A tropical cyclone is an iconic storm that strikes fear (or laughter) in the heart of coastal residents around the world. Most of these low pressure systems over the ocean are weak, but some can grow into monsters. If they’re all the same kind of storm, though, why do we call them different names around the world?
We know them here in the United States as hurricanes. The official name for this meteorological phenomenon is a tropical cyclone, as opposed to an “extratropical cyclone” like the ones we commonly experience over land as a result of the jet stream.
A tropical cyclone is a warm-core low pressure system (warm and muggy air from the surface to the top of the atmosphere) with deep thunderstorm activity that surrounds a closed circulation of winds at the surface. Tropical cyclones feed their energy off of the warm water beneath them, accumulating strength through the thunderstorms surrounding the eye of the storm (the eyewall).
As the updrafts that feed these thunderstorms grow stronger, they suck more air away from the surface, creating lower air pressure at the center of the tropical cyclone. The resulting pressure gradient creates violent winds at the surface as air tries to rush toward the low pressure minimum to fill it back up.
Believe it or not, there is a reason that tropical cyclones exist! Weather is the result of the atmosphere trying to smooth out the extremes and balance itself out; these cyclones exist as a way for the atmosphere to transfer heat from the tropics to the poles, a futile attempt to balance the two out by way of total and complete devastation.
What’s in a Name?
No matter where a tropical cyclone develops—whether it’s near Florida or Japan or Australia or even Brazil—a tropical cyclone is still a tropical cyclone. They form from the same processes in similar environments, and aside from slightly different wind speed requirements, a hurricane, a typhoon, and a cyclone are all the same thing.
When a tropical cyclone becomes well organized and produces damaging winds greater than a certain level (usually around 74 MPH), it’s considered “mature.” Hurricanes, typhoons, and cyclones are all classifications that represent the mature stage of a tropical cyclone. Lesser-organized and weaker cyclones (immature, I guess?) are universally called tropical storms and tropical depressions, though each ocean basin has vastly different wind requirements for each of these lesser classifications.
We call them hurricanes around North America because of the heavy Spanish influence on the continent in the 15th and 16th centuries—the Spanish word for hurricane is huracán. “Typhoon” entered the English language when explorers interacted with residents of southwest and southern Asia—according to the Online Etymology Dictionary (which probably isn’t wrong), the word comes from tufan, which means “big cyclonic storm” in Arabic, Persian, and Hindi.
The reason different regions call the same storm a “hurricane” or “typhoon” is the same reason your weird, old relative from Wiscahnsin is upset the office bubbler isn’t working. The shoes you wear to gym class, for instance, are called tennis shoes, gym shoes, sneakers, athletic shoes, or running shoes depending on where you are in the United States. Except, instead of putting on your sneakers to play tennis, you’re boarding up your house and fleeing inland.
How do you determine the cutoff line between a hurricane and typhoon, though? Tropical cyclone tracking around the world is broken down into different ocean basins. We track tropical cyclones in the Atlantic Ocean separately from those that form in the eastern Pacific or southwestern Pacific near Australia.
Each ocean basin is covered by a different meteorological organization responsible for issuing forecasts in that region of the world. The National Hurricane Center down in Miami covers tropical cyclones that form in the North Atlantic (from the Equator to the Arctic, including the Gulf of Mexico and Caribbean) and eastern Pacific. The Central Pacific Hurricane Center in Honolulu covers tropical cyclones that form in the central Pacific Ocean, which is an area between the International Date Line (180°W) and 140°W. The list goes on for other regions.
Other than figuring out when tropical cyclone season starts and stops, as well as determining forecast jurisdiction, ocean basins are most important when determining what to call these systems.
A mature tropical cyclone (winds of 74+ MPH) that exists east of the International Date Line (180°W) and north of the Equator—an area covering the central and eastern Pacific Ocean—is a hurricane. I get bombarded with emails about this every time I write about a storm on the other side of North America—“uh, actually, you’re supposed to call them typhoons, sir”—but trust me, a mature tropical cyclone near Hawaii or Mexico is called a hurricane.
A mature tropical cyclone west of the International Date Line (180°W) and north of the Equator is a typhoon. A tropical cyclone turns into a typhoon in the western Pacific—near Asia—when it has winds of 74 MPH or greater. Guam and the Northern Marianas Islands are west of the International Date Line.
This brings up a strange issue—what about storms that cross the International Date Line? Well, we had an example of that today. Hawaii was briefly worried that a storm named Tropical Storm Kilo could threaten the islands, but it drifted west instead, quickly becoming a category four hurricane this past weekend. Hurricane Kilo kept moving west, and farther west, and even farther west until it eventually crossed the International Date Line. Once Hurricane Kilo crossed the other side of 180°W, it became Typhoon Kilo. Same storm, same winds, same everything, just a different name.
The southern hemisphere makes things easy for us. Every mature tropical cyclone in the southern hemisphere (and the Indian Ocean) is simply called a “cyclone.” Phailin, a destructive storm that made landfall on India’s east coast back in 2013 with winds of more than 100 MPH, was called Cyclone Phailin.
Tropical cyclones rarely form in the southern Atlantic, but there too they’re called cyclones, and the southern Pacific Ocean near South America is far too cold and hostile to support any sort of tropical development. If one ever formed in this part of the world, though, it would probably be called a cyclone instead of a hurricane or typhoon.
Our classifications schemes are a bit hard to keep up with, but it’s pretty easy to remember what to call each storm. If a strong storm threatens the United States or Caribbean, it’s a hurricane. If a strong storm is aiming for Asia, it’s a typhoon. Everywhere else, it’s just called a cyclone.
[Top Image: Typhoon Nabi in the western Pacific, September 2005, via NASA | Animated Satellite: Super Typhoon Haiyan making landfall in the Philippines, November 2013, via NOAA | Maps: author]