Altadena Weather in September

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

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

September is in the fall / autumn in Altadena and is typically the 3rd warmest month of the year. Daytime maximum temperatures average around a comfortable 28°C (82°F), whilst at night 12°C (54°F) is normal.

Altadena weather averages (imperial / metric)
Daytime temperature 27.9°C 82.2°F
Nightly temperature 12.1°C 53.8°F
Average temperature 20°C 68°F
Daily sunshine 10.2 hrs
Avg rainfall 8 mm 0.3 ins
Rainy days 2 days
Sea temperature 18.6°C 65.5°F
Humidity 63%
Windspeed 12.6kph 8 mph

On average September is the 4th driest month of the year in Altadena with around 8mm 0.3 inches of rain making it a very dry time to visit.

On the flip side this corresponds to an average of 10.2 hours of sunshine per day.

September temperatures in Altadena

Altadena average temperature in September

September rainfall

Altadena average rain in September

September hourly sunshine

Altadena 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 Altadena 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

Altadena weather stats

Altadena weather statistics
Hottest month: July 31°C 87.8°F
Driest month: June 3mm 0.1ins
Sunniest month: August 11.6hrs
Coldest month: December 12.7°C 54.9°F
Wettest month: January 76mm 3ins
Map showing location of Altadena (34.18973, -118.13118) Altadena map pin © Google

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