One of the biggest sticking points when it comes to weather forecasts is the public's confusion over the terms "hurricane," "typhoon," and "cyclone." Since they're three different names, people think they're three different kinds of storm. Here's a quick explainer on what's in a name.
Aside from slightly different wind speeds, there is no difference between a hurricane, a typhoon, and a cyclone. They are all different names for the same kind of intense low pressure system.
Most people are familiar with two different types of weather systems:
- Low pressure systems, also called "cyclones," spin counter-clockwise in the northern hemisphere
- High pressure systems, also called "anticyclones," spin clockwise in the northern hemisphere.
All low pressure systems are cyclones. There are two different kinds of cyclones that affect the United States most often: tropical cyclones and extratropical cyclones.
A tropical cyclone is a warm-core system that has a warm, humid, tropical airmass throughout the entire storm. Tropical cyclones derive their energy from the intense thunderstorm activity that forms around the eye of the storm. This explainer from Hurricane Bertha's early days gives a little more information on how a tropical cyclone ultimately becomes a tropical cyclone.
An extratropical cyclone, on the other hand, features a process called "temperature advection." Think of cold and warm fronts — extratropical cyclones typically transport warm air from the south and cold air down from the northwest. Extratropical cyclones also gather their energy from the jet stream in a process called "divergence." Air has a tendency to rise rapidly near different parts of the jet stream, and these regions favor the formation and strengthening of extratropical cyclones.
Ideal extratropical cyclones famously look like giant white apostrophes hovering over land. The one pictured above was the "Chiclone" of October 2010, which wound up being one of the most intense extratropical cyclones ever recorded in the United States (its pressure dropped to near 955 millibars).
Now that we've established that all low pressure systems are cyclones, we can look at what different regions of the world call ones that are tropical in nature.
The embarrassingly-bad map above shows the very rough cutoff points for different names. Around North America, we call tropical cyclones "hurricanes." In the western Pacific near Asia, they call tropical cyclones "typhoons." In most of the southern hemisphere and the Indian Ocean, they simply call tropical cyclones a "tropical cyclone."
Keep in mind that a hurricane/typhoon/cyclone generally has winds stronger than 74 MPH. Anything lower than that and it's a buffet of different names. In North America, we call a tropical cyclone with winds less than 39 MPH a "tropical depression." Once the tropical cyclone strengthens and has winds between 39 and 73 MPH, we call it a "tropical storm."
The threshold for naming a system a depression/storm/etc. differs from region to region, but again: same storm, different names.
The dividing line for whether a tropical cyclone is called a hurricane, typhoon, or simply a cyclone is based on latitude and longitude. A perfect example is Hurricane Genevieve. The other day, Hurricane Genevieve crossed the International Date Line (180°W) from American forecasting territory into Japanese forecasting territory. Once it crossed that line, it went from Hurricane Genevieve to Super Typhoon Genevieve simply because it crossed from one region into the other. Same storm, different name.
There are seven official forecasting agencies around the world responsible for issuing forecasts on tropical systems, and each can declare individual storms a hurricane/cyclone/typhoon.
- Americans are most familiar with the National Hurricane Center based out of Miami, which is responsible for hurricanes that form in the northern Atlantic and eastern Pacific east of 140°W longitude.
- If a storm forms in the eastern Pacific and crosses 140°W into the central Pacific, it becomes the responsibility of the Central Pacific Hurricane Center in Honolulu. This agency is responsible for all tropical systems in the northern hemisphere that form between 140°W and the International Date Line (180°W).
- If a storm like Genevieve forms in the CPHC's area of responsibility and moves west over the International Date Line, it becomes the responsibility of Japanese Meteorological Agency, which is responsible for all tropical systems that form in the northwestern Pacific Ocean. They call tropical cyclones "typhoons."
- Around Australia, storms that form are simply called "tropical cyclones" and they're the responsibility of the Australian Bureau of Meteorology.
- In the northern Indian Ocean, tropical cyclones that form are the responsibility of the India Meteorological Department.
- If a tropical cyclone forms in the southwestern Indian Ocean — around Madagascar, for instance — Météo-France is responsible for issuing forecasts.
- Lastly, cyclones that form in the southern Pacific Ocean are under the responsibility of New Zealand's MetService.
In the southern Atlantic Ocean south of the equator, the responsibility for issuing forecasts on tropical cyclones is theoretically no man's land since tropical cyclones are exceedingly rare in the region. In practice, though, the one time a category 2 tropical cyclone hit Brazil in March 2004, Brazilian authorities took forecasting responsibility and named the storm Catarina.
To keep a long story short (ha ha ha!), there is basically no difference between a hurricane, a typhoon, and a tropical cyclone. It's the difference between a tractor trailer and a lorry. The spelling of "harbor" and "harbour." Pronouncing tomato "tomato" or pronouncing tomato "tomato."
Hurricane, typhoon, cyclone. They're all the same type of storm, just called different names.
[Images: NOAA / GOES / NASA / author]