | 5.5°C | 73 mm | 80% | 0.3 m/s | — |
| 1981 | 20.4°C | 15.0°C | 9.6°C | 33.0°C | 6.9°C | 112 mm | 83% | 0.3 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 20.8°C with lows near 9.9°C (mean 15.4°C), based on 45 years of NASA POWER data.
September averages 67 mm of rainfall in Olympia, one of the drier months. The wettest on record was 241 mm in 2013.
The hottest September reached 35.6°C in 2020. The coldest dipped to 2.1°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.3°C. Daytime highs moved from 19.6°C to 20.7°C and overnight lows from 8.8°C to 10.4°C over the same span.
September is one of the warmer months of the year in Olympia and one of the drier months, so plan for around 20.8°C daytime highs and 9.9°C at night.
Not quite — September is the 10th coolest month in Olympia, averaging 15.4°C.
For September in Olympia, pack light layers you can adjust through the day, with typical highs of 20.8°C and lows of 9.9°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 82% — quite humid.
Average wind speed in September is 0.3 m/s. The windiest September on record averaged 0.3 m/s (1981).
The wettest September on record was 2013 with 241 mm. On average, September sees 67 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 Olympia 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.
