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September Weather in Cos Cob, United States

Last updated: June 24, 2025

In September, the average temperature in Cos Cob, United States hovers around 21°C (69°F), offering a pleasant climate ideal for outdoor activities. Expect a minimum of 9°C (48°F) and a maximum of 32°C (90°F), making it a season of diverse weather experiences. With approximately 93 mm (3.6 in) of precipitation spread over 9 days, it's wise to keep an umbrella handy. The average humidity rests at a comfortable 68%, adding to the region's inviting atmosphere.

September Temperature in Cos Cob

In September in Cos Cob, the average temperature is 21°C (69°F), with maximums reaching up to 32°C (90°F) and minimums dropping as low as 9°C (48°F). This makes it an ideal time for travelers to enjoy a variety of outdoor activities while packing for both warm days and cooler evenings.

September Weather in Cos Cob: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Cos Cob, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Cos Cob, September typically has an average temperature of 21°C (69°F), with highs reaching up to 32°C (90°F) and lows dropping to around 9°C (48°F).
JanFebMarAprMayJunJulAugSepOctNovDec333540506070777569604638
Data source: Temperature data for Cos Cob generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Cos Cob

In Cos Cob in September, the precipitation amount is 93 mm (3.6 in) during a span of 9 days.

September Precipitation Trends in Cos Cob

The chart displays monthly precipitation patterns in Cos Cob, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Cos Cob, September typically receives around 93 mm (3.6 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec6910193116112941391189313190114
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Cos Cob

In Cos Cob in September humidity is 68%. With average temperature 21°C (69°F), this humidity feels like a warm embrace, making it essential for travelers to stay hydrated and take breaks in the shade while exploring the local sights.

September Average Humidity in Cos Cob

This chart illustrates the average monthly humidity levels in Cos Cob, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Cos Cob is approximately 68%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec84%82%81%78%70%69%62%65%68%74%82%80%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Cos Cob

In Cos Cob in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Cos Cob.

Maximum UV Index Levels in Cos Cob for September

The chart shows the monthly maximum UV Index (UVI) for Cos Cob in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Cos Cob typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec35681010998642
Data source: Cos Cob September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How September Weather in Cos Cob Compares to Other Months

Weather in Cos Cob varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Cos Cob, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Cos Cob, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather1°C (34°F)69 mm (2.7 inches)84%moderate
February Weather2°C (36°F)101 mm (4.0 inches)82%moderate
March Weather5°C (41°F)93 mm (3.7 inches)81%high
April Weather10°C (50°F)116 mm (4.6 inches)78%very high
May Weather15°C (60°F)112 mm (4.4 inches)69%very high
June Weather21°C (70°F)93 mm (3.7 inches)69%very high
July Weather25°C (77°F)139 mm (5.5 inches)62%very high
August Weather24°C (75°F)118 mm (4.6 inches)65%very high
September Weather21°C (69°F)93 mm (3.6 inches)68%very high
October Weather15°C (60°F)131 mm (5.2 inches)74%high
November Weather8°C (47°F)90 mm (3.6 inches)82%moderate
December Weather3°C (39°F)113 mm (4.5 inches)80%low

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