September is one of the warmer months of the year in Boston, with average highs near 23.2°C and lows around 12.3°C (mean 17.8°C). It is about average for rainfall, averaging 98 mm of rainfall and 75% relative humidity across the period.
September is one of the warmer months of the year in Boston. Across 45 years of records, the warmest September in Boston was 2015 — when the month averaged 20.6°C — while the coldest was 1991 at 15.5°C. Typical September days reach 23.2°C with nights near 12.3°C. The long-term trend is warming, about 0.6°C per decade.
September is about average for rainfall in Boston, averaging 98 mm of rainfall. The wettest September on record was 1999 with 222 mm, while the driest was 2014 at 34 mm.
Relative humidity in Boston during September averages 75%. The most humid September was 2011 at 85%, and the least humid was 1983 at 66%.
September receives about 4.2 kWh/m²/day of solar energy in Boston. The sunniest Septembers were 1984, 2007 and 2015 at 4.7 kWh/m²/day, and the cloudiest were 1993, 1996 and 2018 at 3.5.
Average wind speed in Boston during September is 0.5 m/s. The windiest Septembers were 2022, 2023 and 2024, among others at 0.5 m/s, while the calmest were 2011, 2014 and 2025, among others at 0.4 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 16.8°C | 17.0°C | 18.0°C | 18.7°C | 18.7°C | +1.9°C |
| Avg High | 22.4°C | 22.4°C | 23.5°C | 24.1°C | 23.8°C | +1.4°C |
| Avg Low | 11.2°C | 11.6°C | 12.4°C | 13.3°C | 13.5°C | +2.3°C |
| Avg Rain | 80 mm | 117 mm | 95 mm | 93 mm | 105 mm | +25 mm |
September temperatures in Boston have risen by about 1.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 1.4°C (1991) to a record high of 35.9°C (2002).
Rainfall in September is about average for rainfall, averaging 98 mm, with a wettest year of 222 mm.
One of the best times to visit Boston
September is one of the best times to visit Boston. Expect days averaging 23.2°C and nights around 12.3°C (mean 17.8°C) — warmer than Boston's yearly average — with higher rainfall (98 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 24.8°C | 19.1°C | 13.4°C | 30.1°C | 9.2°C | 83 mm | 74% | 0.4 m/s | 4.5 |
| 2024 | 24.3°C | 18.6°C | 12.9°C | 30.4°C | 10.6°C | 46 mm | 73% | 0.5 m/s | 4.3 |
| 2023 | 23.1°C | 19.0°C | 14.8°C | 32.7°C | 8.9°C | 156 mm | 84% | 0.5 m/s | 3.8 |
| 2022 | 23.2°C | 18.1°C | 12.9°C | 31.7°C | 7.1°C | 123 mm | 76% | 0.5 m/s | 4.1 |
| 2021 | 23.1°C | 18.5°C | 14.0°C | 27.3°C | 8.6°C | 185 mm | 82% | 0.5 m/s | 4 |
| 2020 | 24.6°C | 18.6°C | 12.7°C | 31.9°C | 5.9°C | 36 mm | 67% | 0.5 m/s | 4.4 |
| 2019 | 24.0°C | 18.2°C | 12.4°C | 30.6°C | 6.1°C | 35 mm | 72% | 0.5 m/s | 4.5 |
| 2018 | 23.7°C | 19.1°C | 14.6°C | 33.6°C | 8.1°C | 187 mm | 80% | 0.5 m/s | 3.5 |
| 2017 | 24.5°C | 19.2°C | 13.9°C | 31.9°C | 7.4°C | 93 mm | 76% | 0.5 m/s | 4.1 |
| 2016 | 25.0°C | 19.6°C | 14.1°C | 33.5°C | 5.6°C | 62 mm | 70% | 0.5 m/s | 4.1 |
| 2015 🔥 | 26.7°C | 20.6°C | 14.5°C | 34.4°C | 7.4°C | 116 mm | 71% | 0.5 m/s | 4.7 |
| 2014 | 24.2°C | 18.4°C | 12.5°C | 31.9°C | 5.7°C | 34 mm | 72% | 0.4 m/s | 4.5 |
| 2013 | 22.7°C | 16.9°C | 11.1°C | 33.5°C | 5.7°C | 95 mm | 75% | 0.5 m/s | 4.6 |
| 2012 | 22.8°C | 17.5°C | 12.1°C | 29.3°C | 6.8°C | 105 mm | 75% | 0.5 m/s | 4.2 |
| 2011 | 23.1°C | 18.5°C | 13.9°C | 28.7°C | 5.9°C | 143 mm | 85% | 0.4 m/s | 4 |
| 2010 | 24.7°C | 19.4°C | 14.1°C | 34.6°C | 7.6°C | 58 mm | 72% | 0.5 m/s | 4.1 |
| 2009 | 21.4°C | 16.2°C | 11.1°C | 26.3°C | 5.7°C | 53 mm | 78% | 0.5 m/s | 4.5 |
