Weather Quiz

True or False.  

Over 90% of the last 25 Halloweens have been dry in the D.C. Metro Area.

Halloween in the Nation’s Capital

The end of October often features some of the nicest weather of the year in the Nation’s Capital.  DC’s average high/low temperatures on October 31 are 64°/46°, according to NOAA.  Despite a cooler than average second half of October, this year’s Halloween is likely to be a warmer than average day with high temperatures around 70°.

DC’s record high on October 31 is 85° in 1950, while the record low for the date is 26° and has occurred more than once, most recently in 1917.  Over the last 25 years, DC has had measurable rainfall on only two Halloweens in 2002 and 2009.  The warmest Halloween in recent times was in 2004 when the high/low temperatures were 79°/59°, respectively, at National Airport.  Meanwhile, DC’s chilliest Halloween over the last 25 years occurred in 2002 with high/low temperatures of 47°/38°.  That’s more characteristic of mid-December than late-October.

October 2018 has been a unique weather month in the DC Metro Area.  It got off to an exceptionally warm start with above average temperatures on the first 11 days.  Nine of the first 11 days of October featured high temperatures of 81°/+.  Since October 12, all but six days have featured at or below average high temperatures in Washington, D.C.  

When the weather pattern shifted earlier this month, the conversation about October 2018 becoming the warmest on record in the Nation’s Capital came to an end.  That said, this month will still finish with a warmer than average monthly temperature (combining daily high/low temperatures) since the first 11 days were so much warmer than average.  Meanwhile, four of the five October’s from 2013 – 2017 were at least 2.9° warmer than average.  It will be interesting to see where October 2018 finishes up.

In addition to the warm start to 2018 with six of the first nine months of the year being warmer than average, this has also been a very wet year in the Nation’s Capital.  For the first time since 2003, Washington, D.C. had at least six consecutive wetter than average months (April through September).  While the Nation’s Capital averages 3.40” of rain in October, this month will finish with less than that – making it the fourth consecutive drier than average October.  

Since Washington, D.C. has had 52.89” of rain so far this year, it already ranks among the Top Ten wettest years on record.  If merely average rainfall occurs in November and December, then 2018 will finish with 59.11” of rain making this the fourth wettest year on record.

Washington, D.C.’s Ten Wettest Years (Source: NOAA)

1.  61.33” (1889)

2.  60.83” (2003)

3.  60.09” (1878)

4.  58.17” (1886)

5.  57.54” (1948)

6.  54.49” (1937)

7.  52.95” (1891)

8.  52.92” (1906)

9.  52.59” (1877)

10.  52.03” (1942)

Strongest October Hurricanes

Hurricane Mitch near peak intensity on October 26, 1998  (Source: NOAA)

There have been some notorious Atlantic hurricanes in October.  Some have impacted the United States and some have not.  The Atlantic Ocean Basin includes the Gulf of Mexico and Caribbean Sea.

2005: Hurricane Wilma occurred during the busiest Atlantic hurricane season on record.  It was the fourth Category 5 hurricane of the season and the strongest hurricane on record in the Atlantic Ocean Basin.  It had maximum sustained winds of 185 mph and a minimum central air pressure of 882 millibars (mb).  By comparison, standard sea level air pressure is approximately 1013.25 mb.  Hurricane Wilma weakened and made landfall in southwest Florida as a Category 3 hurricane on October 24.

1998: Hurricane Mitch developed in the southwest Caribbean Sea.  It was the first Category 5 hurricane anywhere in the Atlantic Ocean Basin since Andrew in 1992.  At peak intensity, Mitch had sustained winds of 180 mph with a minimum central air pressure of 905 mb.  Mitch remains tied with 2007’s Hurricane Dean for being the eighth strongest Atlantic hurricane on record.   Hurricane Mitch was at Category 5 intensity for 33 consecutive hours, which made it the longest continuous Atlantic Category 5 hurricane since Hurricane David in 1979.  Mitch caused widespread flooding in Central America that resulted in a catastrophic death toll of more than 10,000 fatalities.

