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Seattle in September: weather, sea & travel advice
This month's data profile
Strong month under the current formula
Seattle in September is climatically well suited to city breaks and active holidays and hiking. The average daily high is around 21 °C, and the sea is about 11 °C. With about 9 rainy days it is moderate.
Historical monthly averages, not a weather forecast. Individual days and years can differ substantially.
Rank among 12 monthly averages
63/100 · #3
Warmth
#3
Dryness
#3
Sun
#6
Sea warmth
#3
Published best categories: Overall, City break, Active
Seattle · SeptemberPhoto: Daniel Schwen · CC BY-SA 4.0Climate facts
- Average high
- 21 °C
- Average low
- 11 °C
- Sea
- 11 °C
- Rainy days (est.)
- 9 rainy days (est.)
- Sun (est.)
- 5 h/day
- Humidity
- 78 %
Climate evidence with direct month comparison
The highlighted row is the selected month. Precipitation total and rainy days are separate monthly averages.
| Month | Avg high °C | Avg low °C | Rainy days (est.) | Precipitation mm | Sun h/day (est.) | Humidity % | Wind m/s | Sea °C | Score |
|---|---|---|---|---|---|---|---|---|---|
| August | 23 | 13 | 5 | 31 | 6.7 | 77 | 0.6 | 12 | 75 |
| September (selected) | 21 | 11 | 9 | 55 | 5.0 | 78 | 0.6 | 11 | 63 |
| October | 15 | 7 | 15 | 121 | 2.9 | 84 | 0.8 | 10 | 33 |
How do the previous and next months compare?
Baseline: September (63/100)
Positive and negative values show the change from the selected month.
| Score Δ | Average high Δ | Average low Δ | Rainy days Δ | Rain Δ | Sun Δ | Humidity Δ | Wind Δ | Sea Δ | |
|---|---|---|---|---|---|---|---|---|---|
| August | +12 | +2.7 °C | +2.3 °C | -3.6 | -24 mm | +1.7 h | -1.2 % | -0.1 m/s | +0.5 °C |
| October | -30 | -5.6 °C | -3.7 °C | +6.4 | +66.4 mm | -2.1 h | +5.9 % | +0.1 m/s | -1.2 °C |
All twelve months in context
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Useful next decisions
Frequently asked questions
How warm is Seattle in September?
The average daily high is around 21 °C, with an average daily low of about 11 °C.
Can you swim in Seattle in September?
The sea is about 11 °C (cold).
Does it rain a lot in Seattle in September?
The curated estimate is about 9 rainy days per month, not a directly measured long-term average. Total precipitation averages around 55 mm for the month. A rainy day does not mean all-day rain.
When is the best time to visit Seattle?
By the climate score, July, August and September are the strongest months for Seattle. For a beach trip: July and August. September is one of them.