High waves pound a sea wall in Legazpi, Philippines on November 8, 2013, the day Super Typhoon Haiyan hit the country. Thousands were killed. Image credit: Charism Sayat/AFP/Getty Images
Scientists love standardization. After all, standards are what make it easy to transfer thoughts and data around the world without worrying about language or cultural barriers. But there are certain topics in certain scientific fields where a thirst for uniformity falls by the wayside in favor of regional preferences. This penchant for cultural quirks is no more obvious than when it comes to the storms called "tropical cyclones." It can be confusing to talk about these storms from one region to the next, but it’s really not as daunting as it sounds once you get used it.
1. DESPITE THEIR DIFFERENCES, THEY’RE ALL TROPICAL CYCLONES.
Whenever we talk about “tropical cyclones,” we’re using the scientific term for any low-pressure system that develops over the ocean, contains warm air throughout the storm, and feeds its energy from thunderstorms near the center of circulation. No matter where tropical cyclones form around the world, they all have the same basic features, despite their different names.
2. THERE ARE USUALLY THREE MAIN CATEGORIES …
Hurricane Iselle (center) and Tropical Storm Julio (right) moving toward Hawaii in August 2014. Image credit: NOAA/NASA
Tropical cyclones go through different stages of development on their way to maturity, and each stage is given its own rank. The textbook storm will start as a small batch of thunderstorms surrounding a weak low-pressure center that’s producing sustained winds of around 30 mph. This is typically known as a tropical depression. A tropical depression will turn into a tropical storm as the thunderstorms grow more organized around the spinning low and the winds grow stronger. As a tropical storm strengthens into a hurricane, it’ll look less like a blob of clouds and more like the spiraling storm we’re accustomed to seeing on satellite imagery.
3. … BUT IT’S NOT LIKE THAT EVERYWHERE.
A tropical cyclone advances from one rank to the next based on wind speeds alone. In the Atlantic and eastern Pacific, a tropical depression reaches tropical storm strength when its winds hit 39 mph, and a tropical storm strengthens to a hurricane once its winds reach 74 mph. But different regions of the world will use different wind speed criteria to assign systems different ranks as they mature into powerful storms. A tropical cyclone that forms in the northern Indian Ocean, for instance, skips straight from a tropical depression to a “cyclonic storm” once its winds reach 45 mph, with each step after that qualified with a new intensifier (severe, very severe, and so on).
4. TYPHOONS AND HURRICANES ARE IDENTICAL … MINUS 9 MPH.
North America and Asia seem like the odd ones out when you consider that the rest of the world simply calls a tropical cyclone a “cyclone.” A hurricane is identical to a typhoon—the only difference is that a tropical storm strengthens into a typhoon when its winds reach 83 mph instead of 74 mph as is the case for a hurricane.
The greatest confusion during hurricane season is when a storm forms near Hawaii and people aren’t sure whether to call it a hurricane or a typhoon. A storm that forms near Hawaii is called a hurricane because Hawaii is east of the International Date Line. All strong storms east of this line of longitude are hurricanes. Meanwhile, those that form to the west of the International Date Line are typhoons.
5. SUPERSTORMS DON’T EXIST.
While a "super typhoon" is a typhoon that reaches the equivalent of a category 5 hurricane, as we saw last week with Super Typhoon Meranti, there is no such thing as a “superstorm.” The title is most commonly given to Hurricane Sandy back in 2012. The storm wasn’t technically a hurricane when it made landfall in New Jersey—it had developed cold and warm fronts, and it was producing blizzard conditions in the mountains—yet it still had all the effects of a dangerous and historic hurricane.
Given the system’s unusual nature and impact, reporters started calling it “Superstorm Sandy,” a catchy title that rolls off the tongue and just sounds right when you talk about it. But catchy or not, superstorms don’t actually exist. Sandy was technically a “post-tropical cyclone” at landfall, or a hurricane that transitioned from a tropical cyclone to a common (but powerful) extratropical cyclone. All that means is that it developed fronts and started feeding its energy off of the jet stream rather than thunderstorms fueled by warm ocean waters.
6. WHAT’S IN A NAME, ANYWAY?
Super Typhoon Haiyan approaching the Philippines on November 7, 2013. Image credit: NOAA/NASA
Meteorologists started naming storms in the mid-1900s as a way to easily keep track of them on weather maps and in warnings to the public. Most tropical cyclones will receive a name when they’ve reached the equivalent of tropical storm strength, and the name they receive is based on where in the world they form.
Storms in the Atlantic or eastern Pacific are named by the National Hurricane Center in Miami. They are based on a pre-selected list that alternates male and female names. The same list is used once every six years. The names used for especially bad storms—like Camille and Sandy—are retired and never used again so they don’t cause panic or anguish to those affected by the devastation of the last storm with the same name.
Each ocean basin around the world has different naming conventions. The northwestern Pacific Ocean is so active that they use dozens of names on a continuous loop. Some basins, like the central Pacific around Hawaii, see storms rarely enough that they only have a relative handful of names on tap.
7. WHEN IT COMES TO NAMING STORMS, THE PHILIPPINES GOES ITS OWN WAY.
The list of names each basin uses to keep track of storms is standardized (of course!) and maintained by the United Nations’ World Meteorological Organization. Storm naming before the lists came out was all over the place, and at least one country held on to their past traditions.
Storms in the Philippines receive two names—the international name and the local name assigned by PAGASA, the country’s weather forecasting agency. PAGASA and its predecessor agencies have assigned their own names to storms for decades—even longer than the internationally recognized lists came into existence. Super Typhoon Haiyan, the strongest storm to ever make landfall when it hit the Philippines in 2013 with 190 mph winds, is known in that country by its local name of Typhoon Yolanda. When Meranti recently hit the northernmost islands of the Philippines, local news agencies referred to it by its PAGASA-assigned name of Ferdie.