September Gets Underway

 

A Stellar Start to Labor Day Weekend

August 2021 finished as a warmer and considerably wetter than average month in the Nation’s Capital.  Measurable rainfall occurred on 17 days last month, including on nine consecutive days from August 13 – August 21.  The 9.07” of rain at National Airport made last month Washington, D.C.’s ninth wettest August ever and wettest since 1967 (9.17”).

August 2021 also finished with 19 days that were warmer than average, including 16 days in the 90s.  That helped the Nation’s Capital finish with its fourth consecutive warmer than average August, with a monthly average temperature 1.5° above average.  Although September got off to a very wet start with the remnants of Hurricane Ida across the D.C. Metro Area, the weather heading into Labor Day Weekend has been stellar. 

Average daily high/low temperatures fall in the Nation’s Capital from 84°/67° on September 1 to 74°/57° by September 30.  In a refreshing change of pace, no 90° heat is expected in the D.C. Metro Area during the first week of September.  That’s in contrast to recent September’s that have featured a number of 90° days.  It’s too early to say whether or not this September could become D.C.’s first without any 90° heat since 2009.

Washington, D.C.’s hottest September day on record was September 7, 1881, with a high of 104°.  By comparison, D.C.’s coolest September temperature was 36° on September 23, 1904.  Weather records in the Nation’s Capital date back to 1871.  However, since World War II, measurements for the Nation’s Capital have been made at National Airport compared to down prior to that.  The hottest observed September temperature at National Airport was 101° on September 2, 1980 (also the last time 100° Washingtonians have experienced triple-digit heat in September), while the coolest September temperature at National remains 38° on September 30, 1942.

The Nation’s Capital averages 3.93” of rain in September, with nine of the last 20 Septembers being wetter than average.  September rainfall can fluctuate significantly depending on whether or not a tropical system impacts the region.  For example, September 2003 (Isabel), 2011 (Lee) and 2018 (Florence) were all wetter than average with former tropical systems a key reason why.  By comparison, Washington, D.C.’s driest September on record occurred in 2005 (0.11”), while only 0.25” fell in September 2019.  NOAA expects this month to be wetter than average in the Nation’s Capital.  This month has already gotten off to a wet start with the significant, flooding rainfall from the remnants of Hurricane Ida on September 1.