What stands out about DC's May weather?

 

A May day in suburban Washington, D.C.

May 2024 has been a memorable weather month in the nation's capital with 20 days of rain. Despite the frequent rainfall, it will also finish as a warmer than average month for only the second time in the last five years. 

The nation's capital had 4.30" of May rainfall as of May 30, making this a wetter than average May. While there have been a lot of rainy days, there has been very little heavy rain. That's unlike May 2018 that featured four days of at least an inch of rain and finished as DC's sixth wettest May with 8.73". By comparison, DC's rainiest day this month occurred on May 4 with 0.82".

Temperatures this month have been rather in the nation's capital. Seven of the first nine May days were warmer than average and that was followed by seven cooler than average days through May 18. However, this month will finish on a warmer than average note with above average temperatures from May 19 through May 28. 

Although DC saw its first 90-degree day of 2024 on May 2 with a high of 91°, no record warmth occurred downtown. Meanwhile, Dulles Airport saw a record high of 91° on both May 2 and May 22. DC's average monthly temperature finished at 69.3°. That's more than 2° above average and means May 2024 ranks among DC's Top 20 warmest May's.

1. 73.2° (2015)
2. 73.0° (1991)
3. 72.4° (2018)
4. 71.8° (2004)
5. 71.6° (1944)
6. 71.4° (2012)
7. 71.0° (2019)
8. 70.5° (1880)
9. 70.1° (1953)
10. 70.0° (1911)
11. 69.8° (1959)
12. 69.7° (1975)
13. 69.6° (1918)
14. 69.5° (1980)
15. 69.4° (2010, 1977)
17. 69.3° (2024)
Average: 67.2°

Weather Quiz

 

Great Falls, Maryland

True or False.

How warm and wet or cool and dry May could be in the nation's capital has no bearing on how hot the summer months may be.

All signs are for an active 2024 Atlantic hurricane season

 

Hurricane Idalia near Florida, Hurricane Franklin in the Atlantic, 8-29-23 (Source: NOAA)

NOAA has issued its May hurricane forecast for the Atlantic Ocean. It calls for a seasonal 2024 total of 17 to 25 tropical storms (sustained winds of at least 39 mph), of which 8 to 13 intensify into hurricanes (sustained winds of at least 74 mph), with 4 to 7 of those becoming "major" hurricanes (Category 3 or higher with sustained winds of at least 111 mph).  This is the most tropical cyclones they have ever forecast for a given Atlantic hurricane season in the 25 years they have been issuing them. 

NOAA scientists have a 70% confidence in these forecast totals and also predict an 85% chance for an above average Atlantic hurricane season.  That is the highest degree of confidence NOAA has had in one of its forecasts for an above average hurricane season.  An "average" hurricane season features 14 tropical storms, 7 hurricanes and 3 major hurricanes.  NOAA's forecast is similar to the Colorado State forecast that calls for 23 tropical storms, of which 11 becomes hurricanes, with 5 major hurricanes. 

Both NOAA and CSU cite the same two primary conditions in their respective forecasts.  Following one of the strongest episodes of El Nino in recent memory, La Nina conditions are expected to quickly develop this summer.  Earlier this month, NOAA's Climate Prediction Center issued a "La Nina Watch" with a 49% chance La Nina conditions will develop by August 31.  It also indicated a 69% chance La Nina conditions will develop by the September peak of the Atlantic hurricane season. 

La Nina conditions correlate to above average sea surface temperatures in the tropical Atlantic with below average levels of wind shear.  Wind shear are winds that differ in speed or direction with altitude. The absence of wind shear allows for tropical storms and hurricanes to develop and intensify more freely.

Hurricanes typically require warm ocean water of sufficient depth, commonly at least 80° Fahrenheit to a depth of 200’, to develop.  Regardless of the anticipated development of La Nina conditions over the summer, sea surface temperatures are already as warm as they normally are in August in the "MDR" or "Main Development Region" of the Atlantic Ocean. The combination of unusually warm ocean water with a lack of wind shear creates an ideal environment for tropical storm and hurricane development.

However, the overall number of tropical storms and hurricanes that develop 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.  It was the costliest natural disaster in U.S. history at the time and remains one of the costliest hurricanes on record.  On the other hand, 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 2024 Atlantic hurricane season officially gets underway on June 1.  The first named storm of the season will be "Alberto."