Feeling like fall

 

Looking north from Roosevelt Island

Last month finished as DC’s third consecutive cooler than average August for the first time in a decade. August 2025 was also DC’s driest on record with only 0.2” of rain, well below the monthly average of 3.25”

September features some of the best weather of the year in the nation’s capital as fall officially gets underway. Average daily high/low temperatures drop from 85°/69° on September 1 to 75°/59° by the end of the month. The amount of daylight continues to decline throughout September. Sunset will occur at 6:52 p.m. on September 30. The combination of reduced daylight and a lower sun angle contributes to the cooler average temperatures as September wears on. 

Five of DC’s 10 warmest September’s have occurred since 2005. DC’s hottest September temperature on record is 104° on September 7, 1881. Triple-digit heat during September is a rarity in the nation’s capital and has occurred only four times since 1871. The most recent instance was on September 2, 1980 (101°). By comparison, DC’s coolest September temperature is 36° from September 23, 1904.

Although Washington, D.C. averages 3.93” of September rainfall, the amount of rain can fluctuate wildly year-by-year. September can be a very wet month if decaying tropical systems bring appreciable rainfall. Such was the case with Floyd in 1999, Isabel in 2003 and Florence in 2018. This month can also be very dry in the nation’s capital. The driest September on record was in 2005 (0.11”). Ironically, it was followed by DC’s wettest October (9.41”).

Last September was a unique month in the nation’s capital having been drier than average despite there being rain on the final 10 days of the month. September 2024 was also the first since 2011 that the nation’s capital didn’t see any 90-degree heat. The cooler autumn weather that typically arrives in September is a relief to many Washingtonians following the so often hot and humid summer weather.

NOAA’s Climate Prediction Center expect this September to finish with near average temperatures and precipitation. That’s despite the cooler than average weather that’s expected during the first half of the month.