1988: At peak intensity, Hurricane Joan was a powerful Category 4 hurricane with sustained winds of 145 mph and 932 mb.  It was one of the rare storms that survived its trek across Central America and became a tropical storm in the Eastern Pacific.  Once Joan reached the Eastern Pacific, it was given a new name “Miriam” since different oceanic regions have different lists of tropical storm/hurricane names.  Joan also set a record in the Atlantic Ocean for farthest south (12° North latitude) a hurricane reached Category 4 intensity.  That record would stand until Hurricane Ivan in 2004.

1961: Hurricane Hattie was an unusually strong, late season storm reaching Category 5 intensity on October 30 in the southwest Caribbean Sea.  Its maximum sustained winds reached 160 mph with a minimum central air pressure of 920 mb.  Hattie would be the last Category 5 hurricane to form anywhere in the Atlantic until Beulah in September 1967.

Two other October hurricanes get an honorable mention.  Hurricane Hazel remains the only Category 4 hurricane to make landfall in North Carolina (on October 15, 1954).  Due to Hazel’s fast rate of speed, it remained a powerful system well-inland and brought Washington, D.C. its highest wind gust on record (98 mph).  More recently, on October 1, 2016, Hurricane Matthew became the first Category 5 Atlantic hurricane since 2007.  Despite being a considerably weaker storm by the time it impacted the southeastern United States, Matthew still caused widespread damage and flooding.

All of these hurricanes have had their names retired by the World Meteorological Organization.  That means there will never be another “Mitch” or “Matthew.”

Feeling Like Fall

Temperature Outlook for the End of October 2018  (Source: NOAA)

This October got off to the warmest start on record in the Nation’s Capital.  However, while this week will feature plenty of sunshine, temperatures will actually be cooler than average for most of the week in the DC Metro Area.  The expected high temperatures in the mid to upper 50s on Wednesday, Thursday and Friday are more characteristic of mid-November than late-October.

October 2018 has been a unique weather month so far.  High temperatures were 81° or warmer on nine of the first 11 days of the month, including DC’s first 90° temperature in five years on October 4^th.  But, high temperatures have been cooler than average on six of the nine days since October 13.  Consequently, October’s average monthly temperature (combining daily high and low temperatures) in the Nation’s Capital has dropped from 74.7° on October 13 to 66.4° today.  

With the exception of near average high temperatures today in the mid to upper 60s, temperatures will be cooler than average the rest of the week.  In fact, NOAA expects below average temperatures to continue for much of the next six to 10 days.  Nevertheless, it’s worth pointing out that four of the last five Octobers (2013 – 2017) have had monthly temperatures at least 2.9° warmer than average.

Given the warm September and warm start to October, leaves have been slow to start changing color.  However, the cooler than average temperatures and decreasing amount of daylight should hasten the fall colors.  The fall foliage doesn’t normally reach its peak until early November in the immediate DC Metro Area and there should be plenty of color by then.  

Washington, D.C. has had a total of 1.81” of rain since October 1.  Although the bulk of this week will be dry, there is an increasing potential for appreciable rainfall on Saturday due to an early-season Nor’Easter.  Any additional rainfall would put DC closer to its October average of 3.40”.  Ten of the last 20 October’s have been wetter than average, but that hides how streaky October rainfall has been in the Nation’s Capital.  Ten of the 13 Octobers from 2002 – 2014 were wetter than average, while the last three have been drier than average.

DC’s Warmest Octobers (Source: National Weather Service)

1.  67.1° - 2007
2.  65.2° - 1984
3.  64.9° - 2017
4.  64.7° - 1971
5.  64.5° - 1947
6.  64.4° - 1941
7.  63.4° - 1949
8.  63.3° - 1973
9.  63.2° - 1975, 1919
11.  63.1° - 2016
12.  63.0° - 1879
13.  62.9° - 2014, 1881
15.  62.8° - 1990
16.  62.5° - 1970

59.5° - Average