September is one of the warmer months of the year in Boston, with average highs near 18.3°C and lows around 10.4°C (mean 14.4°C). It is about average for rainfall, averaging 56 mm of rainfall and 83% 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 2023 — when the month averaged 17.3°C — while the coldest was 1986 at 11.7°C. Typical September days reach 18.3°C with nights near 10.4°C. The long-term trend is warming, about 0.3°C per decade.
September is about average for rainfall in Boston, averaging 56 mm of rainfall. The wettest September on record was 2000 with 127 mm, while the driest was 2014 at 13 mm.
Relative humidity in Boston during September averages 83%. The most humid September was 2000 at 87%, and the least humid was 1991 at 78%.
September receives about 3.1 kWh/m²/day of solar energy in Boston. The sunniest September was 1991 at 3.6 kWh/m²/day, and the cloudiest were 2000 and 2001 at 2.5.
Average wind speed in Boston during September is 3.6 m/s. The windiest September was 1983 at 4.6 m/s, while the calmest was 2014 at 2.4 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 13.8°C | 14.0°C | 14.6°C | 14.4°C | 15.4°C | +1.6°C |
| Avg High | 17.8°C | 17.9°C | 18.5°C | 18.5°C | 19.4°C | +1.6°C |
| Avg Low | 9.8°C | 10.2°C | 10.7°C | 10.2°C | 11.4°C | +1.6°C |
| Avg Rain | 52 mm | 65 mm | 55 mm | 50 mm | 59 mm | +7 mm |
September temperatures in Boston have risen by about 1.5°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 3.7°C (2003) to a record high of 29.3°C (2023).
Rainfall in September is about average for rainfall, averaging 56 mm, with a wettest year of 127 mm.
One of the best times to visit Boston
September is one of the best times to visit Boston. Expect days averaging 18.3°C and nights around 10.4°C (mean 14.4°C) — warmer than Boston's yearly average — with moderate rainfall (56 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 | 19.1°C | 14.9°C | 10.7°C | 24.4°C | 6.6°C | 52 mm | 80% | 4.1 m/s | 3.2 |
| 2024 | 18.2°C | 14.6°C | 10.9°C | 24.2°C | 5.5°C | 82 mm | 86% | 3.6 m/s | 2.7 |
| 2023 🔥 | 21.5°C | 17.3°C | 13.1°C | 29.3°C | 8.8°C | 64 mm | 83% | 3.3 m/s | 3.2 |
| 2022 | 18.8°C | 15.0°C | 11.2°C | 24.1°C | 6.3°C | 51 mm | 82% | 3.1 m/s | 3 |
| 2021 | 20.1°C | 16.1°C | 12.0°C | 26.5°C | 6.7°C | 61 mm | 85% | 3.1 m/s | 3.1 |
| 2020 | 18.6°C | 14.4°C | 10.3°C | 24.3°C | 6.4°C | 44 mm | 82% | 3.8 m/s | 3.4 |
| 2019 | 18.7°C | 14.5°C | 10.3°C | 22.9°C | 6.7°C | 91 mm | 82% | 3.7 m/s | 3.4 |
| 2018 | 18.6°C | 14.2°C | 9.7°C | 23.3°C | 4.8°C | 26 mm | 81% | 3.8 m/s | 3.2 |
| 2017 | 17.8°C | 13.8°C | 9.8°C | 21.5°C | 6.0°C | 72 mm | 85% | 3.7 m/s | 2.9 |
| 2016 | 20.4°C | 16.2°C | 12.0°C | 27.6°C | 7.1°C | 59 mm | 85% | 3.5 m/s | 3 |
| 2015 | 17.0°C | 12.9°C | 8.9°C | 20.1°C | 6.4°C | 35 mm | 83% | 3.1 m/s | 3.3 |
| 2014 | 19.4°C | 15.2°C | 11.0°C | 22.0°C | 7.3°C | 13 mm | 84% | 2.4 m/s | 3 |
| 2013 | 17.9°C | 13.9°C | 9.9°C | 24.5°C | 5.7°C | 30 mm | 84% | 3.3 m/s | 3 |
| 2012 | 17.7°C | 13.5°C | 9.2°C | 25.2°C | 6.1°C | 50 mm | 82% | 4.1 m/s | 3.3 |
| 2011 | 19.8°C | 15.5°C | 11.2°C | 26.0°C | 7.7°C | 35 mm | 80% | 4.2 m/s | 3.2 |
| 2010 | 17.8°C | 14.1°C | 10.4°C | 21.8°C | 5.9°C | 87 mm | 84% | 3.9 m/s | 3 |
| 2009 | 18.4°C | 14.5°C | 10.6°C | 23.7°C | 7.8°C | 17 mm | 83% | 3.8 m/s | 3.2 |
| 2008 | 17.5°C | 13.9°C | 10.3°C | 20.7°C | 7.0°C | 61 mm | 85% | 3.3 m/s | 2.7 |
