Whether its meteorological fall that gets underway on September 1 or astronomical fall that arrives on September 23, autumn officially arrives in September. September is also the most active month of the Atlantic hurricane season because atmospheric and environmental conditions are the most favorable. The Mid-Atlantic coastline had a glancing blow from Hurricane Dorian, which had a destructive trek through the Bahamas earlier in the week.
Other tropical systems over the last 20 years have had
significant impacts in the Mid-Atlantic Region during September like Floyd in
1999 and Isabel in 2003. However, Dorian wasn’t such a storm for the DC
Metro Area. According to the National Weather Service, the Nation’s
Capital averages 3.72” of rain in September. Ten of the last 20
September’s have been wetter than average.
Many DC Area residents should remember that September 2018 was DC’s
fifth rainiest on record with 9.73”.
Average high/low temperatures in Washington, D.C. fall from
84°/67° on September 1 to 74°/57° on September 30. September’s hottest
temperature on record in the Nation’s Capital remains the blistering 104° high
on September 7, 1881. By comparison, DC’s coolest September temperature
is 36° from September 23, 1904. Early September can be quite hot,
however, as Washingtonians experienced earlier this week with a record high
temperature of 96° on September 4. That was DC’s hottest September
temperature in nearly three years.
DC residents have experienced at least one day of 90° heat
every September since 2010. Not surprisingly, Washingtonians endured
three of the five warmest Septembers on record over the last decade (2010,
2016, 2018). As the Nation’s Capital has gotten more developed and seen a
commensurate increase in automobile traffic, overnight low temperatures are
warmer than they used to be. There have been 15 record high-low September
temperatures in Washington, D.C. during the last two decades. A
“high-low” temperature means the daily low temperature on a particular day was
unusually warm. By comparison, the last time DC residents had a record
low temperature in September was in 1988.
September 2019 has gotten off to a warmer and drier than
average start in the Nation’s Capital. NOAA’s outlook for the month is
for near average temperatures with a small probability for a wetter than
average month. If September finishes as a wetter than average month in
Washington, D.C., then it would be the first time since 2010 – 2012 that the
Nation’s Capital has had consecutive wetter than average September’s.
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