I had a house full of kids, recently. My son’s friends came over, so that gave us four people under the age of eight running around my house. And as kids do, they talk. One of the children, a seven-year-old girl, was telling everyone else about the tornadoes and recent flooding in Texas. This got them to talking about storms, and soon enough my son stops and asks me a question.
“What’s a hurricane?”
Ah… a big storm? You’d think I would know more. I used to live in Maryland and, while we didn’t get hit with hurricanes the way that (say) Florida did, we still got them coming ashore. I’ve watched the rain hammer down and the wind howl, and then sat in the eye, and then watched the wind and the rain hit again. But it turns out I don’t have a clear idea beyond “a big storm”.
Fortunately, the National Hurricane Center of the National Oceanic and Atmospheric Administration() offers a lot more detail. According to them, a hurricane is one of four varieties of a “tropical cyclone”. A tropical cyclone is, of course, “a rotating, organized system of clouds and thunderstorms that originates over tropical or subtropical waters and has a closed low-level circulation.” These storms rotate counterclockwise in the Northern Hemisphere, and clockwise in the Sourthern Hemisphere. NOAA breaks tropical cyclones into four categories:
- Tropical depression, a cyclone with maximum sustained winds below 39 mph
- Tropical storm, a cyclone with maximum sustained winds of 39 – 73 mph
- Hurricane, a tropical cyclone with maximum sustained winds of 74 – 110 mph
- Major hurricane, a tropical cyclone with maximum sustained winds of 111 mph or more.
Confusingly, hurricanes are known as cyclones in the Indian Ocean and South Pacific Ocean, and as typhoons in the western North Pacific. Tropical cyclones have seasons, with the Atlantic hurricane season running from June 1 through November 30 and the Eastern Pacific hurricane season running from May 15 through November 30.
Intriguingly enough, the winds are not necessarily the most dangerous aspect of a hurricane. Storm surges get that award. These are swells of sea water 30 to 40 miles wide and up to 15 feet higher than the normal tide level that get driven ahead of the storms, acting like a miniature tidal wave when they hit shore.