| 2008 | 22.3°C | 17.6°C | 12.8°C | 31.1°C | 7.1°C | 218 mm | 81% | 0.5 m/s | 4.1 |
| 2007 | 25.2°C | 18.9°C | 12.5°C | 34.0°C | 6.3°C | 63 mm | 69% | 0.4 m/s | 4.7 |
| 2006 | 21.8°C | 16.8°C | 11.7°C | 27.4°C | 4.9°C | 62 mm | 80% | 0.5 m/s | 4 |
| 2005 | 25.8°C | 19.8°C | 13.8°C | 31.7°C | 7.6°C | 60 mm | 70% | 0.4 m/s | 4.5 |
| 2004 | 23.0°C | 17.6°C | 12.2°C | 28.6°C | 6.7°C | 158 mm | 79% | 0.5 m/s | 4.2 |
| 2003 | 23.2°C | 18.1°C | 12.9°C | 28.4°C | 8.3°C | 92 mm | 79% | 0.4 m/s | 3.9 |
| 2002 | 25.6°C | 19.7°C | 13.7°C | 35.9°C | 7.3°C | 95 mm | 71% | 0.5 m/s | 4.3 |
| 2001 | 24.2°C | 18.3°C | 12.4°C | 31.9°C | 7.3°C | 71 mm | 69% | 0.5 m/s | 4.6 |
| 2000 | 22.8°C | 16.8°C | 10.9°C | 30.6°C | 2.0°C | 75 mm | 73% | 0.5 m/s | 4.2 |
| 1999 🌧️ | 23.8°C | 18.7°C | 13.5°C | 34.3°C | 6.9°C | 222 mm | 79% | 0.5 m/s | 3.9 |
| 1998 | 24.6°C | 18.3°C | 12.1°C | 30.0°C | 4.5°C | 62 mm | 71% | 0.4 m/s | 4.4 |
| 1997 | 22.8°C | 17.2°C | 11.6°C | 28.2°C | 4.4°C | 43 mm | 72% | 0.5 m/s | 4 |
| 1996 | 21.8°C | 17.3°C | 12.7°C | 30.0°C | 5.3°C | 180 mm | 80% | 0.5 m/s | 3.5 |
| 1995 | 22.4°C | 16.5°C | 10.6°C | 29.8°C | 4.9°C | 80 mm | 67% | 0.5 m/s | 4.3 |
| 1994 | 21.1°C | 16.2°C | 11.4°C | 28.2°C | 8.1°C | 137 mm | 77% | 0.5 m/s | 3.9 |
| 1993 | 22.2°C | 17.0°C | 11.8°C | 30.5°C | 3.3°C | 131 mm | 75% | 0.5 m/s | 3.5 |
| 1992 | 22.0°C | 16.6°C | 11.1°C | 29.0°C | 2.3°C | 89 mm | 74% | 0.5 m/s | 4.1 |
| 1991 ❄️ | 20.7°C | 15.5°C | 10.2°C | 29.7°C | 1.4°C | 177 mm | 77% | 0.5 m/s | 4.3 |
| 1990 | 22.2°C | 16.7°C | 11.2°C | 28.3°C | 3.5°C | 52 mm | 75% | 0.5 m/s | 4.2 |
| 1989 | 22.2°C | 16.8°C | 11.5°C | 32.3°C | 2.6°C | 117 mm | 77% | 0.5 m/s | 4.3 |
| 1988 | 22.2°C | 16.2°C | 10.2°C | 27.3°C | 4.5°C | 50 mm | 71% | 0.5 m/s | 4.5 |
| 1987 | 21.3°C | 16.6°C | 11.9°C | 28.4°C | 4.0°C | 176 mm | 79% | 0.5 m/s | 3.9 |
| 1986 | 21.9°C | 16.1°C | 10.3°C | 28.7°C | 5.1°C | 42 mm | 71% | 0.5 m/s | 3.9 |
| 1985 | 22.3°C | 16.8°C | 11.3°C | 28.5°C | 5.3°C | 97 mm | 78% | 0.5 m/s | 4 |
| 1984 | 21.6°C | 15.8°C | 10.0°C | 28.1°C | 5.0°C | 36 mm | 68% | 0.5 m/s | 4.7 |
| 1983 | 25.5°C | 19.1°C | 12.6°C | 33.4°C | 6.0°C | 37 mm | 66% | 0.5 m/s | — |
| 1982 | 22.6°C | 17.1°C | 11.5°C | 29.8°C | 8.3°C | 60 mm | 75% | 0.4 m/s | — |
| 1981 | 22.0°C | 16.5°C | 11.1°C | 28.8°C | 3.4°C | 101 mm | 73% | 0.5 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 23.2°C with lows near 12.3°C (mean 17.8°C), based on 45 years of NASA POWER data.
September averages 98 mm of rainfall in Boston, about average for rainfall. The wettest on record was 222 mm in 1999.
The hottest September reached 35.9°C in 2002. The coldest dipped to 1.4°C in 1991.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.6°C. Daytime highs moved from 22.8°C to 23.7°C and overnight lows from 11.3°C to 13.6°C over the same span.
September is one of the warmer months of the year in Boston and about average for rainfall, so plan for around 23.2°C daytime highs and 12.3°C at night.
Not quite — September is the 9th coolest month in Boston, averaging 17.8°C.
For September in Boston, pack light layers you can adjust through the day, with typical highs of 23.2°C and lows of 12.3°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 75% — moderately humid.
Average wind speed in September is 0.5 m/s. The windiest September on record averaged 0.5 m/s (1981).
The wettest September on record was 1999 with 222 mm. On average, September sees 98 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Boston behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
