WEATHER NEWS: September D.C. weather outlook: Warmer and drier than normal
While it’s now meteorological fall (defined as September through November), September can be a summer sibling in many ways. Washington can experience strong heat and humidity at times during the ninth month.
In the coming weeks we expect it will generally feel more like summer than fall. For September overall, we project temperatures will average 1 to 2 degrees warmer than the monthly norm (which is 72.4 degrees — averaging daytime and nighttime temperatures).
Meanwhile, the dry conditions that commenced in August will probably continue. We’re predicting about one inch less rainfall than normal during the upcoming month (the 30-year average is 3.93 inches).
Computer model simulations generally favor near normal to above-normal temperatures and normal to below-normal rainfall for the first half of the month:
The projected above-normal temperatures in the Mid-Atlantic are modest, which means highs mainly in the mid- to upper 80s with moderately humid conditions.
Precipitation simulations are more mixed, but the models mostly lean toward drier-than-normal conditions in the Mid-Atlantic but above-normal amounts in the Southeast.
September is the peak of hurricane season, and it takes just the remnants from one storm to give rainfall totals a big boost. But so far this year, the Atlantic hurricane season has been remarkably quiet.
The National Weather Service updated its September outlook Wednesday and projects warmer-than-normal conditions over much of the United States, including the D.C. area. Its outlook calls for equal chances of above-normal, normal or below-normal rainfall.
The presence of La Niña tends to favor warm and dry weather in our region during the fall, but past events have resulted in variable outcomes, particularly for precipitation.
Recapping August and meteorological summer
We’re predicting September to be similar to August in a lot of ways. August finished 1 degree hotter than normal, and it was on the dry side.
The average temperature of 80.4 degrees ranked as the 12th-hottest August on record. The monthly rainfall of 2.42 inches was 0.83 inches drier than normal, and the 49th driest on record (since 1871).
Our August outlook called for an average temperature between 79 and 80 degrees, and so was just slightly off. Our rainfall projection of 3.25 to 6.25 inches was too aggressive.
Washington’s summer, by the meteorological definition of June through August, averaged 79.2 degrees, which is 0.3 degrees above the recent 30-year normal. It marked the 15th-hottest summer on record, even though it was the coolest since 2017. Rainfall managed to record 1.21 inches more than normal, despite the dry August.
So far, 2022 is tracking slightly drier and cooler than last year, but slightly warmer and wetter than the recent 30-year average. For now, 2012 continues to be the hottest year ever recorded in Washington.
To this point, Washington has seen 36 days at or above 90 degrees, which is exactly normal. In a typical September, we would see four more, though we have a decent chance to exceed that this year.