Multiple research groups predict that the 2024 hurricane season will be very active; that is, “above normal,” with as many as 25 named storms, 13 hurricanes, and 7 major hurricanes (Category 3 or above) in the Atlantic Ocean.
Last month, in its midseason update, the Climate Prediction Center's forecast changed little: 17 to 24 named storms, 8 to 13 hurricanes and 4 to 7 major hurricanes. However, we are at the peak of the season with only six named storms.
Climate conditions are changing and two disturbances have occurred in the Atlantic Ocean, but the lull has left many feeling misled by the forecasts.
This season we have the opportunity to observe an extraordinary and rare phenomenon: rain in the Sahara Desert. This event allows us to have fewer cyclonic systems at this stage of the season than expected so far. This does not mean that this prediction cannot be realized, although we hope not, because the goal of meteorologists when making predictions is not to make it happen, but to prepare us to be able to mitigate the effects of these phenomena.
In a previous article, I explained that the high heat capacity of water allows it to accumulate heat for a longer period of time than other substances, so the accumulated energy index of the ocean is high and certain phenomena are possible. This is especially true outside of the season, that is, when the water releases all its accumulated energy in the form of heat.
intertropical convergence zone
The northward shift of the Intertropical Convergence Zone has profound consequences for global climate patterns, particularly in the Northern Hemisphere. This area is a band of clouds, rain, and storms that runs along the Earth's equator. It forms when trade winds from both hemispheres converge, causing air containing moisture to move upward, causing clouds and rain.
Typically, this zone is located between 5° north and 5° south latitude, but in summer it can move above 10° north latitude, which produces unusual rainfall events in traditionally arid regions such as the Sahara Desert.
The northward movement of the Intertropical Convergence Zone results in increased rainfall in the Sahara, including its southernmost drier region, the Sahel. Although infrequent, these rainfalls have a considerable impact because they cool the region, limiting the formation of tropical waves that normally produce tropical cyclones.
Saharan dust is also affected
Additionally, increased precipitation in the region affects the transport of Saharan dust to the Caribbean. On either side of the region, Hadley cells form a high-pressure system that stabilizes the atmosphere and contributes to the creation of large desert areas. These cells are part of the general circulation of the atmosphere and are vital to maintaining atmospheric balance, but any change in the position of the Intertropical Convergence Zone could severely impact these cells.
Climate experts are observing and analyzing the long-term consequences of the region's continued northward shift. Such changes could alter global climate patterns, affecting the frequency and intensity of extreme weather events such as cyclones and droughts in normally humid regions, with unpredictable impacts on agriculture, water supplies and ecosystems around the world.
The black line in the figure shows the normal behavior of the Intertropical Convergence Zone. The blue line shows this year's behavior. The displacement began in mid-May.
The Sahara was not always a desert
To clarify, the Sahara is not always a hot desert. 5,000 to 10,000 years ago, this was a green area with dense lakes and rivers and lush vegetation. But changes in Earth's orbit caused changes in Earth's weather patterns, suddenly turning this green area into one of dry desert territory. As shown, these climate changes always take thousands of years, but this weather pattern may be accelerating due to global warming.
The region experienced periodic wet periods during the Quaternary and beyond. But the last rainfall of similar intensity was in 1944.
NOAA's latest analysis of the Intertropical Convergence Zone shows that it has moved much further north.
This means that when this situation returns to normal, tropical disturbances will become active again in areas off the coast of Africa, including the Cape Verde region, and therefore, the number of tropical cyclones in our region will increase. We're already seeing this with the tropical depressions and disturbances in the Atlantic Ocean right now.
