Petersburg Weather in September

What's the weather like in Petersburg (Illinois) in September 2025?

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

September is in the fall / autumn in Petersburg and is typically the 4th warmest month of the year. Daytime maximum temperatures average around 26°C (78°F), whilst at night 13°C (55°F) is normal.

Petersburg weather averages (imperial / metric)
Daytime temperature 25.7°C 78.3°F
Nightly temperature 12.7°C 54.9°F
Average temperature 19.2°C 66.6°F
Daily sunshine 8.6 hrs
Avg rainfall 92 mm 3.6 ins
Rainy days 9 days
Sea temperature 19.6°C 67.3°F
Humidity 72%
Windspeed 14.4kph 9 mph

On average September is the 5th wettest month of the year in Petersburg with around 92mm 3.6 inches of rain making it a a little damp time to visit. This rainfall is typically spread over 9 days, although this may vary considerably.

On the flip side this corresponds to an average of 8.6 hours of sunshine per day.

September temperatures in Petersburg

Petersburg average temperature in September

September rainfall

Petersburg average rain in September

September hourly sunshine

Petersburg average rain in September

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 Petersburg in September 2025.

Other monthly averages

Best places to visit in September

UV index Best time to go?

Beta

Current (hourly) weather 15 day forecast

Petersburg weather stats

Petersburg weather statistics
Hottest month: July 30.2°C 86.4°F
Driest month: January 39mm 1.5ins
Sunniest month: July 10.9hrs
Coldest month: January -0.2°C 31.6°F
Wettest month: May 106mm 4.2ins
Map showing location of Petersburg (40.01172, -89.84817) Petersburg map pin © Google

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