By Max Gallo and Amanda Delaney
The 2024 North Atlantic hurricane season got off to a quick jump in late June with the formation of Alberto, Beryl, and Chris. Meteorologists across the field were in strong agreement that this season would be above average and quite active. Hurricane Beryl shattered records for its strength and early season development. This activity came to a quick halt following Beryl’s dissipation in early July. During July, meteorologists were fascinated by the lack of activity across the basin, with errant tropical waves even becoming hard to find. There are several factors that we are certain have inhibited development during the period.
Sahara Dust
Satellite imagery near the end of June through July showed large plumes of dust blowing off the Sahara Desert and over the region where tropical cyclone development usually occurs off the African coast. The dust is transported by westward moving thunderstorms that track through Western Africa and offshore the coast. This dust is pushed over the Atlantic basin, and if it is strong enough, can reach as far the Gulf of Mexico.
The dust suppresses moisture across the Atlantic Basin which is a key ingredient for tropical cyclone development. While it is typical to have Sahara Dust during this time of year, this particular year the surge in Sahara Dust was the strongest in approximately two years and is likely a significant factor in why the tropical cyclone activity diminished drastically during that time. However, the plumes of dust diminished toward the end of July, which helped allow Hurricane Debby and Hurricane Ernesto to form in the Tropical Atlantic.
The Intertropical Convergence Zone
The Intertropical Convergence Zone (ITCZ) is basically where southeasterly and northeasterly trade winds meet, which forces air to rise, a main ingredient in the genesis of thunderstorms. The ITCZ fluctuates seasonally near the equator early in the year and shifts to the north around June. However, this year the ITCZ was farther south than its mean location during June and was slow to migrate north until closer to the end of July and August this year.
The Madden-Julian Oscillation
One last factor, or rather an absent ingredient, is the Madden-Julian Oscillation (MJO). This is an alternating oscillation of pockets of moist and dry air that travel eastward across the globe along the equator. One typical rotation around the globe takes anywhere between 30 and 60 days. When a dry portion of the MJO is over the Atlantic hurricane basin, an already unfavorable environment becomes even less likely for tropical development. Just like the aforementioned factors, this pocket of dryer air over the region will only last for so long.
Since the end of July though we have had five tropical cyclones that have developed, and it appears the Atlantic basin is making up for lost time. The Sahara dust has disappeared, the ITCZ has shifted back north to where it’s supposed to be, and the Madden Julian Oscillation has drawn moist air back over the Eastern Atlantic Ocean. Therefore we expect that the rest of the Atlantic Tropical Cyclone Season will remain more active than normal until the end of November.
Max Gallo and Amanda Delaney are staff meteorologists at Weather Routing Inc. (https://www.wriwx.com). WRI provides customized forecasts and online weather services to mariners worldwide.
