Hurricanes in May?

 

Tropical Storm Arlene, April 2017 (Source: NOAA)

Hurricane season runs from June 1 through November 30 with the busiest months being August and September. June is typically a quiet month in the tropics, but tropical storms and hurricanes do occur sometimes. Every so often tropical storms also develop before the season officially gets underway.

Although unusual, having a named storm develop before June 1 has occurred more often in recent years. At least one named storm has developed early in the Atlantic a total of nine times since 2012. A system becomes a “tropical storm” and is given a name when the sustained winds around its center reach 39 mph. If sustained winds reach 74 mph, then the tropical storm becomes a hurricane.

On occasion, a named storm has characteristics of both a tropical system and a non-tropical area of low pressure. Under such circumstances, the system is classified as a “subtropical storm.”  That’s what happened with Tropical Storm Alberto in May 2018. It began as a subtropical storm in the Gulf of Mexico. However, it eventually became a fully tropical storm before it made landfall in the Florida panhandle on May 29.

Alberto was also significant for making 2018 one of seven consecutive years at least one named storm formed prior to the official start of the hurricane season. That broke the previous record for most consecutive years that a tropical storm developed prior to June 1 (1951 – 1954).

In January 2016, Hurricane Alex developed south of the Azores and was the first Atlantic hurricane during the month of January since 1955. Some may wonder if having a named storm prior to the official start of hurricane season is a reliable indicator of whether or not a given season will be an active one. Quite simply, it isn’t. If conditions are favorable for a tropical storm to develop prior to June 1, it isn’t a guarantee that conditions will remain favorable for an active hurricane season as a whole.

If a tropical storm or hurricane develops before this June 1, it would be the first season since 2023 that’s occurred in the Atlantic Ocean. The first named storm of 2026 will be given the name “Arthur.”

Summer-like heat in the DMV?

 

NOAA's 6 to 10 day temperature outlook

Washingtonians typically see the first 90-degree temperature of the year on or around May 18. The nation’s capital averages 36 days per year with high temperatures of at least 90° with the majority coming in June, July, and August. Over the last 30 years, the nation’s capital has averaged between one and two 90-degree May days.

Interestingly, Washingtonians haven’t experienced any 90-degree May heat in two of the last three years. However, that has little bearing on how hot the corresponding summer will be. For example, May 2016 was cooler than average in the nation’s capital. No 90-degree heat occurred in 2016 until June 11. However, the summer of 2016 went on to become the third hottest on record (at the time). 

More recently, DC’s first 90-degree day in 2024 was a record-tying high of 91° on May 2. No more 90-degree heat occurred, thereafter, until June 13. Nevertheless, the summer of 2024 finished as DC’s third hottest on record despite the lack of extreme heat in May and the first half of June.

DC’s earliest 90-degree day on record was March 22, 1907 (90°). The latest first 90-degree temperature in the nation’s capital occurred on July 12, 1979 (93°). Both of those summers were significantly cooler than average. This illustrates that no correlation exists between when the first 90-degree temperatures occur and whether a summer is warmer than average.

Washingtonians sometimes experience 90-degree heat before May begins. Such was the case last month when the nation’s capital sweated through its first 90-degree April heat since 2017. Highs reached 90° at National Airport on April 15 and April 16. That was also the first time the nation’s capital experienced two 90-degree April days since 2010.

A “heat wave” is loosely defined as three or more consecutive days in the 90s. The nation’s capital has experienced three of those in May over the last 30 years, with the most recent being in 2019. No triple-digit heat has occurred in the nation’s capital in May, but highs reach 95° roughly once every five years with the most recent on May 31, 2022 (96°).

NOAA’s Climate Prediction Center expects a hard pivot to more summer-like weather in the nation’s capital next week, following a near to cooler than average week.

May’s uptick in severe weather

 

Hail from southern Maryland (Photo Credit: Kristen Leitch)

May is one of the most active severe weather months of the year in the United States. NOAA defines “severe weather” as a thunderstorm that produces any of the following: A) wind gusts of at least 58 mph; B) hail 1” in diameter or greater; or C) a tornado. 

The most dangerous thunderstorms (supercells) can cause more than one type of severe weather as large hail often precedes tornadoes. The area in and around the nation’s capital has had a number of memorable May severe weather events.   

2019: Three tornadoes touched down in central Maryland on May 30, producing two EF-0’s and an EF-1 in Frederick and Howard Counties. Wind damage was more widespread across the DC Metropolitan Area, with a wind gust as high as 71 mph in Frederick County, Maryland. A 66 mph wind gust was also reported at Davison Army Airfield in Fairfax County, Virginia. 

Even more severe weather impacted the DMV (DC, Maryland and Virginia) just a week earlier. An EF-1 tornado was confirmed in Columbia, Maryland that caused some structural damage. There were also many severe wind gusts from the thunderstorms that developed. Winds gusted as high as 68 mph at National Airport, 63 mph at Andrews AFB in Maryland, and 67 mph in Gaithersburg, Maryland. Damage was reported that ranged from downed trees and power lines to minor structural damage of homes and businesses.

2016: On May 2, hail 2.5” – 2.75” in diameter, ranging in size from tennis ball to baseball, occurred in Rockville, Maryland. Baseball-size hail was also reported in Charles County, Maryland, while golf ball-size hail was seen in Huntingtown. There were other reports of hail in the DMV that were smaller, but still met severe criteria.

2008: Several tornadoes developed in north-central Virginia on May 8. A weak tornado also developed in Camp Springs, Maryland. The strongest tornado in the DMV during this outbreak was an EF-2 in Stafford County, Virginia with peak winds of 120 mph. Many severe wind and hail events were also observed in Maryland and Virginia.

2002:  An F1 tornado was confirmed in Rockville, Maryland on May 13. It was part of a larger outbreak that saw a number of severe wind and hail reports. There was an F2 tornado on May 2 north of Baltimore in Cecil County, Maryland with winds of 150 mph. A weaker tornado was also reported in Rockville, Maryland. There were also multiple reports of severe wind gusts and hail.