Sunnyvale Weather in September

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

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

September is in the fall / autumn in Sunnyvale and is typically the 3rd warmest month of the year. Daytime maximum temperatures average around a comfortable 26°C (78°F), whilst at night 13°C (55°F) is normal.

Sunnyvale weather averages (imperial / metric)
Daytime temperature 25.8°C 78.4°F
Nightly temperature 12.6°C 54.7°F
Average temperature 19.2°C 66.6°F
Daily sunshine 10.3 hrs
Avg rainfall 4 mm 0.2 ins
Rainy days 1 days
Sea temperature 14.4°C 57.9°F
Humidity 68%
Windspeed 15.8kph 10 mph

On average September is the 4th driest month of the year in Sunnyvale with around 4mm 0.2 inches of rain making it a very dry time to visit.

On the flip side this corresponds to an average of 10.3 hours of sunshine per day.

September temperatures in Sunnyvale

Sunnyvale average temperature in September

September rainfall

Sunnyvale average rain in September

September hourly sunshine

Sunnyvale 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 Sunnyvale 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

Sunnyvale weather stats

Sunnyvale weather statistics
Hottest month: August 25.6°C 78.1°F
Driest month: July 1mm 0ins
Sunniest month: April 11.2hrs
Coldest month: January 13.9°C 57°F
Wettest month: January 87mm 3.4ins
Map showing location of Sunnyvale (37.36883, -122.03635) Sunnyvale map pin © Google

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