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September Weather in Groton, United States

Last updated: June 24, 2025

In Groton, United States, the average temperature in September hovers around 17°C (62°F). However, temperatures can fluctuate significantly, with minimums dipping to -1°C (31°F) and maximums soaring up to 32°C (90°F). During this month, expect about 99 mm (3.9 in) of precipitation over 10 days, contributing to an average humidity level of 78%. Prepare for a season of diverse weather!

September Temperature in Groton

In September in Groton, the average temperature is 17°C (62°F), with maximums reaching up to 32°C (90°F) and minimums dropping as low as -1°C (31°F). Be sure to pack for a range of temperatures to enjoy your travels comfortably.

September Weather in Groton: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Groton, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Groton, September typically has an average temperature of 17°C (62°F), with highs reaching up to 32°C (90°F) and lows dropping to around -1°C (31°F).
JanFebMarAprMayJunJulAugSepOctNovDec242733455766716962523730
Data source: Temperature data for Groton 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 Groton

In Groton in September, the total precipitation amount is 99 mm (3.9 in) spread over a period of 10 days.

September Precipitation Trends in Groton

The chart displays monthly precipitation patterns in Groton, 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 Groton, September typically receives around 99 mm (3.9 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec89969112413710516311699155102103
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
Choose your preferred precipitation unit

September Humidity in Groton

In Groton in September, humidity is 78%. With an average temperature of 17°C (62°F), this humidity feels like a warm, enveloping blanket, making travel feel a bit sticky and heavy but also refreshing, as long as you're prepared with light clothing and plenty of water.

September Average Humidity in Groton

This chart illustrates the average monthly humidity levels in Groton, 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 Groton is approximately 78%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec90%90%87%88%82%79%78%76%78%84%89%86%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Groton

In Groton 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 Groton.

Maximum UV Index Levels in Groton for September

The chart shows the monthly maximum UV Index (UVI) for Groton 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 Groton typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec346810101098642
Data source: Groton 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 Groton Compares to Other Months

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

This table compares monthly weather conditions in Groton, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-4°C (25°F)88 mm (3.5 inches)90%moderate
February Weather-3°C (27°F)96 mm (3.8 inches)90%moderate
March Weather1°C (34°F)91 mm (3.6 inches)87%high
April Weather7°C (45°F)124 mm (4.9 inches)88%very high
May Weather14°C (57°F)137 mm (5.4 inches)82%very high
June Weather19°C (66°F)105 mm (4.1 inches)79%very high
July Weather21°C (71°F)163 mm (6.4 inches)78%very high
August Weather20°C (69°F)116 mm (4.6 inches)76%very high
September Weather17°C (62°F)99 mm (3.9 inches)78%very high
October Weather11°C (52°F)155 mm (6.1 inches)84%high
November Weather3°C (37°F)102 mm (4.0 inches)89%moderate
December Weather-1°C (30°F)102 mm (4.0 inches)86%low

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