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Hurricane Fay was a resounding disappointment/relief , but it does give us occasion to answer some why-s about hurricanes.  

Why does every hurricane seem to form off the coast of Africa, travel west and then fly up the Gulf of Mexico? It starts with the Bermuda High, a big clockwise-turning wheel of high pressure (dense, cold air that has sunk low in the atmosphere). It’s known as an anticyclone because it rotates in the opposite direction of hurricanes (low-pressure systems.) The Bermuda High forms in the summer and usually remains stationary throughout hurricane season. The closer it forms to the U.S., the higher our risk. What the Bermuda High does is fling low-pressure systems (potential hurricanes) westward, along the African easterly jet, one of few North American wind streams that move east-west.

The storms’ northward motion over Cuba and the Keys can be attributed in part to the Coriolis force. I.e., an object moving across a rotating surface will appear, when viewed by another object (you or me) on that same surface, to bend in its path. Let this handy gif explain it better than my clumsy prose.In the northern (southern) hemisphere, the Coriolis force sends winds to the right (left) of their direction of motion. That means a storm moving to the west will veer north. 

This effect also explains the very existence of hurricanes. Winds are a function of a simple law of physics: fluids move from areas of high pressure, high density to regions of low pressure, low density, as they try to achieve equilibrium. When an area of low pressure forms in the Atlantic Ocean, the surrounding air wants to rush in and fill the space. All else being equal, the air should find equilibrium rather quickly and calm down.

But alas, the winds are sent off course before they can reach their destination. The culprit is, you guessed it, the Coriolis force. All the winds trying to find the storm’s center are sent off to the right. As this happens on all sides, the result is counterclockwise motion. In the southern hemisphere, where moving fluids veer left, the result is clockwise motion. So in a way, hurricanes are spinning, frustrated failures, spreading destruction until they burn out somewhere in Florida.  

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