D.C.’s Punishing Heat Waves

 

Washington, D.C. had some memorable July heat waves over the last 10-15 years.  A “heat wave” is defined as a minimum of three consecutive days of 90°/+ heat.

2019:  There was a stretch of 12 consecutive days that reached at least 90° from July 11 – July 22.  D.C.’s hottest temperature during this period was 99° on July 21.  Highs during this 12-day heat wave reached at least 95° five times.  While no record highs were set at National Airport, this heat wave was D.C.’s longest since 2016.

2016:  A 13-day heat wave occurred from July 21 – August 2.  Highs reached at least 95° six times.  The hottest temperature at National Airport was a record-tying high of 100° on July 25.  That was D.C.’s first instance of triple-digit heat since 2012.  This heat wave helped July 2016 finish as D.C.’s seventh warmest on record.

2012:  Although it began in late-June, the majority of an 11-day heat wave continued through July 8.  High temperatures reached at least 100° on five of those days, including four consecutively.  What made matters were widespread power outages that followed the infamous June 29 derecho.  

2011:  There was a 16-day heat wave from July 18 – August 2 (D.C.’s longest since an 18-day heat wave in 1999).  Not only did highs reach 100°/+ on four days, but another 8 days featured highs of least 95°.  The hottest day during this memorable heat wave was 104° on July 29.  That was D.C.’s hottest temperature in nearly 14 years since it was 105° on August 17, 1997.

2010:  The most significant heat wave of the summer occurred from July 14 – July 25.  During this 12-day stretch, the Nation’s Capital had five days with highs of at least 95° with the hottest day being 101° on July 24.  Following a near record high of 99° on July 25, this heat wave came to a rather abrupt end with widespread severe weather across the D.C. Metro Area.

Notable July Hurricanes

 

Hurricane Chris over the North Atlantic, July 2018  (Source: NOAA)

The last July hurricane in the Atlantic Ocean Basin was minimal Hurricane Elsa last year.  That’s not unusual because July is often one of the quieter months of the Atlantic hurricane season that spans from June through November.  However, that doesn’t mean there haven’t been some memorable July hurricanes.  Here are some of the more significant ones.

Chris (2018):  Although not a particularly strong or destructive hurricane, I’m partial to mentioning my namesake storm.  “Chris” first appeared on the list of names for Atlantic tropical systems in 1982.  It has been a named storm every six years since then and was a hurricane three times, most recently in 2018.  On July 11, 2018, Hurricane Chris reached its peak intensity as a Category 2 storm with sustained winds of 105 mph.  Fortunately, it was a safe distance off the East Coast there weren’t any major impacts.

Hurricane Emily (2005) – Emily broke several records during the epic 2005 Atlantic hurricane season.  Emily was the earliest Category 5 hurricane on record to form (July 16).  It remains the only July Category 5 hurricane ever observed in the Atlantic.  At peak intensity, Emily had sustained winds of 160 mph with a minimum central air pressure of 929 millibars – the lower the air pressure the stronger the storm is.  Standard sea level air pressure is approximately 1013 millibars (mb).  Emily’s remnants brought south Texas some beneficial rainfall and a few tornadoes.

Hurricane Dennis (2005) – Dennis was a powerful Category 4 hurricane at peak intensity with sustained winds of 150 mph and a minimum central air pressure of 930 mb.  Dennis reached peak intensity on July 10 in the Gulf of Mexico.  After causing extensive damage in Cuba, it made landfall on the Gulf Coast as a Category 3 hurricane.  Dennis would become the first of five hurricanes to have their names retired by the World Meteorological Organization following the 2005 season – the highest such number on record.  Hurricanes and tropical storms have their names retired for being exceptionally damaging or deadly. 

Bertha (1996):  Bertha was an early season Cape Verde hurricane.  At peak intensity, it was a Category 3 storm with sustained winds of 115 mph and a minimum central air pressure of 960 mb.  However, it weakened to a Category 2 storm with sustained winds of 105 mph prior to its landfall in North Carolina.

There was another Hurricane Bertha in July 2008.  This version was even stronger with sustained winds of 125 mph and a minimum pressure of 952 mb.  Fortunately, it never made landfall and remained over the open Atlantic Ocean.  But it was a long-lasting system, having been a tropical storm or hurricane from July 3 – July 20.  That made the 2008 version of Bertha the longest lasting July tropical storm or hurricane on record in the Atlantic Ocean.

D.C.’s Warmest and Wettest Month of the Year

 

NOAA's Temperature Outlook for July 2022

June 2022 finished as a slightly cooler and drier than average month in the Nation’s Capital.  That’s a rare combination given how warm and wet the last 10 – 15 years has been in Washington, D.C. 

July is D.C.’s hottest month of the year based on average high/low temperature kept by NOAA.  Average daily high/low temperatures in Washington, D.C. range from 89°/71° on July 1 to 89°/72° on July 31.  However, the hottest time of the year occurs from July 11 - 27 when D.C.’s average high/low temperatures are 90°/73° from July 11 – July 27.  NOAA’s climate averages are based on 30 years of data and are updated every decade.  Last spring NOAA updated its averages to reflect the period of 1991-2020 that replaced the previous data set of 1981-2010.

During the previous data set, D.C.’s hottest average daily high temperature was 89° for most of July.  However since the 2010s were a much warmer decade than the 1980s, D.C.’s average daily high temperature for most of July went up from 89° to 90°.  That shouldn’t surprise longtime Washingtonians as six of D.C.’s 10 hottest July’s have occurred just since 2010 based on NOAA data.  Consequently, D.C.’s average July temperature (combining daily high/low temperatures) for the 30-year period of 1981-2010 was 79.8°, but rose to 81.0° when updated to reflect the period of 1991-2020.

D.C.’s hottest July temperature on record is 106° from July 20, 1930.  That’s tied with a date in August for D.C.’s hottest overall temperature.  More recently, D.C.’s second hottest temperature of 105° occurred on July 7, 2012.  No triple-digit July heat has occurred in Washington, D.C. since 2016.  D.C.’s coolest July temperature of 52° has occurred several times, most recently on July 4, 1933.

July’s new monthly rainfall average of 4.33” also makes it D.C.’s wettest month of the year.  That represents a significant increase over the old average of 3.73” from the period of 1981-2010.  Two of D.C.’s 10 wettest July’s have occurred at National Airport quite recently in 2017 and 2018.  NOAA’s Climate Prediction Center is expecting July 2022 to be a warmer and wetter than average month in the D.C. Metro Area.  That would continue the recent trend in the Nation’s Capital.