Summer 2020 Wrap

This summer has featured plenty of memorable weather in the Nation's Capital.  It’s been another warmer than average summer that didn't see any triple-digit heat.  While June was relatively benign, July and August were each quite hot and wet in the DC Metro Area.

August is ending on a rainy note today with a chance DC could climb into the Top 10 for wettest August's.  As of August 30, the Nation's Capital had 8.33" of rain and needs to get to 8.92" to tie 2011 for tenth wettest August.  Although today will be DC's seventeenth August day with measurable rainfall, more than half of this month's rain has occurred on just three days that saw a combined 4.97" (August 4, August 16 and August 28).  

Hurricane Isaias had impacts in the DC Metro Area after making landfall in North Carolina on August 3.  Meanwhile, the remnants of Laura made themselves felt late in the month.  Despite all the rain, this month will finish roughly 1.5° warmer than average.  In fact, five of the last six August’s have been warmer than average in the Nation’s Capital.

The first cooler than average day of July 2020 didn't occur until July 31.  Last month finished as DC's second hottest on record, just 0.1° behind 2012.  Although it was so hot in the Nation's Capital last month, there wasn't any triple-digit heat.

Rather, last month was consistently hot with a new DC record for most 90° days (28) to occur in any month.  Low temperatures didn't fall below 70° once in July.  While DC's hottest July 2020 temperature was 99°, Baltimore got to 100° (twice).  DC had 6.51" of rain last month (2.78" above average), with a daily record of 2.04" on July 7.

June 2020 finished with a monthly average temperature (combining daily high and low temperatures) of 77°, making it DC's warmest June since 2017.  There were nine days with highs in the 90s, with the hottest temperature being 93° on June 3 and June 27.  By comparison, DC's coolest June temperature was 54° on June 1.  It was DC's eleventh consecutive warmer than average June.  Washingtonians saw 3.51" of rain in June (0.27" below average).

If July and August have felt especially dreary in the Nation's Capital, that's because there has been a lot of rain.  There is a surplus of more than 8” since July 1.  Including today, there have been 29 days with measurable rainfall in the Nation’s Capital since July 1.  NOAA’s Climate Prediction Center expects September to be warmer than average in the DC Metro Area with near average rainfall.

How Does August 2020 Measure Up ?

If it seems like August has been a wet month, there’s good reason.  There have been 16 days this month with measureable rainfall in the Nation’s Capital which produced a total of 8.33” (5.58” above average).  A large portion of that is attributed to the two tropical systems that impacted the DC Metro Area.

Category 1 Hurricane Isaias made landfall in North Carolina on August 3 and quickly moved northward.  It brought a significant amount of rain and severe weather to the DC Metro Area.  What’s more, Isaias spawned roughly three dozen tornadoes in the United States.  Record-setting rainfall also occurred at both National and Dulles Airports on August 4.  Washington, DC had a combined rainfall total of 3.01” during the first four days of August – more than DC averages (2.93”) during the entire month.

The middle of the month was also wet in the DC Metro Area.  There was measurable rainfall on six consecutive days, from August 12 – August 17, with widespread showers and thunderstorms each day.  While a total of 2.29” of rain occurred in that time in DC, it was even wetter in Baltimore with 6.06” at BWI Airport.  In fact, this month is poised to finish as Baltimore’s fourth wettest August with 11.69” as of August 29.  With more rain in the forecast tomorrow, Dulles Airport could finish with its third wettest August.  On top of everything, the remnants of Hurricane Laura brought more rainfall to the DC Metro Area yesterday. 

August 2020 will finish as a warmer than average month in the Nation’s Capital for the fifthteenth time in the last 20 years.  While this month’s total of seven 90° days is below DC’s average of roughly 10 such days, what’s made the difference is how warm overnight low temperatures have been.  Low temperatures remained in the 70s on 22 of the first 28 days of August and that’s unusual.  In fact, the Nation’s Capital set a record for longest stretch of consecutive days temperatures remained 70°/+ from June 27 – August 15. 

Temperatures today will be near average with highs in the mid-80s, but will be below average tomorrow with highs near 80° and the prospect of more rain.  Nevertheless, DC will finish August 2020 with a monthly average temperature (combining daily high and low temperatures) more than a degree above average.  DC’s warmest temperature this month was 93° on August 27 and August 28, while the coolest temperature was 66° on August 16 and August 17.

The outlook for September 2020 from NOAA’s Climate Prediction Center is for warmer than average temperatures in the DC Metro Area with a near average amount of rain.

DC’s Ten Wettest August’s (Source: NOAA)

1.  14.41” (1928)
2.  14.36” (1906)
3.  14.31” (1955)
4.  12.93” (1875)
5.  9.91” (1933)
6.  9.75” (1905)
7.  9.49” (1942)
8.  9.17” (1967)
9.  9.00” (1948)
10.  8.92” (2011)

"Laura" is the Latest Destructive Gulf Hurricane

Hurricane Laura nearing the Louisiana Coast (Source: WUSA9)

Hurricane Laura not only became the Atlantic's first major hurricane of 2020, but it also intensified at an exceptionally fast rate.  Its sustained winds increased in a 24-hour period from a minimal 75 mph Category 1 hurricane to a powerful 140 mph Category 4 as it accelerated northwestward in the Gulf of Mexico.  Similar to Hurricane Michael in October 2018, Laura continued to intensify right up until it made landfall late last night near the Texas/Louisiana border.

Hurricane Michael also tracked through the Gulf of Mexico and had very favorable conditions for rapid intensification.  Consequently, Michael intensified to a rare Category 5 storm with sustained winds of 160 mph and a minimum central air pressure of 919 millibars (millibars is abbreviated as "mb").  By comparison, Laura's peak intensity was as a strong Category 4 hurricane with sustained winds of 150 mph and a minimum air pressure of 937 mb.  Standard sea level air pressure is 1013.25 mb.  Based on Laura’s 150 mph winds at landfall, it tied with an unnamed 1856 hurricane as strongest to make landfall in Louisiana.  Laura also had the fourth lowest air pressure (938 mb) of any landfalling hurricane in Louisiana (behind 2005’s Katrina, 920 mb, the 1856 “Last Island” hurricane, 934 mb, and Rita, 937 mb, also 2005).

Although Hurricane Laura weakened overnight since making landfall, its devastating impacts will be far-reaching.  In addition to a dangerous storm surge along the Gulf Coast, flooding rainfall, exceptionally high winds and isolated tornadoes will continue.  While hurricane-spawned tornadoes aren't usually as strong as tornadoes spawned by supercell thunderstorms, they're even more dangerous in one regard.  That's because tornadoes in landfalling tropical systems are often obscured by heavy rainfall.  Laura will continue to weaken as it moves further inland and will no longer be a hurricane or tropical storm.  Its remnants will bring the DC Metro Area heavy rain and gusty winds on Saturday.  

Laura's track through the Gulf of Mexico was similar to other significant hurricanes that have occurred during the last 15 years.  The 2005 Atlantic hurricane season was the busiest on record with 28 named tropical storms and 15 hurricanes.  Of those 15 hurricanes, a season record of four Category 5 hurricanes developed, most notably Hurricanes Katrina and Wilma.  Also, Hurricane Rita occurred just a few weeks after Katrina and was also a Category 5 hurricane over the open Gulf of Mexico.  Fortunately, it weakened to a Category 3 storm before it made landfall in a similar location to Laura near the Texas/Louisiana border.

Hurricane Ike in 2008 was another storm that made landfall in eastern Texas, a little further west than Laura and Rita, as a strong Category 2 storm with sustained winds of 110 mph.  While not as strong at its time of landfall as Laura or Rita were, Ike's wind field was quite large and that resulted in more damage than it otherwise would have.  Since Hurricane Laura is ongoing, it will be some time its toll in terms of damage and loss of life is determined.  What can be assumed now is that the World Meteorological Organization will likely retire the name “Laura” after the hurricane season ends for being so destructive and deadly.