Guerneville Weather in September

What's the weather like in Guerneville (California) in September 2025?

The climate in Guerneville during September can be summarized as warm and dry.

September is in the fall / autumn in Guerneville and is typically the 3rd warmest month of the year. Daytime maximum temperatures average around a comfortable 28°C (83°F), whilst at night 11°C (51°F) is normal.

Guerneville weather averages (imperial / metric)
Daytime temperature 28.4°C 83°F
Nightly temperature 10.7°C 51.2°F
Average temperature 19.5°C 67.1°F
Daily sunshine 10.1 hrs
Avg rainfall 14 mm 0.5 ins
Rainy days 2 days
Sea temperature 14.4°C 57.9°F
Humidity 68%
Windspeed 14.8kph 9 mph

On average September is the 4th driest month of the year in Guerneville with around 14mm 0.5 inches of rain making it a dry time to visit. This rainfall is typically spread over 2 days, although this may vary considerably.

On the flip side this corresponds to an average of 10.1 hours of sunshine per day.

September temperatures in Guerneville

Guerneville average temperature in September

September rainfall

Guerneville average rain in September

September hourly sunshine

Guerneville 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 Guerneville 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

Guerneville weather stats

Guerneville weather statistics
Hottest month: July 29.3°C 84.7°F
Driest month: July 2mm 0.1ins
Sunniest month: April 10.9hrs
Coldest month: January 13.3°C 55.9°F
Wettest month: January 234mm 9.2ins
Map showing location of Guerneville (38.50186, -122.99611) Guerneville map pin © Google

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