Climate averages 1991–2020
Dorchester weather
in September.
A warm, moderately wet month: the 4th warmest and the 6th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a warm month in Dorchester: daytime highs average 22.2°C and nights cool to about 14.4°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 88 mm of rain on roughly 8 days, which makes September a moderately wet month (the 6th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 32 min on an average September day.
The nearest other city in this atlas is Boston (7 km away). In September its highs average 22.4°C, about as warm as Dorchester, with 88 mm of rain.
Among the 498 cities listed in the United States, Dorchester ranks joint 449th of 498 for the warmest September highs and joint 324th of 498 for the driest September (rainfall, lowest first). The mean September high of those 498 cities is 26.9°C; Dorchester is 4.7°C cooler than that mean.
From September to October, average highs fall by 6.3°C to 15.9°C, and monthly rainfall rises from 88 mm to 108 mm.
The annual picture
September in context
Monthly precipitation
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Dorchester climate table
| Month | Average highHigh / low | Average low | Precipitation mm/month | Wet days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 1.7°C-6.3°C | -6.3°C | 94 | 10.0 | 9.59 h |
| February | 3.0°C-5.5°C | -5.5°C | 84 | 8.9 | 10.511 h |
| March | 6.7°C-1.9°C | -1.9°C | 116 | 11.1 | 11.912 h |
| April | 13.0°C3.8°C | 3.8°C | 100 | 11.0 | 13.313 h |
| May | 18.5°C9.5°C | 9.5°C | 81 | 10.6 | 14.615 h |
| June | 23.8°C15.0°C | 15.0°C | 87 | 10.1 | 15.215 h |
| July | 27.2°C18.6°C | 18.6°C | 73 | 9.6 | 14.915 h |
| August | 26.3°C18.1°C | 18.1°C | 85 | 9.1 | 13.914 h |
| September, selected | 22.2°C14.4°C | 14.4°C | 88 | 8.1 | 12.513 h |
| October | 15.9°C8.5°C | 8.5°C | 108 | 9.8 | 11.111 h |
| November | 9.9°C2.8°C | 2.8°C | 95 | 9.6 | 9.810 h |
| December | 4.6°C-2.4°C | -2.4°C | 115 | 10.8 | 9.29 h |
Precipitation (rain or snow, as water) is the average of the 30 separate monthly totals. A wet day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Boston in SeptemberUnited States · 7 kmHigh 22.4°C · Low 14.1°C · 88 mm rain
- Quincy in SeptemberUnited States · 8 kmHigh 21.9°C · Low 14.8°C · 88 mm rain
- Newton in SeptemberUnited States · 12 kmHigh 22.6°C · Low 14.4°C · 85 mm rain
- Lynn in SeptemberUnited States · 21 kmHigh 21.0°C · Low 14.8°C · 87 mm rain
- Brockton in SeptemberUnited States · 24 kmHigh 22.1°C · Low 14.7°C · 89 mm rain
- Lowell in SeptemberUnited States · 42 kmHigh 22.6°C · Low 13.8°C · 84 mm rain
- Lawrence (Massachusetts), United States in SeptemberUnited States · 46 kmHigh 22.7°C · Low 14.0°C · 84 mm rain
- Pawtucket in SeptemberUnited States · 53 kmHigh 23.1°C · Low 14.7°C · 89 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Dorchester) is explained once on the Dorchester year overview and on the Sources, method and limits page.
Boston and Quincy lie in the same rainfall cell, so their rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells.