The Atlantic Hurricane Season Comes to a Quiet Conclusion

Hurricane Dorian near peak intensity, September 2019  (Source: NOAA)

The 2019 Atlantic hurricane season saw its highest number of named storms since 2012 and the most Category 5 hurricanes in a single season in more than a decade.  Two hurricanes stand out this season more than any of the other storms that developed.  Check out this article I wrote for the WUSA9 website for more details.

Meteorological Fall Comes to a Close

Fall 2019 Comes to its Unofficial Conclusion Today

Meteorologists refer to the three-month period of September, October and November as "meteorological fall."  That differs slightly from "astronomical fall" that spans the period from the fall equinox to the winter solstice.  Astronomical fall is based on the position of the earth in relation to the sun, while the meteorological seasons are based on temperature cycles.

November 2019 is poised to finish as a cooler and drier than average month.  Through November 29, DC's average monthly temperature (considering daily high and low temperatures) was 3.6° below average.  Although last November finished 3.1° colder than average, it was also DC's wettest November on record with 7.57" of rain.  By comparison, only 1.37" has occurred so far this month, well below DC's November average of 3.17".  DC's warmest November temperature was 69° on November 11, while the coldest temperature was 26° on November 13.  The last time DC had two or more consecutive cooler than average Novembers was 2012 - 2014.

October 2019 was a tale of two weather extremes in the Nation's Capital.  It began as a very warm and dry month with 14 of the first 15 days warmer than average.  Washingtonians also endured the warmest October temperature on record with a sweltering 98° on October 2.  October also continued September's dry trend with only 0.14" through October 15.  Fortunately, the second half of the month was significantly wetter with a total of 6.52”.  That erased the moderate to severe drought conditions that had enveloped much of the DC Metro Area after a dry three-month period from July 15 - October 15 (when DC had a combined 7.01” rainfall deficit).

September 2019 finished as DC's third warmest and fourth driest on record.  Two record high temperatures were set in September for DC's highest such total since 1991.  September’s above average temperatures (25 out of 30 days warmer than average) only served to worsen the dry conditions in the Mid-Atlantic Region.  Only 0.25" of rain fell in September after a drier than average August.

Fall weather swung between extremes in the Nation's Capital this year.  Periods of warm and wet weather alternated with drier than average conditions and colder than average temperatures.  However, fall weather has little bearing on what the upcoming winter will be like.  For example, DC had four colder than average Novembers since 2010, with three of the subsequent winters finishing snowier than average (2013-2014, 2014-2015 and 2018-2019).  However, two of those winters were also warmer than average.  This November is well positioned to be DC’s coldest since 1997 and longtime Washingtonians may remember that the 1997-1998 winter had only 0.1” of snow.

NOAA's three-month outlook for December, January and February (meteorological winter) is for warmer and wetter than average conditions in the DC Metro Area.  Yet, the right ingredients have to come together only once to create an appreciable winter storm. 

Weather Quiz

Prior to 2019, when was the last time a November finished both colder and drier than average in Washington, D.C. ?

A.  1998

B.  2001

C.  2008

D.  2014

Hurricane Season 2019 Nears an End

Sunset is nearing for the 2019 Atlantic Hurricane Season

The 2019 Atlantic hurricane season concludes this Saturday, November 30.  It has been a busier than average one with 18 tropical storms, six of which became hurricanes including three major hurricanes.  Although hurricane season officially gets underway on June 1, this season got off to an earlier than average start for a fifth consecutive year when “Andrea” developed on May 20.

The strongest hurricane of the season, Hurricane Dorian, reached Category 5 intensity with maximum sustained winds of 185 mph and a minimum central air pressure of 910 millibars.   By comparison, standard sea level air pressure is approximately 1013 millibars.  Typically, the lower the air pressure, the stronger the storm is.  There is sometimes a lag between a fall in air pressure and commensurate rise in the sustained wind speeds of a tropical storm or hurricane.  Fortunately, Dorian had weakened considerably to a minimal Category 1 hurricane when it made landfall in North Carolina on September 6.  

This season’s other Category 5 Atlantic hurricane, Lorenzo, was the Atlantic’s easternmost Category 5 hurricane on record with sustained winds of 160 mph on September 29.  2019 is one of only seven seasons that two or more Category 5 storms developed in the Atlantic Ocean Basin.  Two also developed relatively recently in 2017 (Irma, Maria).  One Category 5 hurricane also developed in the Atlantic in 2016 (Matthew) and 2018 (Michael).  The Atlantic has now had at least one Category 5 hurricane in a record four consecutive years.

