Boston Weather in September

Boston, Massachusetts usually gets its last blast of really hot weather for the year in September. Most days though, have milder temperatures. And relatively few days this month have rain.

This page gives detailed information on the typical September temperature, precipitation, sun, humidity, wind and storms for Boston. The numbers here are historical averages based on climate data gathered at Boston's Logan International Airport, located on the waterfront next to Boston Harbor.

Temperature Weather iconTemperature

73 °F September average high 23 °C
58 °F September average low 15 °C
20 days 70 °F max. or more (21 °C)
19 days 60 °F min. or less (16 °C)

Usually every day in September warms to over 60 degrees Fahrenheit (16 degrees Celsius) in Boston. The city averages 1 day this month when the thermometer reaches into the 90s °F (over 32 °C). Temperatures above 100 °F (38 °C) are not expected here during September.

This month the thermometer dips to 50 °F (10 °C) or below on an average of three nights. A temperature as cold as 40 °F (4 °C) occurs in September about once a decade.

Rainy Weather iconRain

3.6 in total precipitation 90 mm
9 days of rain

Half the time, the Boston receives 1.9 to 4.5 inches (48 to 115 mm) of rainfall in September. One in four years has drier weather, while another one in four is wetter. None of the precipitation falls as snow.

Sunny Weather iconSun

63 % sunshine
10 days clear skies

The sun's rays reach the ground in Boston during 63 percent of daylight hours on average in September, for a total of 235 hours in the month. Typically on 10 days this month the sky is mainly clear, with at most 30 percent cloud cover.

Sunlight in September at Boston lasts for 12 hours and 26 minutes a day on average. The longest day of the month is the 1st with 13 hours and 7 minutes of daylight. By the end of the month, the days have shortened to 11:46 from sunrise to sunset. These durations of daylight can vary by a minute or two from year to year.

Humid Weather iconHumidity

72 % September average humidity

The relative humidity in Boston during September usually peaks at 82 percent in the morning then drops to 59 percent by early afternoon. September is Boston's most humid month.

Local Time1 am4 am7 am10 am1 pm4 pm7 pm10 pm
Humidity % 80 82 79 65 59 62 71 76

Windy Weather iconWind

11.2 mph September wind speed average 18.0 kph

September is slightly less windy than most other months in Boston.

Stormy Weather iconStorms

2 days rainfall of 0.5 inches (13 mm) or more
1 day with thunderstorms in September
6 % chance a named storm approaches

There's a 2 percent probability that a hurricane will approach within 100 miles (165 km) of Boston during September. The chance of a major hurricane (category 3 to 5) reaching the area is 1 percent.


The weather data here are long-term averages provided by the US National Centers for Environmental Information (NCEI). Temperature and precipitation are 1991-2020 normals while humidity and thunderstorms are 1961-1990 normals. The named storm probabilities come from the Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division.

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