The Anatomy of a Hurricane

All Tropical Cyclones are Made Up of an Eye, Eyewall, and Rainbands

Given a satellite image, you could probably spot a tropical storm faster than you can say "hurricane hunters." But would you feel as comfortable if asked to point out the storms' three basic features? This article explore each, starting at the heart of the storm and working outward to its fringes.

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The Eye (The Storm Center)

Satellite image highlighting Hurricane Wilma's (2005) eye. Wikimedia Commons

At the center of every tropical cyclone is a 20 to 40 mile-wide (30-65 km) doughnut-shaped hole known as the "eye." It's one of a hurricane's most easily recognizable features, not only because it's located at the geometric center of the storm, but also because it's a mostly cloud-free area—the only one you'll spot inside the storm. 

The weather within the eye region is relatively calm. They are also where the storm's minimum central pressure is found. (Tropical storms and hurricanes are strength is measured by how low the pressure is.)

Just like human eyes are said to be a window to the soul, hurricane eyes can be thought of as a window to their strength; the more well-defined the eye looks, the stronger the storm is. (Weak tropical cyclones often have lop-sided eyes, while infant storms like invests and depressions are still fledgling disorganized they won't even have an eye yet.)

 

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The Eyewall (The Roughest Region)

Visible satellite image highlighting Hurricane Rita's (2005) eyewall. NOAA

The eye is wreathed by a ring of towering cumulonimbus thunderstorms known as the "eyewall." This is the most intense part of the storm and the region where the storm's highest surface winds are found. You'll want to remember this if a hurricane ever makes landfall near your city, since you'll have to endure the eyewall not once, but twice: once when the front half of the cyclone impacts your area, then again just before the back half passes over.

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Rainbands (The Outer Region)

Visible satellite image highlighting a hurricane's spiral rainbands. NOAA

While the eye and eyewall are the nucleus of a tropical cyclone, the bulk of the storm lies outside of its center and is comprised of curved bands of clouds and thunderstorms called "rainbands." Spiraling inward toward the storm's center, these bands produce heavy bursts of rain and wind. If you started at the eyewall and traveled toward the storm's outer edges, you'd pass from intense rain and wind, to less heavy rainfall and lighter winds, and so on and so forth, with each period of rainfall and wind becoming less intense and shorter in duration until you end with light rain and a weak breeze. When traveling from one rainband to the next, windless and rainless gaps are typically found in-between.

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Winds (Overall Storm Size)

sandyswath2012
At 945 miles (1520 km) in diameter, hurricane sandy (2012) is the largest Atlantic hurricane on record. NOAA/NASA

While winds aren't a part of a hurricane's structure, per se, they are included here because they're directly related to a very important part of storm structure: storm size. However wide across the wind field measures (in other words, its diameter) is taken to be the size.

On average, tropical cyclones span a swath of a few hundred miles (which means their winds extend outward this far from their center). The average hurricane measures roughly 100 miles (161 km) across, whereas tropical-storm-force winds occur over a greater area; in general, extending out as far as 300 miles (500 km) from the eye.