Another interesting fact about the 2019 Atlantic hurricane season is the difference between the number of tropical storms that developed, 18, and the number of which intensified into hurricanes, six.  When Tropical Storm Sebastien became a post-tropical storm this week (failing to reach hurricane intensity), 2019 became one of only four seasons since 1966 that a third or fewer of the tropical storms that developed became hurricanes.

The Saffir-Simpson hurricane wind scale ranks hurricanes from 1 to 5.  A minimal Category 1 storm has sustained winds of 74 – 95 mph, while a Category 5 hurricane has sustained winds of 157 mph/+.  A hurricane becomes “major” when it reaches Category 3 status with sustained winds of 111/+ mph.

The 2019 Atlantic hurricane season is also memorable for finishing as a busier than average one despite early expectations for a near average season.  Because a weak episode of El Nino dissipated by July, NOAA revised its seasonal forecast upward in early August.  No additional tropical storms are expected to develop before the season ends on Saturday.  The World Meteorological Organization (WMO) meets during the winter to determine which, if any; names will be retired for being destructive and/or deadly.

Thanksgiving Week

November 2019 is poised to finish as one of DC’s coolest in recent memory.  The first three weeks of the month have also been unusually dry.  Thanksgiving is the final Thursday of November and it fluctuates from year to year.  There has been a lot of diversity in Thanksgiving weather in the Nation’s Capital.

Thanksgiving falls on November 28 this year and that’s the latest calendar date it’s been since 2013.  DC’s average high/low temperatures on November 28 are 53°/37°.  Washingtonians had a cold Thanksgiving last year with a January-like high/low temperature of 42°/29°.  By comparison, DC’s warmest Thanksgiving temperature was on November 22, 2007 with a record high temperature of 77°.  No measurable rain has occurred in Washington, D.C. on Thanksgiving since 2011.  

Longtime Washingtonians may recall that it was 30 years ago when area residents last experienced a snowy Thanksgiving.  That Thanksgiving on November 23, 1989 had a two-day snow total of 3.5” that began the previous day.  November 1989 finished 1.6° colder than average in Washington, D.C. and was followed by DC’s coldest December since 1917.  In fact, 1989 remains the only time Washingtonians had both a snowy Thanksgiving and a snowy Christmas.

Fortunately for those who don’t like colder than average weather, some moderating temperatures are on tap during the upcoming week.  They still won’t be enough to offset how chilly the first few weeks of November have been in the Nation’s Capital.  Through November 22, DC’s average monthly temperature (combining daily high/low temperatures) is 5° below average.  Since it’s been a drier than average month so far with only 0.66” in DC, tonight’s rainfall will be quite beneficial.

Temperatures this month will finish significantly cooler than average despite some milder temperatures during the upcoming week.  The milder temperatures should be just enough, however, to prevent the month from finishing as one of DC’s coolest in recent decades.  National Airport opened in the early-1940s and that’s where weather measurements for the Nation’s Capital have been made since then.  DC’s 10 coldest November’s on record all occurred before that.  DC’s coldest November since 1941 was in 1976 with an average monthly temperature of 43.0°.

DC’s Ten Coldest November’s On Record (Source: National Weather Service)

1.  40.2° - 1880
2.  40.6° - 1901
3.  40.8° - 1873
4.  41.0° - 1875
5.  41.4° - 1910
6.  41.6° - 1903
7.  41.9° - 1887
8.  42.3° - 1871
9.  42.5° - 1872
10.  42.8° - 1911, 1917

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DC’s Coldest November’s at National Airport (Source: NWS)

1.  43.0° - 1976
2.  43.1° - 1995
3.  44.1° - 1951, 1996
5.  44.9° - 1962
6.  45.0° - 1967
7.  45.2° - 1954
8.  45.5° - 1955
9.  46.0° - 1984
10.  46.2° - 1947, 1997
12.  46.5° - 2018
13.  46.6° - 2008, 2012, 2013
16.  46.7° - 1943, 2000

Weather Quiz

True or False.

The Nation’s Capital has not had a “white” Thanksgiving and a “white” Christmas in the same year during the last 30 years.  Note: The snow doesn’t have to fall on the said holiday to make it an official “white” Thanksgiving or Christmas.