Memorable May heat waves

 

A warm day in the nation's capital

Last week the nation’s capital had its first May heat wave in seven years. A “heat wave” is loosely defined as three or more consecutive 90-degree days. Although the nation’s capital has averaged between one and two 90-degree May days over the last 30 years according to NOAA data, late-spring heat waves are relatively rare.

2026: DC residents sweat through July-like heat from May 18 – May 20 with record heat at all three local airports. DC’s average daily high/low temperatures during this heat wave were 95.3°/70°. DC’s high of 97° on May 19 was DC’s hottest May temperature since 2011.

2019: Washingtonians experienced an unusual May heat wave from May 28 – May 30. The hottest of the three days was May 29 with high/low temperatures of 93°/74° at National Airport. No record heat occurred downtown during this stretch, but Dulles Airport had a record-tying high of 90° on May 28. DC’s average high/low temperatures for this three-day period were 91.3°/72°.

2018: This heat wave stood out not for being record-setting, but for occurring early in the month. DC’s average high/low temperatures for the heat wave from May 2 – May 4 were 90.3°/63°. May 2018 remains DC’s third warmest on record.

2013: DC’s first May heat wave in 17 years occurred from May 29 – May 31. Again, this heat wave wasn’t memorable for featuring record-setting heat, but rather for being DC’s first May heat wave of the century. DC’s average daily high/low temperatures for this modest heat wave were 90.3°/69.7°.

1996: DC’s final heat wave of last century occurred from May 19 – May 21. A record high of 96° occurred on May 20 that was ironically eclipsed last week.

It’s important to note that while the nation’s capital typically sees its first 90-degree day of the year on or around May 18, such heat is uncommon this month. Very hot May days do sometimes occur in the nation's capital without there being an official heat wave. Such was the case, for example, on May 31, 2022, when a high of 96° occurred at National Airport. DC's hottest May temperature on record was 99° on May 31, 1991. 

Below average hurricane season is likely

 

Photo Credit: NOAA

NOAA says there is a 55% chance the 2026 Atlantic hurricane season will be have below-normal level of activity. 

The May hurricane forecast from NOAA is for a seasonal total of 8 to 14 tropical storms (sustained winds of at least 39 mph), of which 3 to 6 intensify into hurricanes (sustained winds of at least 74 mph), with 1 to 3 of those becoming "major" hurricanes (Category 3 or higher with sustained winds of at least 111 mph). The seasonal average is for 14 tropical storms, 7 hurricanes and 3 major hurricanes. 

NOAA's forecast is similar to the Colorado State University forecast that calls for 13 tropical storms, of which 6 becomes hurricanes, with 2 major hurricanes. Both NOAA and CSU cite the same two primary conditions in their respective forecasts. 

NOAA’s Climate Prediction Center said in a May 14 update that an 82% chance exists for an episode El Nino to develop by the end of July. El Nino conditions correlate to a higher amounts of wind shear in the tropical Atlantic. Wind shear are winds that differ in speed or direction with altitude. Sea surface temperatures also tend to be cooler in the tropical Atlantic during an El Nino event.

Also, hurricanes typically require warm ocean water of sufficient depth to develop, commonly at least 80° Fahrenheit to a depth of 200’. Currently, sea surface temperatures are slightly warmer than average in the “MDR” or "Main Development Region" of the Atlantic Ocean. However, that’s down significantly from the record warm water temperatures that existed in this part of the Atlantic in 2024. If 2026 is a below average season, then it would be only the second below average season this decade.

Regardless of how many named storms develop, the overall number of tropical storms and hurricanes is less important than where they track. An otherwise quiet season could be very destructive and deadly. For example, the 1992 Atlantic season was relatively quiet with only 7 tropical storms, 4 hurricanes and 1 major hurricane. But that major hurricane was Andrew, which made landfall in southern Florida as a rare Category 5 storm. Andrew was the costliest natural disaster in U.S. history at the time and remains one of the costliest hurricanes on record. Meanwhile, the 2010 season was an active one with 19 tropical storms, 12 hurricanes and 5 major hurricanes, but with no significant impacts in the United States.

The 2026 Atlantic hurricane season officially gets underway on June 1. The first named storm of the season will be “Arthur.”

Weather Quiz

 

The White House, Washington, D.C.

Prior to this week’s heat wave, when was the last time the nation’s capital experienced a May heat wave?  A “heat wave” is loosely defined as three or more consecutive 90-degree days.

A. 2019

B. 2013

C. 1996

D. 1991

DC’s worsening drought conditions

 

NOAA's precipitation outlook

Severe drought conditions now cover the entire DC Metro Area and the record heat this week has only made conditions worse. The rain and showers in the forecast over the coming days are beneficial despite the bad timing ahead of the Memorial Day holiday weekend.

Chronic drought conditions of varying intensity have been an ongoing issue for much of the DMV (DC, Maryland and Virginia) the last ten years. That’s because 21 of the last 32 months have been drier than average in the nation’s capital dating back to September 2023, including nine of the last 12 months with below average rainfall. This drier than average 32-month period has led to an accrued rainfall deficit of 12.71” in the nation’s capital as of April 30.

Although today will be the third and final day of record heat across the DMV, this May has been cooler than average, overall, in the nation’s capital. Cooler than average temperatures starting tomorrow combined with increased rainfall chances over the next several days are a positive development. While not enough rain will occur the next few days to make up DC’s entire deficit, it will help May finish with near average monthly rainfall.

The current 32-month stretch of drier than average weather is similar to another such period of even drier conditions. The nation’s capital had 25 drier than average months in the 32-month period from August 2015 – March 2018. That produced a rainfall deficit of 16.42”. Widespread moderate to severe drought conditions enveloped much of the DMV as of mid-February 2018. A hard pivot in the weather pattern then occurred and 2018 ended up being DC’s wettest year on record.

A similar degree of hope also exists now. Not for record rainfall, but a recent outlook issued by NOAA’s Climate Prediction Center shows an expectation for above average rainfall potential through mid-July across the DMV. That would be great news after such a prolonged stretch of drier than average weather.