Seattle weather in September
Temperature, sea and sunshine in September: long-term averages from 30 years of weather data, not a forecast.
Holiday weather in September
Excellent
Best time to visit: July – September
What is the weather like in Seattle in September?
In September, Seattle is mild: daytime highs average 21 °C, and nights cool down to about 11 °C. The sea averages 11.3 °C – swimming is only for the hardy. The sun shines for around 7 hours a day. Rain falls on about 9 days, adding up to 72 mm. All in all, September is an excellent month for a holiday in Seattle.
September compared
How the weather changes from August to October. Tap a month to open it.
| AugustAug | SeptemberSep | OctoberOct | |
|---|---|---|---|
| Score | 96 | 82 | 44 |
| Day | 24° | 21° | 15° |
| Night | 14° | 11° | 7° |
| Sea | 12° | 11° | 10° |
| Sun | 9 h | 7 h | 4 h |
| Rain days | 5 | 9 | 15 |
More details for September
- Daylight
- 12 h 39 min06:45 – 19:24
- UV index
- 5 · moderateclear sky, noon (estimate)All months
- Muggy days
- 0 daysdew point 18 °C or moreAll months
- Wind
- 13 km/haverage daily peakAll months
- Cloud cover
- 50 %on averageAll months
- Hot days
- 0 days30 °C or moreAll months
- Snow days
- 0 days1 cm or more of fresh snowAll months
- Time zone
- UTC−7America/Los_Angeles
How the score comes together
- Temperatureweight 50 %100 %
- Sunshineweight 20 %63 %
- Few rainy daysweight 30 %66 %
Each factor is rated from 0 to 100 % and weighted for the travel style “City break”.
What to pack in September
- Sunscreen
- A jumper for the evenings
- Rain jacket or umbrella
Seattle in September: quick answers
Is Seattle hot in September?
No. In September, Seattle is mild: daytime highs average 21 °C and nights drop to about 11 °C.
Can you swim in Seattle in September?
Only if you don't mind cold water: in September the sea averages just 11.3 °C. Comfortable swimming temperatures are not reached at any time of year.
Does it rain much in Seattle in September?
Rain falls on about 9 days, adding up to 72 mm.
Seattle month by month
The whole year in SeattleAll destinations: USAWhere to go in SeptemberSea temperature in September
Climate averages 1996–2025, not a forecast. Data: Copernicus ERA5 / ERA5-Land via Open-Meteo.com (CC BY 4.0), NOAA OISST, WMO 1991–2020 (NOAA NCEI), GeoNames (CC BY 4.0). Sources & licences