Weather in Tri-Cities, Washington for September 2025
Until now, September 2025 in Tri-Cities has been nearly identical to the historical average, with a temperature of 32.8 °F (showing only a slight deviation of 0.5 °F).
The forecast for the next days in Tri-Cities predicts a temperature of 25.9 °F, which is cooler than the historical average.
In general, the average temperature in Tri-Cities at the beginning of September is 34.4 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 19.4 °F by the end of September.
With an average of 4 rainy days, Tri-Cities experiences minimal rainfall in September.
New! Chat with our AI weatherman - it’s amazing and free.
Temperatures
Rain 🌧️
More
Tri-Cities Weather September
Temperatures trend during September in Tri-Cities
September weather in Tri-Cities day by day
| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Light rain | 35° /17° | 2.5 mm | 8 | |
| Sept. 2 |  Patchy rain possible | 36° /17° | 0.2 mm | 8 | |
| Sept. 3 |  Sunny | 34° /18° | 0.1 mm | 8 | |
| Sept. 4 |  Overcast | 34° /16° | 0 mm | 7 | |
| Sept. 5 | Sunny | 34° /17° | 0 mm | 8 | |
| Sept. 6 | Sunny | 34° /17° | 0 mm | 8 | |
| Sept. 7 | Sunny | 34° /17° | 0 mm | 8 | |
| Sept. 8 |  Partly cloudy | 33° /17° | 0 mm | 8 | |
| Sept. 9 | Sunny | 30° /16° | 0 mm | 7 | |
| Sept. 10 | Partly cloudy | 32° /15° | 0 mm | 7 | |
| Sept. 11 | Overcast | 26° /16° | 2.7 mm | 6 | |
| Sept. 12 | Overcast | 28° /13° | 0 mm | 6 | |
| Sept. 13 | Sunny | 29° /13° | 0 mm | 7 | |
| Sept. 14 | Sunny | 26° /13° | 1.5 mm | 7 | |
| Sept. 15 | Sunny | 27° /9° | 0 mm | 1.1 | |
| Sept. 16 | Sunny | 30° /9° | 0 mm | 1.4 | |
| Sept. 17 | Sunny | 33° /14° | 0 mm | 1.4 | |
| Sept. 18 | Partly cloudy | 34° /18° | 0 mm | 1.3 | |
| Sept. 19 | Partly cloudy | 34° /20° | 0 mm | 0 | |
| Sept. 20 | Partly cloudy | 28° /17° | 0 mm | 6 | |
| Sept. 21 | Partly cloudy | 28° /17° | 0 mm | 6 | |
| Sept. 22 | Sunny | 27° /14° | 0 mm | 6 | |
| Sept. 23 | Partly cloudy | 27° /17° | 0 mm | 6 | |
| Sept. 24 | Patchy rain possible | 19° /13° | 0.1 mm | 4 | |
| Sept. 25 | Partly cloudy | 22° /11° | 0 mm | 5 | |
| Sept. 26 | Patchy rain possible | 17° /9° | 2.5 mm | 3 | |
| Sept. 27 | Patchy rain possible | 17° /8° | 0.3 mm | 3 | |
| Sept. 28 | Sunny | 20° /9° | 0 mm | 4 | |
| Sept. 29 | Light drizzle | 20° /9° | 0.4 mm | 5 | |
| Sept. 30 | Patchy rain possible | 21° /5° | 1.7 mm | 5 | |
| Next | |||||
Tri-Cities in September - FAQ
September rainfall patterns in Tri-Cities
UV exposure in Tri-Cities during September
Quick links
Where is Tri-Cities?Get accurate weather forecasts for Tri-Cities, located at latitude 46.245 and longitude -119.196. Stay updated with localized weather information tailored for Tri-Cities.