Cos Cob Weather in September

What's the weather like in Cos Cob (Connecticut) in September 2025?

The climate in Cos Cob during September can be summarized as mild and damp.

September is in the fall / autumn in Cos Cob and is typically the 4th warmest month of the year. Daytime maximum temperatures average around 24°C (74°F), whilst at night 12°C (53°F) is normal.

Cos Cob weather averages (imperial / metric)
Daytime temperature 23.6°C 74.4°F
Nightly temperature 11.5°C 52.6°F
Average temperature 17.5°C 63.5°F
Daily sunshine 7.8 hrs
Avg rainfall 100 mm 3.9 ins
Rainy days 8 days
Sea temperature 20°C 68°F
Humidity 72%
Windspeed 16.6kph 10 mph

On average September is the 6th driest month of the year in Cos Cob with around 100mm 3.9 inches of rain making it a damp 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 7.8 hours of sunshine per day.

September temperatures in Cos Cob

Cos Cob average temperature in September

September rainfall

Cos Cob average rain in September

September hourly sunshine

Cos Cob 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 Cos Cob 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

Cos Cob weather stats

Cos Cob weather statistics
Hottest month: July 28.4°C 83.1°F
Driest month: February 90mm 3.5ins
Sunniest month: August 9.1hrs
Coldest month: January 2.3°C 36.1°F
Wettest month: May 126mm 5ins
Map showing location of Cos Cob (41.03343, -73.59957) Cos Cob map pin © Google

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