| 2007 | 17.9°C | 14.1°C | 10.4°C | 22.0°C | 6.2°C | 32 mm | 84% | 3.9 m/s | 3.2 |
| 2006 | 20.9°C | 16.9°C | 12.8°C | 24.9°C | 9.1°C | 75 mm | 85% | 3.4 m/s | 3.3 |
| 2005 | 19.7°C | 15.5°C | 11.3°C | 24.3°C | 6.1°C | 53 mm | 84% | 3.4 m/s | 3.2 |
| 2004 | 18.5°C | 14.6°C | 10.6°C | 24.6°C | 6.4°C | 45 mm | 84% | 4.4 m/s | 3.3 |
| 2003 | 18.8°C | 14.2°C | 9.5°C | 23.2°C | 3.7°C | 26 mm | 81% | 2.7 m/s | 3.4 |
| 2002 | 18.2°C | 14.5°C | 10.8°C | 21.0°C | 8.6°C | 33 mm | 83% | 2.9 m/s | 3.1 |
| 2001 | 16.8°C | 13.3°C | 9.8°C | 19.9°C | 7.5°C | 83 mm | 85% | 4.3 m/s | 2.5 |
| 2000 🌧️ | 18.7°C | 14.9°C | 11.2°C | 24.4°C | 7.3°C | 127 mm | 87% | 3.6 m/s | 2.5 |
| 1999 | 20.1°C | 16.1°C | 12.0°C | 25.8°C | 8.9°C | 68 mm | 84% | 3.4 m/s | 3.1 |
| 1998 | 18.5°C | 14.8°C | 11.1°C | 21.7°C | 6.3°C | 65 mm | 86% | 3.7 m/s | 2.9 |
| 1997 | 18.1°C | 14.3°C | 10.5°C | 21.7°C | 7.6°C | 18 mm | 82% | 3.5 m/s | 3.2 |
| 1996 | 17.2°C | 13.7°C | 10.2°C | 21.6°C | 7.6°C | 20 mm | 81% | 4 m/s | 3 |
| 1995 | 17.4°C | 13.7°C | 10.0°C | 20.0°C | 4.2°C | 91 mm | 84% | 3.6 m/s | 2.9 |
| 1994 | 16.4°C | 12.9°C | 9.4°C | 20.0°C | 6.6°C | 105 mm | 85% | 4.3 m/s | 2.9 |
| 1993 | 16.2°C | 12.9°C | 9.5°C | 20.5°C | 5.4°C | 99 mm | 84% | 3.7 m/s | 2.6 |
| 1992 | 18.0°C | 13.8°C | 9.6°C | 22.0°C | 5.7°C | 81 mm | 82% | 3.8 m/s | 3.1 |
| 1991 | 19.6°C | 14.9°C | 10.2°C | 25.6°C | 6.0°C | 65 mm | 78% | 3.5 m/s | 3.6 |
| 1990 | 17.1°C | 13.3°C | 9.5°C | 23.3°C | 5.4°C | 35 mm | 78% | 3.7 m/s | 2.8 |
| 1989 | 18.8°C | 15.2°C | 11.5°C | 23.7°C | 7.7°C | 40 mm | 81% | 3.5 m/s | 3 |
| 1988 | 17.1°C | 13.3°C | 9.5°C | 23.0°C | 4.6°C | 38 mm | 83% | 4.2 m/s | 2.7 |
| 1987 | 17.7°C | 13.7°C | 9.7°C | 22.6°C | 5.0°C | 40 mm | 83% | 3.7 m/s | 3 |
| 1986 ❄️ | 16.0°C | 11.7°C | 7.4°C | 20.3°C | 4.1°C | 22 mm | 82% | 3 m/s | 3.3 |
| 1985 | 18.6°C | 14.3°C | 10.1°C | 23.4°C | 6.5°C | 29 mm | 84% | 3.5 m/s | 3.1 |
| 1984 | 17.1°C | 13.4°C | 9.8°C | 23.6°C | 6.5°C | 85 mm | 83% | 4 m/s | 2.7 |
| 1983 | 17.4°C | 13.6°C | 9.8°C | 22.2°C | 5.5°C | 72 mm | 83% | 4.6 m/s | — |
| 1982 | 18.7°C | 14.4°C | 10.1°C | 24.6°C | 6.3°C | 56 mm | 84% | 3.4 m/s | — |
| 1981 | 18.7°C | 14.7°C | 10.7°C | 23.0°C | 7.3°C | 86 mm | 83% | 3.8 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 18.3°C with lows near 10.4°C (mean 14.4°C), based on 45 years of NASA POWER data.
September averages 56 mm of rainfall in Boston, about average for rainfall. The wettest on record was 127 mm in 2000.
The hottest September reached 29.3°C in 2023. The coldest dipped to 3.7°C in 2003.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.5°C. Daytime highs moved from 18.1°C to 19.5°C and overnight lows from 10.1°C to 11.6°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 18.3°C daytime highs and 10.4°C at night.
Not quite — September is the 10th coolest month in Boston, averaging 14.4°C.
For September in Boston, pack light layers you can adjust through the day, with typical highs of 18.3°C and lows of 10.4°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 83% — quite humid.
Average wind speed in September is 3.6 m/s. The windiest September on record averaged 4.6 m/s (1983).
The wettest September on record was 2000 with 127 mm. On average, September sees 56 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.
