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September Weather in Boston, United States

Last updated: June 24, 2025

In Boston, United States, the average temperature in September typically hovers around 26°C (80°F). During this time, temperatures can dip to a refreshing 14°C (57°F), while peaks may soar to a sizzling 38°C (101°F). Rainfall averages 110 mm (4.3 in) across 13 days, contributing to an average humidity level of 83%, creating a warm and balmy atmosphere.

September Temperature in Boston

In September in Boston, the average temperature is 26°C (80°F). The maximum can reach 38°C (101°F), while the minimum can drop as low as 14°C (57°F). It's an ideal time for travelers to enjoy warm weather while being prepared for cooler evenings.

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

The chart illustrates September temperature patterns in Boston, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Boston, September typically has an average temperature of 26°C (80°F), with highs reaching up to 38°C (101°F) and lows dropping to around 14°C (57°F).
JanFebMarAprMayJunJulAugSepOctNovDec535963687680818180736056
Data source: Temperature data for Boston 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 Boston

In Boston in September, the total precipitation amount is 110 mm (4.3 in) over the course of 13 days.

September Precipitation Trends in Boston

The chart displays monthly precipitation patterns in Boston, 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 Boston, September typically receives around 110 mm (4.3 inches) of precipitation spread over approximately 13 days.
JanFebMarAprMayJunJulAugSepOctNovDec72965280741571481371107350118
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Boston

In Boston in September humidity is 83%. With an average temperature of 26°C (80°F), this humidity feels like a warm, enveloping blanket that can make traveling quite uncomfortable; you may find yourself needing frequent breaks for hydration and cool shade as the thick air clings to your skin.

September Average Humidity in Boston

This chart illustrates the average monthly humidity levels in Boston, 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 Boston is approximately 83%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%82%80%76%73%74%80%79%83%77%84%88%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Boston

In Boston in September, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in Boston.

Maximum UV Index Levels in Boston for September

The chart shows the monthly maximum UV Index (UVI) for Boston 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 Boston typically reaches 10, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec589101111111110864
Data source: Boston 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 Boston Compares to Other Months

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

This table compares monthly weather conditions in Boston, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather12°C (54°F)72 mm (2.8 inches)85%moderate
February Weather15°C (60°F)96 mm (3.8 inches)82%very high
March Weather17°C (64°F)52 mm (2.1 inches)80%very high
April Weather20°C (69°F)80 mm (3.1 inches)76%very high
May Weather25°C (76°F)74 mm (2.9 inches)73%extreme
June Weather27°C (80°F)157 mm (6.2 inches)74%extreme
July Weather27°C (81°F)148 mm (5.8 inches)80%extreme
August Weather27°C (82°F)137 mm (5.4 inches)79%extreme
September Weather26°C (80°F)110 mm (4.3 inches)83%very high
October Weather23°C (74°F)73 mm (2.9 inches)77%very high
November Weather16°C (61°F)50 mm (2.0 inches)84%high
December Weather13°C (56°F)117 mm (4.6 inches)88%moderate

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