Stony Brook Weather in September

What's the weather like in Stony Brook (New York) in September 2025?

The climate in Stony Brook during September can be summarized as warm and a little damp.

September is in the fall / autumn in Stony Brook and is typically the 4th warmest month of the year. Daytime maximum temperatures average around 24°C (74°F), whilst at night 14°C (57°F) is normal.

Stony Brook weather averages (imperial / metric)
Daytime temperature 23.5°C 74.3°F
Nightly temperature 14.1°C 57.4°F
Average temperature 18.8°C 65.8°F
Daily sunshine 8 hrs
Avg rainfall 89 mm 3.5 ins
Rainy days 8 days
Sea temperature 20.6°C 69.1°F
Humidity 75%
Windspeed 16.6kph 10 mph

On average September is the 4th driest month of the year in Stony Brook with around 89mm 3.5 inches of rain making it a a little 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 8 hours of sunshine per day.

September temperatures in Stony Brook

Stony Brook average temperature in September

September rainfall

Stony Brook average rain in September

September hourly sunshine

Stony Brook 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 Stony Brook 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

Stony Brook weather stats

Stony Brook weather statistics
Hottest month: July 27.6°C 81.7°F
Driest month: February 84mm 3.3ins
Sunniest month: August 9.1hrs
Coldest month: January 2.9°C 37.2°F
Wettest month: November 107mm 4.2ins
Map showing location of Stony Brook (40.92565, -73.14094) Stony Brook map pin © Google

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