How Hot Can It Get ?

As DC’s third hottest month of the year, Washingtonians have seen their fair share of June heat and humidity.  Today is quite tropical with highs this afternoon on the way to being around 90° combined with dewpoint temperatures in the low to mid 70s that will produce a heat index or “feels-like” temperature near 100°.  While uncomfortable and dangerous, today’s highs aren’t near record levels.

DC’s record highs during the month of June are 100°/+ on 12 different days, while they are at least 95° the rest of the month.  While triple-digit heat is relatively uncommon in the Nation’s Capital in June, it has happened 10 times since National Airport opened during World War II.  The most recent incidence of triple-digit heat during June was June 29, 2012 when DC’s record June temperature of 104° was observed.  

The month of June has been quite hot in the DC Metro Area over the last decade, with the last cooler than average June in 2009.  Six of DC’s 10 warmest June’s have occurred just since 2010.  June has actually been hotter than the month of August in the Nation’s Capital five times since 1980.

July is DC’s hottest month of the year overall based on average temperature.  Of July’s 31 days, 28 have record highs of 100° or higher.  DC’s most recent triple digit heat in July occurred on July 25, 2016.  The record for most 100° July days in Washington, D.C. is seven that occurred in 2012.  Eight of DC’s 20 hottest July’s have occurred just since 2010.

August is DC’s second hottest month of the year.  Nineteen of DC’s 31 daily record highs during the month of August are 100°/+.  The most recent triple-digit August heat in the Nation’s Capital was in 2016.  Five of DC’s 10 hottest Augusts have occurred just since 2002.  August has been DC’s hottest month of the year eight times since 2000, most recently in 2018.

Having one really hot summer month doesn’t necessarily mean the entire summer will be extremely hot.  For example, although June 1994 was one of DC’s hottest on record with a 14-day heat wave and July 1994 was also hotter than average, August 1994 finished more than 2° cooler than average.  Conversely, while June 2016 had only five days of 90° in the Nation’s Capital, the 2016 summer finished as one of DC’s hottest on record.  Fortunately for those who don’t care for extreme heat or humidity, my colleagues and I on the WUSA9 weather team don’t have any 90s on the seven-day forecast after today.

Weather Quiz

True or False. 

The month of June is typically the third hottest month of the year in the Nation’s Capital.

If it’s June, it must be Hurricane Season !

Hurricane Alex Making Landfall in 2010  (Source: NOAA)

Although hurricane season officially gets underway June 1, there are typically very few hurricanes during the month of June.  That’s because environmental conditions don’t often become favorable over a large area until later in the season.  However, there have been some significant June hurricanes.

2012: The most recent June hurricane in the Atlantic was named Chris.  At peak intensity, Chris was a minimal Category 1 hurricane with 85 mph and didn’t make landfall.  It developed in the northern Atlantic, where sea surface temperatures were in the mid-70s – below the typical threshold of 80° that tropical systems need for intensification.

2010: Alex was a Category 2 at peak intensity with sustained winds of 110 mph when it made landfall in Mexico.  Its minimum central air pressure fell to a low 946 millibars (mb), which is more commonly found in a strong Category 3 or a Category 4 hurricane.  Air pressure often falls more quickly in an intensifying tropical system than wind speeds can increase.  That’s why scientists use air pressure instead of wind speed as a more accurate measure of tropical cyclone intensity. 

Alex was also the Atlantic’s first June hurricane since Allison in 1995.  Its minimum air pressure of 946 mb also tied it with 1957’s Hurricane Audrey for lowest pressure in an Atlantic hurricane during the month of June.

1986: The name “Bonnie” was first used in 1980 and has been a named storm seven times since then.  In 1986, Bonnie developed in late June and became the first hurricane of the season.  It made landfall along the eastern Texas coast on June 25 as a Category 1 with sustained winds of 85 mph.  This was the last time a June hurricane made landfall in the United States.

1968: June was active in the tropical Atlantic with three named storms, including two hurricanes.  Abby was a minimal Category 1 with peak winds of 75 mph, but weakened to a tropical storm before making its initial landfall near Punta Gorda, Florida on June 4.  It made a second landfall as a weaker storm near Jacksonville, Florida. 

Later in the month another tropical depression impacted the state of Florida.  However, it wasn’t named Tropical Storm “Brenda” until after it had moved eastward into the Atlantic and away from Florida.  Brenda became a Category 1 storm with peak winds of 75 mph before it dissipated over the open Atlantic. 

1966:  Hurricane Alma was an exceedingly rare major hurricane that developed in June.  At peak intensity in the Gulf of Mexico on June 8, it was a Category 3 storm with sustained winds of 125 mph.  Fortunately, it weakened to a Category 1 storm before making landfall near Apalachee Bay, Florida on June 9.  Alma remains the last major hurricane to develop anywhere in the Atlantic Ocean during the month of June.

The Unofficial Start of Summer

NOAA's Temperature Outlook for June 2020

Although astronomical summer doesn’t get underway until the summer solstice later this month, meteorological summer began yesterday.  “Meteorological summer” runs from June 1 through August 31.  Following a cooler than average April and May in the Nation’s Capital, many are eager for warmer weather.  They’ll get their wish as high temperatures will reach 90°/+ for the first time of the year tomorrow.

Average temperatures rise in the Nation’s Capital throughout the month of June from a high/low of 80°/62° on June 1 to 88°/70° by the end of the month.  June has the third highest average monthly temperature (combining daily high/low temperatures) of the year in the DC Metro area, behind only July and August.  Since 2000, 14 of the last 20 June’s have been warmer than average in Washington, D.C., including the last 10.  DC’s hottest June temperature on record of 104° occurred relatively recently on June 29, 2012.  By comparison, DC’s coolest June temperature of 43° occurred more than 120 years ago on June 2, 1897.  Meanwhile, the earliest Washingtonians have experienced triple-digit heat was when it reached 100° on June 5, 1925.

June has been a rainy month more often than not over the last two decades with 13 of the last 20 being wetter than average.  That’s saying something since June is DC’s second wettest month of the year, with a rainfall average of 3.73”, behind only May’s 3.99”.  Several of DC’s 10 wettest June’s have also been warmer than average.  Such was the case in 2013 and 2015.  Both years ranked among DC’s Top 5 rainiest, while being warmer than average.  June 2015 also happened to be DC’s sixth warmest June. 

It’s also significant that six of DC’s 10 warmest June’s have occurred since 2008, while three of DC’s wettest June’s have occurred since 2006.  Although rare, the DC Metro Area can feel the impacts of decaying tropical systems.  Longtime Washingtonians may remember the record flooding of June 1972 from the remnants of Hurricane Agnes.  That was DC’s wettest June until 2006 and has since fallen to third place. 

Another key trend in the DC’s Metro Area has been the disproportionate number of record highs in recent decades compared to record lows.  For example, the month of June has had 11 record highs in the last 20 years.  Meanwhile, you have to all the way back to June 22, 1992, for the last time the Nation’s Capital experienced a record low temperature.  A key reason for that has been the increasing amount of urbanization and automobile traffic that’s enhanced the urban heat island effect.  NOAA expects June 2020 to again be warmer and drier than average.