September Weather in the Nation’s Capital

NOAA Expects A Lot of Warm Weather through mid-September

August 2018 finished as a warmer and wetter than average month in the Nation’s Capital.  DC’s hottest temperature during the month of August was 94° that occurred on four different days.  Last month’s coolest temperature was 63° on August 24.  Although no record high temperatures were set last month, several record high-low temperatures were set.  That mean on several occasions, daily low temperatures remained significantly warmer than average.  August’s average monthly temperature (including daily high and low temperatures) was 81°, almost 3° above DC’s average of 78.1°.

A total of 5.19” of rain fell at National Airport last month, almost double the August average of 2.93”.  Almost half of that rain came on August 21 when a daily record of 2.46” occurred.  Unlike August 2011 that was warmer and wetter than average, a significant amount of DC’s rainfall that month was the result of weakening Hurricane Irene.  No tropical systems impacted the DC Metro Area in August 2018.

September is the first month of meteorological fall that runs through the end of November.  Average temperatures fall considerably during the month of September in Washington, D.C.  Average high/low temperatures range from 84°/67° on September 1, but are 74°/57° on September 30.  According to NOAA, DC’s hottest September temperature on record is 104° on September 7, 1881.  Meanwhile, this month’s coolest temperature on record is 36° on September 23, 1904.  Hotter than average weather is expected much of this week with several days in the 90s ahead.  NOAA expects warmer than average weather to continue at least through the middle of the month.  

The Nation’s Capital averages 3.72” of rain in September and that makes it one of the wettest months of the year.  Part of that can be attributed to the fact that September is the busiest month of the Atlantic hurricane season.  There have been a number of occasions that decaying tropical systems have brought significant amounts of rain to the DC Metro Area in September.  That most recently occurred in September 2011 when the remnants of Tropical Storm Lee contributed to make it much wetter than average (8.84”).

September 2018 has also managed to get off to a wet start with 0.81” of rain at National Airport yesterday.  NOAA’s precipitation outlook for September is for an increased probability for wetter than average conditions in the DC Metro Area.  The last time Washingtonians had a warmer and wetter than average September was in 2012.