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 25.9 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 18.9 °F by the end of September.
The climate of King County in September is notably wet, with an average of 14 rainy days, and a total of 55.2 mm of precipitation.
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Temperatures
Rain 🌧️
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16
Dry days
14
Rainy days
0
Snow days
22°/11°
Temperatures
11 km/h
Avg max wind
69 %
Avg humidity
King County in September average weather
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| Mon. | Tue. | Wed. | Thu. | Fri. | Sat. | Sun. |
|---|---|---|---|---|---|---|
| 1  26° | 2  28° | 3  24° | 4 24° | 5 26° | 6 26° | 7 27° |
| 8 26° | 9  25° | 10  27° | 11  21° | 12 22° | 13 21° | 14 22° |
| 15 21° | 16 21° | 17 18° | 18 18° | 19 18° | 20 20° | 21 22° |
| 22 21° | 23 21° | 24 22° | 25 21° | 26 19° | 27  20° | 28 16° |
| 29 17° | 30 17° |
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Temperatures trend during September in King County
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September weather day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 | Partly cloudy | 26° /11° | 0 mm | 7 | |
| Sept. 2 | Sunny | 28° /12° | 0 mm | 7 | |
| Sept. 3 | Overcast | 24° /13° | 0.1 mm | 6 | |
| Sept. 4 | Partly cloudy | 24° /11° | 0.2 mm | 6 | |
| Sept. 5 | Overcast | 26° /13° | 0.4 mm | 6 | |
| Sept. 6 | Sunny | 26° /11° | 0.7 mm | 6 | |
| Sept. 7 | Partly cloudy | 27° /11° | 0 mm | 7 | |
| Sept. 8 | Partly cloudy | 26° /12° | 0.2 mm | 6 | |
| Sept. 9 | Cloudy | 25° /11° | 0 mm | 6 | |
| Sept. 10 | Patchy rain possible | 27° /11° | 0.1 mm | 6 | |
| Sept. 11 | Moderate rain at times | 21° /13° | 1.1 mm | 5 | |
| Sept. 12 | Patchy rain possible | 22° /11° | 0.7 mm | 5 | |
| Sept. 13 | Partly cloudy | 21° /11° | 0.2 mm | 5 | |
| Sept. 14 | Patchy rain possible | 22° /10° | 1.6 mm | 5 | |
| Sept. 15 | Patchy rain possible | 21° /9° | 1.4 mm | 5 | |
| Sept. 16 | Overcast | 21° /9° | 0.7 mm | 5 | |
| Sept. 17 | Overcast | 18° /10° | 6.3 mm | 4 | |
| Sept. 18 | Patchy rain possible | 18° /10° | 2.8 mm | 4 | |
| Sept. 19 | Moderate or heavy rain shower | 18° /10° | 3.7 mm | 5 | |
| Sept. 20 | Cloudy | 20° /9° | 1.2 mm | 5 | |
| Sept. 21 | Partly cloudy | 22° /7° | 0 mm | 6 | |
| Sept. 22 | Overcast | 21° /10° | 0 mm | 5 | |
| Sept. 23 | Overcast | 21° /12° | 1.5 mm | 5 | |
| Sept. 24 | Sunny | 22° /10° | 2.4 mm | 5 | |
| Sept. 25 | Sunny | 21° /11° | 5.8 mm | 5 | |
| Sept. 26 | Moderate rain at times | 19° /11° | 9.2 mm | 5 | |
| Sept. 27 | Heavy rain at times | 20° /10° | 4.7 mm | 5 | |
| Sept. 28 | Heavy rain at times | 16° /10° | 5.2 mm | 4 | |
| Sept. 29 | Moderate rain at times | 17° /9° | 0.8 mm | 4 | |
| Sept. 30 | Moderate or heavy rain shower | 17° /7° | 4.5 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 22° and cooler nights around 11°. 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 55.2 mm spread over approximately 14 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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