It was almost even drier. The 0.14 inches of rain that fell Monday, September’s final day, prevented the month from matching the record-low rainfall of 0.11 inches in September 2005.
September’s rainfall of 0.25 inches was 3.47 inches below average and the lowest tally of any month since March 2006, when just 0.05 inches fell. Because of the sudden onset of such dry conditions, the federal government declared a flash drought.
The lack of rainfall intensified the heat. Twenty-five of 30 days reached at least the 80s in Washington, nine of them hitting 90 degrees or higher (on average we see just three 90-degree days in September).
The average temperature of 76.5 degrees was 0.1 degree higher than June and warmer than a typical June. That temperature was also 5.5 degrees higher than the September 30-year average. This was still 0.6 degrees lower than the 77.1 from 1980 and fell short of the hottest September on record in 1881, when the average temperature was 78.2 degrees.
Five of the top 10 hottest Septembers on record have occurred since 2000.
Below is a summary of the monthly extremes in Washington:
The Washington area hit a few records in September; all of them were record highs:
Wednesday, Sept. 4: Washington hit 96 degrees (beating the record 95 degrees from 2018, 2008 and 1985) and Baltimore hit 96 degrees to tie the 1937 record.
Thursday, Sept. 12: All three airports hit record highs, with Washington’s 98 beating 96 from 1931 and 1895. Baltimore’s 97 degrees bested 1931′s 96 degrees, and Dulles’s 95-degree temperature tied that of 1998.
Monday, Sept. 23: Dulles nabbed another record high with 94 degrees beating the 93 degrees from 2005 and 2010.
Sunday, Sept. 29: Dulles did it again with a high of 89 degrees besting the 1986 record of 85 degrees.
September featured lots of hot and dry high-pressure zones elevating temperatures and keeping the rain away. Most of the United States was under the influence of this high pressure and also notched a hotter-than-average September:
The atmosphere across the Northern Hemisphere featured very weak steering currents, which helped these large chunky high pressure areas to essentially get stuck in the mid-latitudes. There are signs that the mid-latitude weather systems may finally get moving again in October but it may take a few weeks.
Our hot September moved 2019′s average temperature up in the rankings compared with the rest of this decade.
The year-to-date average temperature is tied for second warmest with 2017:
Because of the lack of rainfall, our year-to-date precipitation total slipped into the middle of the pack for years in the past decade:
On Aug. 3, we forecast a warm and somewhat dry September. In reality, it was extremely warm and dry. As a result, this forecast earns a B for being on the right track but missing the intensity.
We project warmer than normal temperatures this September and slightly below normal rainfall. We’re looking for temperatures about two to three degrees above normal and rainfall about 0.25 to 1.0 inches below normal.
Jason Samenow contributed to this report.