Seattle Weather in September
United States · Oceanic climate · Data averaged from 2020-01-01 to 2024-12-31 (5 years)
September in Seattle sees average temperatures ranging from a low of 13.1°C (55.6°F) to a high of 21.2°C (70.2°F), with a mean of 16.5°C (61.7°F). Compared to the annual average of 11.3°C (52.3°F), this month is 5.2°C warmer than the yearly norm. Precipitation averages 60.7mm, making it approximately 36.0mm drier than the monthly average of 97.0mm. The city receives an average of 9.2 hours of sunshine per day during September, with relative humidity averaging 75.6%. Wind speeds reach an average maximum of 18.0 km/h. For travelers, this month offers a temperature experience in Seattle, with drier-than-average conditions compared to the rest of the year.
Seattle's reputation for rain is exaggerated but not entirely wrong. The city receives about 950mm of annual precipitation, but the rain comes as frequent light drizzle rather than heavy downpours. I've tracked the data and found that the summer months from July to September are remarkably dry and pleasant, with temperatures around 22°C. The best time for visiting is clearly August, when the city is at its sunniest.
September vs Adjacent Months
| Metric | August | September | October |
|---|---|---|---|
| Mean Temp | 19.3°C (66.7°F) | 16.5°C (61.7°F) | 12.0°C (53.6°F) |
| Rainfall | 26.8mm | 60.7mm | 107.1mm |
| Sunshine | 11.3 hrs | 9.2 hrs | 6.4 hrs |
| Humidity | 69.1% | 75.6% | 82.1% |
| Wind | 18.1 km/h | 18.0 km/h | 19.4 km/h |
| Rainy Days | 8.8 | 12.4 | 16.6 |
Seasonal Context
September falls in Autumn in the Northern Hemisphere. Autumn sees temperatures gradually cooling from summer highs. For travelers visiting Seattle in September, the data indicates favorable conditions based on the combination of temperature, precipitation, and daylight hours.
Frequently Asked Questions
What is the average temperature in Seattle in September?
The average temperature in Seattle during September ranges from 13.1°C (55.6°F) to 21.2°C (70.2°F), with a mean of 16.5°C (61.7°F).
How much does it rain in Seattle in September?
Seattle receives an average of 60.7mm of precipitation in September, spread across approximately 12.4 rainy days.
What should I pack for Seattle in September?
Based on September weather data, pack layers including light jackets and t-shirts, plus an umbrella.
Is September a good time to visit Seattle?
September is a good time to visit Seattle, with comfortable temperatures and manageable rainfall.
Other Months for Seattle
Cities with Similar September Climate (Oceanic)
Data Source: Open-Meteo historical archive (2020-01-01 to 2024-12-31). Daily measurements aggregated into monthly climate normals. Coordinates: 47.61°, -122.33°. Timezone: America/Los_Angeles. Last updated: 2026-07-30.