Month by month
| Month | Afternoon | Sea | Rain | Verdict |
|---|---|---|---|---|
| January | 8.1 °C | 8.3 °C | 18 days | Unfavourable season |
| February | 8.3 °C | 8.3 °C | 15 days | Unfavourable season |
| March | 11 °C | 8.4 °C | 15 days | Unfavourable season |
| April | 13.8 °C | 9.1 °C | 14 days | Possible, with trade-offs |
| May | 17.9 °C | 10 °C | 10 days | Possible, with trade-offs |
| June | 21.1 °C | 10.6 °C | 8 days | Pleasant — a good time to go |
| July | 24.6 °C | 11.2 °C | 4 days | Ideal — one of the best times of year |
| August | 24.8 °C | 11.7 °C | 5 days | Ideal — one of the best times of year |
| September | 20.5 °C | 11.3 °C | 10 days | Pleasant — a good time to go |
| October | 15.1 °C | 10.3 °C | 14 days | Possible, with trade-offs |
| November | 10.3 °C | 9.7 °C | 18 days | Unfavourable season |
| December | 7.4 °C | 8.8 °C | 19 days | Unfavourable season |
Before you go
Three things to check once you have picked your dates.
Entry
Entry rules depend on your nationality and change often. Check them before booking.
Safety
No specific restrictions
Usual precautions apply.
Official advice updated 18 August 2026
Health
Recommended vaccinations, water quality, mosquitoes: advice depends on the country and the season. Some vaccines need time before departure.
Beau Fixe is not a safety or health authority. These notes summarise public advisories and link to their source; only the competent authorities are authoritative. Alert levels: Foreign, Commonwealth & Development Office (gov.uk), Open Government Licence v3.0.
FAQ
Can you swim in Seattle in September?
The sea averages 11.3°C in September — too cold for most swimmers.
How hot is Seattle in September?
Expect 20.5°C in the afternoon and 12.7°C at night, averaged over the last 10 years.
Does it rain a lot in Seattle in September?
Around 10 days with rain (≥ 1 mm) in the month — 35% of days.