How are Things Looking in the Tropics?

Tropics are Generally Quiet on 7-29-15  (Source: NOAA)

Aside from getting off to an early start with Tropical Storm Andrea forming in May, the 2015 hurricane season has been rather quiet.  Although there have been three named storms so far, they have all been relatively weak and short-lived.  Most people are unaware of Tropical Storm Claudette which formed last week off the Mid-Atlantic Coast because it quickly moved out to sea and dissipated.  None of this season’s three tropical storms reached hurricane intensity.

June and July are typically among the quieter months of the hurricane season, with activity picking up in August.  However, current conditions in the tropical Atlantic Ocean remain inhospitable for tropical storm formation.  Sea surface temperatures aren’t as warm as they usually are this time of year and there has been an increased amount of wind shear – winds that change direction with height in the atmosphere.  Tropical storms and hurricanes weaken when they encounter wind shear or cooler water. 

Scientists generally attribute these unfavorable conditions to a developing El Nino event.  “El Nino” refers to the warming of the water in the central and eastern equatorial Pacific Ocean.  NOAA is forecasting a 90% chance that the developing El Nino will last through the 2015-2016 winter season.  El Nino has global repercussions and contributes to a busier than average hurricane season in the Eastern Pacific Ocean – west of Mexico.  Meanwhile, during an episode of El Nino, the Atlantic Ocean sees a below average number of tropical storms and hurricanes.

However, a below average number of tropical storms and hurricanes doesn’t mean none of them will be destructive or deadly.  For example, 1992 was a quieter than average hurricane season in the tropical Atlantic Ocean but was the year of Hurricane Andrew.  Andrew developed in August and was one of the strongest and most damaging hurricanes in U.S. history.
 
From 1995 through 2012, all but two seasons saw an above average number of named storms in the Atlantic Ocean.  Although NOAA will soon issue its August update to their hurricane season forecast, all indications are that the Atlantic Ocean will see its third consecutive below average hurricane season.

How Hot has 2015 Been?

Keeping cool at Great Falls (MD Side)

Today is the third anniversary of the last time the temperature reached 100 degrees in the Nation’s Capital.  2012 was the third consecutive summer that saw frequent triple-digit heat in Washington, D.C.  However, since then there has been a three year stretch without any 100 degree heat in the Mid-Atlantic Region.

This summer has already featured more 90 degree heat than all of last year combined.  Washington, D.C. averages 36 days of 90 degree heat in a given year and there have already been 27 such days through July 25.  There were only 24 such days last year.  National Weather Service data indicates that Washington, D.C.’s record number of 90 degree days in a year is 67 and occurred twice (in 1980 and 2010).

May 2015 was the warmest on record in the Nation’s Capital and was also drier than average.  That changed markedly in June which was the second wettest on record and also the sixth warmest.  Although 3.37” of rain fell during the first nine days of July, only 0.17” has accumulated at National Airport since then.  Last Sunday, July 19, the high temperature reached 98 degrees in the Nation’s Capital making it the hottest day in more than a year.  

After several days with seasonal temperatures and comfortable relative humidity, significant heat and humidity will return this week.  That’s because the area of high pressure that was responsible for the dry and comfortable weather will shift east of the Nation’s Capital.  That will allow warmer, more humid area to ride southerly winds on the backside of the high pressure system into the Mid-Atlantic Region.  

Although a heat wave last month spanned six days, where temperatures exceeded 90 degrees, this week’s heat wave may exceed that total.   Temperatures could also approach the 100 degree mark by the middle of the week in the Nation’s Capital for the first time in more than three years.

Weather Quiz

Tornado in Oklahoma  (Source: NOAA)

True or False.

There has been a significantly higher than average number of tornadoes during the first half of 2015 across the United States.

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Answer to Weather Quiz question from July 8.

C.  106 degrees.   

The hottest temperature on record in the Nation’s Capital occurred twice: on July 20, 1930 and on August 6, 1918.  Ironically, those measurements both came before National Airport opened in 1941.  Since then, weather observations for Washington, D.C. have been made at National Airport.  Baltimore’s hottest temperature on record is 107 degrees.

July in the Nation's Capital

July thunderstorm in Poolesville, MD  (Source: Ashley Adams)

Today’s temperatures are headed toward a seasonal high in the mid to upper 80s across the Mid-Atlantic Region.  That should bring an unofficial end to this week’s heat wave that saw three consecutive days of high temperatures in the 90s.  In fact, Sunday’s high of 98 degrees was the hottest day in the Nation’s Capital in more than a year, since it was 99 degrees on July 2, 2014.  While Monday’s high of 97 degrees was the second hottest temperature so far this year.

It wasn’t just the Nation’s Capital that saw the hottest weather of the summer earlier this week.  Sunday’s high temperature of 97 degrees in Baltimore was its hottest temperature since July 2013 while New York City was 94 degrees on Monday.  According to the National Weather Service, that was the hottest temperature in Central Park since September 2013. 

This week’s weather has symbolized a rather dramatic shift in the month’s weather pattern across the DC Metro Region.  Washington, D.C. averages 3.73” of rain during the entire month of July, so it was quite unusual that 3.37” of rain occurred during the first nine days of the month.  The weather pattern that made June the second wettest on record in the Nation’s Capital continued into July.  However, only 0.17” of rain has fallen since July 9 because of the influence of an area of high pressure.  That’s what brought the Mid-Atlantic Region the sunny and stellar weather for several days last week.

Washington, D.C. averages 36 days of at least 90 degrees in a given year.  So far in 2015 there have been 25 days of at least 90 degrees in the DC Metro Region.  Rain chances are low and temperatures are expected to be near average into the weekend.  Today’s average high in the Nation’s Capital is 89 degrees.  My colleagues and I on the WUSA9 Weather Team will keep you apprised of the latest weather forecast both on-air and online.