Oswego Weather in September

The climate in Oswego during September can be summarized as warm, humid and wet.

September is in the fall / autumn in Oswego and is typically the 4th warmest month of the year. Daytime maximum temperatures average around a muggy 28°C (82°F), whilst at night 15°C (59°F) is normal.

On average September is the 3rd wettest month of the year in Oswego with around 121mm 4.8 inches of rain making it a wet 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 8.4 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 Oswego in September 2025.