EYES AND ARMS: THE STRUCTURE OF A HURRICANE
AS THE AIR INSIDE A HURRICANE WARMS UP, much of the air at the surface rises long before it reaches the core. The resulting clouds drop massive amounts of rain. When the air eventually rises high enough to cool, it sinks back to the surface, where it rejoins the inflow and starts the process all over again.
This is called the storm’s secondary circulation, and produces rings of thunderstorms radiating out from the center—rain bands. Though anyone who’s seen a satellite image of a tropical storm can tell you they don’t look like rings. They look like crazy, spiraling arms.
Wind speed isn’t the same throughout the storm; you’ll usually find the highest winds just shy of the center. The reason is that as the spiral tightens inward, the air moves faster (like a spinning figure skater pulling in her arms, the smaller the radius of the spin, the faster the spin). The strange part is that the actual center often has no wind at all—only calm, blue sky.
The eye of a cyclone is calm because winds rushing to the center can’t converge on a point, so they rise, not just up but way up, shooting out of the top of the storm like an invisible volcano. The place where all that sea-warmed air is forced to rise, where it’s wettest and where the air is moving fastest, is called the eyewall. It’s basically a cylindrical, super-destructive wall of clouds, and it’s the part of the storm that does the most damage when it passes over land.