King County (Seattle)
September
Weather in King County for September 2025
Your guide to King County weather in September - trends and predictions
In general, the average temperature in King County at the beginning of September is 25.3 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 17 °F by the end of September.
King County sees moderate rainfall in September, averaging 7 rainy days.
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23
Dry days
7
Rainy days
0
Snow days
21°/10°
Temperatures
11 km/h
Avg max wind
71 %
Avg humidity
King County in September average weather
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| Mon. | Tue. | Wed. | Thu. | Fri. | Sat. | Sun. |
|---|---|---|---|---|---|---|
| 1  27° | 2  28° | 3  22° | 4  22° | 5 26° | 6  26° | 7  26° |
| 8 26° | 9 24° | 10 25° | 11 18° | 12 20° | 13 21° | 14 23° |
| 15 22° | 16 24° | 17 19° | 18 17° | 19 17° | 20 18° | 21 20° |
| 22 23° | 23  22° | 24 21° | 25  18° | 26 17° | 27  17° | 28 15° |
| 29 15° | 30 16° |
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Temperatures trend during September in King County
See the weather trend as well as the moving average line
September weather day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 | Mist | 27° /12° | 0 mm | 7 | |
| Sept. 2 | Sunny | 28° /13° | 0 mm | 7 | |
| Sept. 3 | Patchy rain possible | 22° /14° | 0.1 mm | 5 | |
| Sept. 4 | Overcast | 22° /11° | 0 mm | 5 | |
| Sept. 5 | Overcast | 26° /12° | 0 mm | 7 | |
| Sept. 6 | Cloudy | 26° /11° | 0 mm | 6 | |
| Sept. 7 | Partly cloudy | 26° /11° | 0 mm | 7 | |
| Sept. 8 | Partly cloudy | 26° /11° | 0 mm | 6 | |
| Sept. 9 | Mist | 24° /11° | 0 mm | 6 | |
| Sept. 10 | Overcast | 25° /11° | 0 mm | 6 | |
| Sept. 11 | Overcast | 18° /13° | 1.5 mm | 4 | |
| Sept. 12 | Overcast | 20° /11° | 0.1 mm | 5 | |
| Sept. 13 | Overcast | 21° /10° | 0.1 mm | 5 | |
| Sept. 14 | Mist | 23° /10° | 1.7 mm | 5 | |
| Sept. 15 | Mist | 22° /9° | 0 mm | 5 | |
| Sept. 16 | Overcast | 24° /8° | 0 mm | 6 | |
| Sept. 17 | Cloudy | 19° /11° | 0.8 mm | 5 | |
| Sept. 18 | Patchy rain possible | 17° /11° | 0.1 mm | 4 | |
| Sept. 19 | Overcast | 17° /11° | 0 mm | 4 | |
| Sept. 20 | Light rain shower | 18° /9° | 2.5 mm | 4 | |
| Sept. 21 | Partly cloudy | 20° /7° | 0 mm | 6 | |
| Sept. 22 | Sunny | 23° /9° | 0 mm | 6 | |
| Sept. 23 | Light rain | 22° /13° | 2.9 mm | 5 | |
| Sept. 24 | Light rain | 21° /10° | 4.9 mm | 5 | |
| Sept. 25 | Moderate or heavy rain with thunder | 18° /12° | 11.6 mm | 4 | |
| Sept. 26 | Moderate or heavy rain with thunder | 17° /10° | 14.2 mm | 4 | |
| Sept. 27 | Moderate rain | 17° /10° | 4.7 mm | 4 | |
| Sept. 28 | Light rain shower | 15° /9° | 4.7 mm | 4 | |
| Sept. 29 | Mist | 15° /7° | 0 mm | 4 | |
| Sept. 30 | Mist | 16° /6° | 0 mm | 4 | |
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Important Notice
Our weather forecast for King County in September is based on the analysis of historical data rather than real-time forecast models. While this provides a general overview, weather conditions can change. We recommend that you check the King County forecast closer to your planned date for the most up-to-date weather information.
King County in September - FAQ
What are the expected maximum and minimum temperatures in King County during September?
Enjoy moderate daytime temperatures of up to 21° and cooler nights around 10°. Ideal for a range of outdoor activities, from hiking to city tours.
How much rainfall should be expected in King County during September?
Moderate rainfall is anticipated in King County during September, with a total of 79.9 mm spread over approximately 7 days. Considering plans for rainy days is advisable.
What are the typical wind conditions in King County during September?
The average wind speed in King County during September is 11 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in King County
Explore the daily rainfall trends and prepare for King Countys September weather 💧
UV exposure in King County during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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Where is King County?Get accurate weather forecasts for King County, located at latitude 47.606 and longitude -122.332. Stay updated with localized weather information tailored for King County.
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