Ranking July 2016

This July will finish among the hottest on record in the Nation’s Capital despite getting off to a remarkably cool start.  Washingtonians experienced 90-degree heat on 18 out of 19 days through July 31.  That includes Washington, D.C.’s first day of 100-degree heat in nearly four years when the temperature climbed to the century mark on July 25.  Baltimore and Dulles Airport also saw their first 100-degree temperatures since 2012.  

According to the National Weather Service, Washington, D.C. officially had 23 days at or above 90 degrees at National Airport since July 5.  That’s significantly above July’s average of 14 such days.  Washington, D.C.’s record for highest number of 90 degree days in a calendar month is 25 back in July 2011.  By comparison, July 2000 was Washington, D.C.’s coolest July since 1918 with only one day in the 90s and a monthly average temperature of 74.7 degrees (combining daily high and low temperatures).

The average high temperature in Washington, D.C. for much of July is 89 degrees, so temperatures in the low to mid-90s aren’t significantly warmer than average.  Also, Washington, D.C. experienced its second longest streak of consecutive hours with temperatures at or above 80 degrees at 134 hours from July 23 – 28, 2016.  That’s a good example of the city’s “urban heat island effect” where urban areas tend to remain warmer overnight than surrounding, more rural suburbs.

Although several days this month have brought showers and thunderstorms, July 2016 will finish with slightly below average monthly precipitation.  National Airport has officially measured 3.13” of rain through July 30 compared to the monthly average of 3.73”.  NOAA’s outlook for August calls for near average temperatures and near average precipitation in the Mid-Atlantic Region.

Washington, D.C.’s Warmest July’s (Degrees Fahrenheit)

1.  2011 – 84.5

2.  2012 – 84.0

3.  2010, 1993 – 83.1

5.  1999 – 83.0

6.  2016 – 82.7

7.  1987 – 82.6

8.  1980 – 82.3

9.  1955 – 82.1

10.  1988– 81.9

11.  1994 – 81.8

Washington, D.C. 90 Degree Days in July (number of days at or above 90 degrees)

2016 – 23 (Third highest July total behind 2011, 1993 and 1987 - tied with July 1988)
2015 – 14
2014 – 9
2013 – 11
2012 – 22
2011 – 25 (Broke DC’s monthly record of 24 from July 1993 and July 1987)
2010 – 20
2009 – 7

Hurricane Season Update

2016 Tropical Storm and Hurricane Tracks    (Source: NOAA)

Although the hurricane season doesn’t typically get busy until mid-August, this season is different.  After getting off to a record start with the earliest observed fourth named storm on record, things have gotten really quiet in the tropics.  That’s despite exceptionally warm sea surface temperatures and the dissipation of last winter’s major El Nino event.

Conditions during El Nino tend to preclude tropical development in the Atlantic Ocean since they bring cooler sea surface temperatures and an increase in wind shear in the tropical Atlantic.  Tropical storms and hurricane require warm ocean water and light winds to develop.  Although hurricane season starts on June 1, the first two months of the season tend to be quiet as the ocean water warms.  Conversely, the two month period from mid-August to mid-October tends to be the most active portion of the Atlantic hurricane season.

Since Tropical Storm Danielle dissipated on June 21, the tropics have been quiet.  Although having no tropical storms or hurricanes during the month of July isn’t unusual in the Atlantic Ocean, it is a big swing in the opposite direction following the fast start to this season.  Some observers have partially attributed that to an intrusion of dry air from West Africa that tends to preclude tropical development in what is known as Saharan Air Layer or SAL. 

An absence of storms in July doesn’t necessarily correlate to whether or not the season will be above or below average.  For example, the 2012 season got off to a fast start with the fourth named storm – Debby – dissipating on June 27.  The next storm, Ernesto, didn’t develop until August 1, in what would turn out to be a busier than average hurricane season in the Atlantic Ocean.  On the other hand in 2009, the first named storm didn’t develop until mid-August, in what was a below average Atlantic hurricane season.

We are on the verge of setting a new record for longest period of time without a hurricane in the Gulf of Mexico.  If we get through tomorrow, July 30, without a hurricane in the Gulf then that will surpass the existing record of 1,047 days.  It’s important to point out that while a number of tropical storms have traversed the Gulf of Mexico during the last few years – including Colin and Danielle this season – there hasn’t been a hurricane in the Gulf since Hurricane Ingrid in September 2013.  NOAA will update its June outlook for the 2016 hurricane season in early August.