What Exactly Is a Hurricane?
An important guide for anyone who lives near the coast
Getting a news alert for a hurricane watch or seeing a massive spiraling storm on your local weather radar can be scary. But when it comes to hurricane preparedness, knowledge is power. With all the weather terms flying around during hurricane season, from tropical storm to hurricane category numbers, it helps to know the exact definition of this dangerous weather event.
Related: 10 Most Disastrous Hurricanes in U.S. History
So what exactly is a hurricane?
A hurricane is a type of cyclone, which is a generic term for any powerful, rotating storm that originates in warm tropical oceans and creates strong winds and heavy rain. Cyclones occur around the world, but are called hurricanes if they occur in the Atlantic and Northern Pacific—so off the coasts of the U.S., Mexico, and in the Caribbean. Elsewhere, they’re called typhoons or tropical cyclones.
A weather system technically becomes a hurricane once it reaches wind speeds of 74 mph (before that, it’s called a tropical storm). From there, hurricanes are broken down into five different categories using the Saffir-Simpson Hurricane Wind Scale.
Hurricanes are made up of the eye (a 20- to 30-mile wide center), the eyewall, and the outer rainbands. The eye is notoriously calm and clear, lacking in winds or precipitation—but you wouldn't want to be caught inside one. Surrounding the eye is the eyewall, a dense, dangerous zone where winds reach their highest speeds. Outside the eyewall, rainbands contain heavy showers that extend hundreds of miles off the center. A typical hurricane spans 300 miles wide, but can grow much bigger (Irma was 425 miles in diameter).
How does a hurricane form?
Hurricanes form over the ocean and usually begin as a tropical wave—and not the fun kind you can splash in. In this definition, tropical waves are areas of low air pressure that move east to west across the tropics.
As the weather system moves westward, warm air rises and incoming air fills that space. That rush of air then rises and cools, forming clouds and thunderstorms. If the cycle continues, the weather system grows and a powerful rotating storm forms.
Now that you know the official definition of a hurricane, be sure to read up on the different categories of hurricanes, the difference between a hurricane watch and warning, and how to board your windows up before a hurricane. When it comes to these powerful weather systems, you can never be too prepared.