Late Season 90° Heat

NOAA's Temperature Outlook for the Second Week of October

Temperatures in the Nation’s Capital have reached the 90s on eight days so far this month.  That’s the highest such total since September 2010 when Washingtonians sweat through 10 days of 90° heat.  Two record high temperatures have also been set at National Airport this September for the first time since 1991.

The frequency of the 90° heat has been spread out fairly evenly throughout September.  There haven’t been more than two consecutive days of 90° heat in the Nation’s Capital since September 1.  That means there haven’t been any “heat waves” which are defined as a minimum of three or more consecutive days of temperatures at or above 90°.  It is somewhat ironic that September 2019 has been so warm in the DC Metro Area without an official heat wave.

NOAA’s Climate Prediction Center expects these warm temperatures to continue into early-to -mid October for much of the DC Metro Area.  Another day or two of 90° heat is even possible during the upcoming work week.  Any 90° heat in the Nation’s Capital in October is a very rare occurrence.  That’s because the sun angle is much lower than during the summer months.  That combined with the decreasing amount of daylight makes it more difficult to get very warm.  The latest in the year Washingtonians have experienced 90° heat is October 11.

There have been only five Octobers dating back to 1994 that DC residents have had temperatures in the 90s.  The most recent occurrence was on October 4, 2018.  Over the same 25-year time period, DC’s last 90° day of the year occurred in August eight times, most recently in 2011.

September 2019 is well-positioned to finish as one of DC’s warmest on record.  That’s because all but five days since September 1 have been warmer than average.  This month will also finish as one of DC’s driest.  That will make this month the first time the Nation’s Capital has had a September that’s ranked among both the top five warmest and driest.