Boston weather in September
Temperature, sea and sunshine in September: long-term averages from 30 years of weather data, not a forecast.
Holiday weather in September
Excellent
Best time to visit: May – September
What is the weather like in Boston in September?
In September, Boston is warm: daytime highs average 22 °C, and nights cool down to about 15 °C. The sea averages 17.5 °C – bracing, so a wetsuit helps for longer swims. Expect around 6 hours of sunshine a day. Rain falls on about 8 days, adding up to 87 mm. All in all, September is an excellent month for a holiday in Boston.
September compared
How the weather changes from August to October. Tap a month to open it.
| AugustAug | SeptemberSep | OctoberOct | |
|---|---|---|---|
| Score | 82 | 82 | 66 |
| Day | 26° | 22° | 16° |
| Night | 19° | 15° | 9° |
| Sea | 19° | 18° | 14° |
| Sun | 7 h | 6 h | 5 h |
| Rain days | 9 | 8 | 10 |
More details for September
- Daylight
- 12 h 33 min06:23 – 18:56
- UV index
- 6 · highclear sky, noon (estimate)All months
- Muggy days
- 5 daysdew point 18 °C or moreAll months
- Wind
- 18 km/haverage daily peakAll months
- Cloud cover
- 53 %on averageAll months
- Hot days
- 1 day30 °C or moreAll months
- Snow days
- 0 days1 cm or more of fresh snowAll months
- Time zone
- UTC−4America/New_York
How the score comes together
- Temperatureweight 50 %100 %
- Sunshineweight 20 %53 %
- Few rainy daysweight 30 %70 %
Each factor is rated from 0 to 100 % and weighted for the travel style “City break”.
What to pack in September
- Wetsuit for longer swims
- Sunscreen
- A jumper for the evenings
- Rain jacket or umbrella
Boston in September: quick answers
Is Boston hot in September?
Warm rather than hot: in September, daytime highs in Boston average 22 °C and nights cool to about 15 °C.
Can you swim in Boston in September?
Only if you don't mind cold water: in September the sea averages just 17.5 °C. Comfortable swimming temperatures are not reached at any time of year.
Does it rain much in Boston in September?
Rain falls on about 8 days, adding up to 87 mm.
Boston month by month
The whole year in BostonAll destinations: USAWhere to go in SeptemberSea temperature in September
Climate averages 1996–2025, not a forecast. Data: Copernicus ERA5 / ERA5-Land via Open-Meteo.com (CC BY 4.0), NOAA OISST, WMO 1991–2020 (NOAA NCEI), GeoNames (CC BY 4.0). Sources & licences