Washington Weather in September

The climate in Washington during September can be summarized as warm, humid and reasonably dry.

September is in the fall / autumn in Washington and is typically the 4th warmest month of the year. Daytime maximum temperatures average around a muggy 29°C (84°F), whilst at night 16°C (62°F) is normal.

On average September is the 2nd driest month of the year in Washington with around 80mm 3.1 inches of rain making it a reasonably dry time to visit. This rainfall is typically spread over 8 days, although this may vary considerably.

On the flip side this corresponds to an average of 7.8 hours of sunshine per day.

The data used in these monthly averages covers a period of over 100 years right up until last year. As such they are a valid prediction of what to expect for the weather in Washington in September 2025.