Washington weather in September
September in Washington: warm, rainy, with clean air — an excellent time to visit.
#3 of 12 months in Washington · #210 of 604 destinations to visit in September · comfort 85/100 (tier A)
Updated June 2026 · climate normals from ERA5 reanalysis
Washington climate normals — September
| Daytime high | 27°C / 80°F | 🌤 warm |
|---|---|---|
| Nighttime low | 18°C / 64°F | |
| Feels like (high) | 28°C / 82°F | |
| Rainfall | 80 mm / 3.1 in | 🌧 rainy |
| Rainy days | 9 days | |
| Humidity | 69% | 💧 humid |
| Dew point | 15°C / 59°F | |
| Sunshine | 9.2 h/day | |
| Daylight | 12.4 h | |
| Wind | 13 km/h / 8 mph | |
| Air quality (US AQI) | 47 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
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Washington in September — FAQ
- Is September a good time to visit Washington?
- September in Washington: warm, rainy, with clean air — an excellent time to visit. It ranks #3 of 12 months for Washington on SeasonMap's comfort score (85/100).
- What is the weather like in Washington in September?
- In September, Washington averages a daily high of 26.7°C and a low of 17.7°C, with about 80 mm of rain over roughly 9 rainy days.
- What is the air quality in Washington in September?
- Washington has a mean US Air Quality Index of about 47 in September.