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AUGUST 28, 2014 -- What does the Sahara Desert in Africa have to do with hurricanes in the Atlantic, Gulf of Mexico, and Eastern Pacific Ocean? You might think this sounds a little crazy because hurricanes are very wet and deserts are very dry, but if it weren't for this huge, hot, dry region in North Africa, we would see far fewer hurricanes in the United States. The Sahara Desert is massive, covering 10 percent of the continent of Africa. It would be the largest desert on Earth, but based strictly on rainfall amounts, the continent of Antarctica qualifies as a desert and is even larger. Still, rainfall in the Sahara is very infrequent; some areas may not get rain for years and the average total rainfall is less than three inches per year. While not the largest or driest of the deserts, the Sahara has a major influence on weather across the Western Hemisphere.
How a Tropical Storm Starts A-Brewin'
The role the Sahara Desert plays in hurricane development is related to the easterly winds (coming from the east) generated from the differences between the hot, dry desert in north Africa and the cooler, wetter, and forested coastal environment directly south and surrounding the Gulf of Guinea in west Africa. The result is a strong area of high altitude winds commonly called the African Easterly Jet. If these winds were constant, we would also experience fewer hurricanes. However, the African Easterly Jet is unstable, resulting in undulations in a north-south direction, often forming a corresponding north to south trough, or wave, that moves westward off the West African Coast. When these waves of air have enough moisture, lift, and instability, they readily form clusters of thunderstorms, sometimes becoming correlated with a center of air circulation. When this happens, a tropical cyclone may form as the areas of disturbed weather move westward across the Atlantic. Throughout most of the year, these waves typically form every two to three days in a region near Cape Verde (due west of Africa), but it is the summer to early fall when conditions can become favorable for tropical cyclone development. Not all hurricanes that form in the Atlantic originate near Cape Verde, but this has been the case for most of the major hurricanes that have impacted the continental United States.
