Harrisburg Weather in September

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

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

September is in the fall / autumn in Harrisburg and is typically the 4th warmest month of the year. Daytime maximum temperatures average around a muggy 28°C (82°F), whilst at night 14°C (58°F) is normal.

Harrisburg weather averages (imperial / metric)
Daytime temperature 27.9°C 82.2°F
Nightly temperature 14.3°C 57.7°F
Average temperature 21.1°C 70°F
Daily sunshine 8.8 hrs
Avg rainfall 77 mm 3 ins
Rainy days 8 days
Sea temperature 22.5°C 72.4°F
Humidity 72%
Windspeed 11.9kph 7 mph

On average September is the 3rd driest month of the year in Harrisburg with around 77mm 3 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 8.8 hours of sunshine per day.

September temperatures in Harrisburg

Harrisburg average temperature in September

September rainfall

Harrisburg average rain in September

September hourly sunshine

Harrisburg 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 Harrisburg 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

Harrisburg weather stats

Harrisburg weather statistics
Hottest month: July 32.2°C 90°F
Driest month: October 74mm 2.9ins
Sunniest month: July 11hrs
Coldest month: January 4.7°C 40.5°F
Wettest month: May 129mm 5.1ins
Map showing location of Harrisburg (37.73838, -88.54061) Harrisburg map pin © Google

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