San Mateo Weather in September

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

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

September is in the fall / autumn in San Mateo and is typically the warmest month of the year. Daytime maximum temperatures average around a comfortable 24°C (75°F), whilst at night 13°C (56°F) is normal.

San Mateo weather averages (imperial / metric)
Daytime temperature 24.1°C 75.3°F
Nightly temperature 13.2°C 55.7°F
Average temperature 18.6°C 65.5°F
Daily sunshine 10.1 hrs
Avg rainfall 4 mm 0.2 ins
Rainy days 1 days
Sea temperature 14.4°C 57.9°F
Humidity 70%
Windspeed 16.2kph 10 mph

On average September is the 4th driest month of the year in San Mateo 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 10.1 hours of sunshine per day.

September temperatures in San Mateo

San Mateo average temperature in September

September rainfall

San Mateo average rain in September

September hourly sunshine

San Mateo 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 San Mateo 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

San Mateo weather stats

San Mateo weather statistics
Hottest month: September 23.8°C 74.8°F
Driest month: July 1mm 0ins
Sunniest month: April 11.1hrs
Coldest month: January 13.5°C 56.3°F
Wettest month: January 95mm 3.7ins
Map showing location of San Mateo (37.56299, -122.32553) San Mateo map pin © Google

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