Seattle weather in September
September in Seattle: nice, rainy, with clean air — an excellent time to visit.
#4 of 12 months in Seattle · #148 of 604 destinations to visit in September · comfort 87/100 (tier A)
Updated June 2026 · climate normals from ERA5 reanalysis
Seattle climate normals — September
| Daytime high | 22°C / 72°F | 😎 nice |
|---|---|---|
| Nighttime low | 13°C / 55°F | |
| Feels like (high) | 21°C / 70°F | |
| Rainfall | 86 mm / 3.4 in | 🌧 rainy |
| Rainy days | 10 days | |
| Humidity | 72% | 💧 humid |
| Dew point | 11°C / 52°F | |
| Sunshine | 9.5 h/day | |
| Daylight | 12.6 h | |
| Wind | 13 km/h / 8 mph | |
| Air quality (US AQI) | 40 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
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Seattle in September — FAQ
- Is September a good time to visit Seattle?
- September in Seattle: nice, rainy, with clean air — an excellent time to visit. It ranks #4 of 12 months for Seattle on SeasonMap's comfort score (87/100).
- What is the weather like in Seattle in September?
- In September, Seattle averages a daily high of 22°C and a low of 12.5°C, with about 86.1 mm of rain over roughly 10 rainy days.
- What is the air quality in Seattle in September?
- Seattle has a mean US Air Quality Index of about 40 in September.