Climate averages 1991–2020
Wilmington (Delaware), United States weather
in September.
A warm, wet month: the 4th warmest and the wettest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a warm month in Wilmington (Delaware), United States: daytime highs average 24.6°C and nights cool to about 16.3°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 107 mm of rain on roughly 10 days, which makes September a wet month (the wettest month of the year). Daylight, from sunrise to sunset, lasts about 12 h 30 min on an average September day.
The nearest other city in this atlas is Philadelphia (40 km away). In September its highs average 25.1°C, about as warm as Wilmington (Delaware), United States, with 104 mm of rain.
Among the 498 cities listed in the United States, Wilmington (Delaware), United States ranks joint 325th of 498 for the warmest September highs and joint 418th of 498 for the driest September (rainfall, lowest first). The mean September high of those 498 cities is 26.9°C; Wilmington (Delaware), United States is 2.3°C cooler than that mean.
From September to October, average highs fall by 6.3°C to 18.2°C, and monthly rainfall falls from 107 mm to 91 mm.
The annual picture
September in context
Monthly rainfall
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
Wilmington (Delaware), United States climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 4.5°C-3.0°C | -3.0°C | 82 | 9.2 | 9.710 h |
| February | 6.1°C-2.4°C | -2.4°C | 76 | 8.7 | 10.711 h |
| March | 10.6°C1.2°C | 1.2°C | 105 | 10.7 | 11.912 h |
| April | 16.9°C6.8°C | 6.8°C | 92 | 10.5 | 13.213 h |
| May | 22.0°C12.4°C | 12.4°C | 89 | 10.8 | 14.314 h |
| June | 26.8°C17.7°C | 17.7°C | 99 | 10.4 | 14.915 h |
| July | 29.3°C20.7°C | 20.7°C | 99 | 10.9 | 14.715 h |
| August | 28.2°C19.9°C | 19.9°C | 100 | 10.4 | 13.714 h |
| September, selected | 24.6°C16.3°C | 16.3°C | 107 | 9.6 | 12.512 h |
| October | 18.2°C10.0°C | 10.0°C | 91 | 8.1 | 11.211 h |
| November | 12.1°C4.1°C | 4.1°C | 75 | 7.9 | 10.010 h |
| December | 6.9°C-0.3°C | -0.3°C | 100 | 9.0 | 9.49 h |
Rainfall is the average of the 30 separate monthly totals. A rain 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
- Philadelphia in SeptemberUnited States · 40 kmHigh 25.1°C · Low 16.3°C · 104 mm rain
- Camden in SeptemberUnited States · 42 kmHigh 25.0°C · Low 16.3°C · 99 mm rain
- Cherry Hill in SeptemberUnited States · 49 kmHigh 24.9°C · Low 16.4°C · 99 mm rain
- Reading, United States in SeptemberUnited States · 73 kmHigh 24.7°C · Low 15.2°C · 108 mm rain
- Trenton in SeptemberUnited States · 86 kmHigh 24.7°C · Low 15.7°C · 101 mm rain
- Allentown in SeptemberUnited States · 96 kmHigh 24.1°C · Low 14.1°C · 113 mm rain
- Bethlehem, United States in SeptemberUnited States · 99 kmHigh 24.1°C · Low 14.1°C · 109 mm rain
- Baltimore in SeptemberUnited States · 105 kmHigh 24.8°C · Low 16.6°C · 120 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 Wilmington) is explained once on the Wilmington (Delaware), United States year overview and on the Sources, method and limits page.