2024 hurricane season update

 

Paying attention to the tropics at the shore.

The peak of the Atlantic hurricane season is quickly approaching in mid-September. That's when atmospheric and environmental conditions are the most favorable for tropical storm and hurricane development. Earlier this month NOAA updated its seasonal hurricane forecast to reflect the tropical activity over the first two months of the season (2 tropical storms and 2 hurricanes).

NOAA's updated forecast is similar to its original forecast as it expects a seasonal total of 17-24 tropical storms, of which 8-13 could become hurricanes with 4-7 major hurricanes. An "average" hurricane season sees 14 tropical storms, 7 hurricanes and 4 major hurricanes. The two primary reasons NOAA scientists expect such an active season are abnormally warm ocean water over the tropical Atlantic and the expectation that La Nina conditions will develop.

One of the trademarks of La Nina conditions in the tropical Atlantic is a reduction in the amount of wind shear. Wind shear refers to winds that change in both speed and direction. Less wind shear means conditions are more favorable for tropical development. 

The United States has already had two landfalling hurricanes this season: Beryl and Debby. Beryl set a slew of records while becoming the strongest June hurricane on record in the Atlantic - and first Category 4. It also became the earliest Category 5 in the Atlantic. Fortunately, Beryl weakened considerably before making landfall as a Category 1 in Texas on July 8. Meanwhile, the remnants of Debby brought record rainfall and severe weather to the Mid-Atlantic Region on August 8-9.

While Ernesto made landfall on August 17 as a minimal hurricane, the National Hurricane Center doesn't expect any other tropical storms to develop in the Atlantic over the next few days. However, as recent seasons have shown, things in the tropical Atlantic can ramp up in a hurry. The 2017 Atlantic hurricane season, for example, got markedly more active in late-August, starting with Hurricane Harvey. September 2017 saw four major Atlantic hurricanes, including two Category 5 powerhouses (Irma and Maria). 

The 2020 Atlantic hurricane season had more named tropical storms than any season on record.  It was a back-loaded season with four major hurricanes after October 15. That’s not to say this season will feature similar trends as 2017 or 2020, but atmospheric and environmental conditions are the most conducive for tropical development in September. The next named Atlantic storm this season will be "Francine."

Punishing tropical systems in the Mid-Atlantic Region

 

Hurricane Isabel, September 2003 (Source: NOAA)

As Tropical Storm Debby slowly tracks up the East Coast, it may evoke memories of past tropical systems to impact the DMV.  Here are some of the memorable ones to occur since 2000.

Ida (2021): The DC Metro Area had heavy rain and severe weather due to the remnants of Ida.  A September 1 rainfall record of 4.13” was reported at BWI Airport. Several tornadoes were also reported in the DC Area, including an EF-2 in Anne Arundel County that caused a lot of damage in suburban Annapolis, Maryland. 

Ida ranks as the sixth costliest hurricane in U.S. history with $84.6 billion worth of damage (2024 dollars), according to NOAA. Ida also claimed nearly 100 lives in the United States.

Isaias (2020): It was a minimal Category 1 hurricane when it made landfall in North Carolina on August 3, 2020. However, Isaias had significant impacts in the DMV, including 4 tornadoes in St. Mary’s Co., Maryland. A slew of tornadoes also touched down in central and southern Virginia and on the Eastern Shore. 

Record rainfall also occurred on August 4. along with many downed trees and significant coastal flooding/erosion. Isaias left nearly $6 billion in damage (2024 dollars) with over a dozen fatalities in the United States.

National Airport – 2.48”
Dulles – 1.87”
BWI – 2.32” (its third highest August 4 rainfall total)

Irene (2011): Hurricane Irene made landfall as a Category 1 hurricane on August 27 and brought significant impacts to the Mid-Atlantic Region and the Northeast. A two-day storm total of 3.83” was recorded at National Airport on August 27-28, more than a third of D.C.’s August 2011 rainfall total. August 2011 was D.C.’s rainiest August since 1967, according to NOAA. Irene claimed over three dozen lives and caused $18.8 billion in damage (2024 dollars).

Isabel (2003): Once a Category 5, Isabel weakened to Category 2 intensity before its landfall in North Carolina on September 18. Despite weakening, Isabel caused major flooding and damage across much of the Mid-Atlantic Region and the Northeast. In the D.C. Metro Region, it was responsible for approximately one million power outages. Isabel caused 17 direct fatalities in the United States along with $9.3 billion in damage (2024 dollars).

DC's warm start to August

 

Following DC's fourth hottest July, August has gotten off to a similarly hot start with highs near 100° on August 1 and 2. That's fitting since August is the second hottest month of the year in the nation's capital behind only July. 

Average daily high/low temperatures in Washington, D.C. range from 89°/72° on August 1 to 86°/69° on August 31. D.C.’s hottest August temperature on record was 106° on August 6, 1918, which also tied for D.C.’s hottest overall temperature. Meanwhile, the coolest August temperature of 49° has occurred three times, most recently on August 29, 1986. Weather records in the nation's capital date back to 1871.

On rare occasions, August is the warmest month of the summer. There have been four such instances over the last 20 years, most recently in 2018. Triple-digit heat is also less common in August than in July with none since 2016 in the nation's capital.

August is one of the drier months of the year in Washington, D.C. with NOAA’s updated rainfall average of 3.25”. Three of the last 10 August’s were significantly drier than average with less than 2” of rain (2019, 2015, 2013). In an average year, August is wetter than only four other months (January, February, April and November). Unlike August, those months see essentially no rainfall from decaying tropical systems and rainfall from thunderstorms is also less likely. 

August's warm start will continue in the nation's capital as my colleagues and I on the WUSA9 Weather Team expect more 90s during the upcoming week. NOAA’s Climate Prediction Center expects this month to be a warmer and wetter than average month for the DMV.