Fluid Mechanics of a Hurricane

Over the Labor Day holiday weekend, Tropical Storm Lee moved across the state of Alabama. This storm caused 2 out of 3 Alabama Power customers to lose power in the Birmingham area. In the wake of this storm I was curious about the fluid mechanics behind tropical storms and hurricanes. To understand how a hurricane works you have to understand the physics at the ocean/air interface. Hurricanes draw their energy from the thermodynamic disequilibrium between the warm tropical ocean waters and the cooler atmospheric air. This disequilibrium causes a low surface-air pressure and a steep pressure gradient that extends out past the eye of the hurricane. This pressure gradient causes winds to sweep from the high pressure areas toward the low pressure center. This low pressure center is measured to be around 900 mb; the lowest case ever measured is 870 mb, which is about 10-15% lower than normal atmospheric pressure.