Washington Weather in September

The climate in Washington during September can be summarized as warm and a little damp.

September is in the fall / autumn in Washington and is typically the 4th warmest month of the year. Daytime maximum temperatures average around a comfortable 26°C (79°F), whilst at night 13°C (55°F) is normal.

On average September is the 5th wettest month of the year in Washington with around 93mm 3.6 inches of rain making it a a little damp 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 8.9 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.