How Are Hurricane Categories Determined?

Satellite photo of Hurricane Dorian, a Category 5 storm, tracks toward the Florida coast on September 1, 2019.
Satellite photo of Hurricane Dorian, a Category 5 storm, tracks toward the Florida coast on September 1, 2019.
NOAA via Getty Images

Residents of the Bahamas are in the midst of Hurricane Dorian, a Category 5 storm that prime minister Hubert Minnis said has already caused "unprecedented" devastation to the area. Meanwhile, residents of Florida, Georgia, and the Carolinas are being evacuated ahead of the storm's potential arrival in the U.S. At this point, we've become accustomed to hearing about hurricanes, and to predicting what sort of damage they might cause based on their category number. But how do meteorologists categorize these often-deadly storms, and how does that scale work?

First, a quick primer: Hurricanes are tropical cyclones that occur in the Atlantic Ocean and have winds with a sustained speed of at least 74 mph. A tropical cyclone, in turn, is a storm system that develops in the tropics and is characterized by a low pressure center and thunderstorms that produce strong winds, rain, and storm surges. Tropical cyclone is a generic name that refers to the storms' geographic origin and cyclonic rotation around a central eye. Depending on their location and strength, the storms are called different things. What gets dubbed a hurricane in the Atlantic, for example, would be called a typhoon if it happened in the northwestern Pacific.

What's the difference between a hurricane and a tropical storm?

Simply put: Wind speed. When tropical cyclones are just starting out as general areas of low pressure with the potential to strengthen, they’re called tropical depressions. They’re given sequential numbers as they form during a storm season so the National Hurricane Center (NHC) can keep tabs on them.

Once a cyclone’s winds kick up to 39 miles per hour and sustain that speed for 10 minutes, it becomes a tropical storm and the NHC gives it a name. If the cyclone keeps growing and sustains 74 mph winds, it graduates to hurricane.

Once we call it a hurricane, how do we categorize it?

In order to assign a numeric category value to a hurricane, meteorologists look to the Saffir-Simpson Hurricane Wind Scale, which was developed as a classification system for Western Hemisphere tropical cyclones in the late 1960s and early '70s by structural engineer Herbert Saffir and his friend, meteorologist Robert Simpson, who was the director of the NHC at the time.

When Saffir was working on a United Nations project to study low-cost housing in hurricane-prone areas, it struck him that there was no simple, standardized way of describing hurricanes and their damaging effects, like the way the Richter scale is used to describe earthquakes. He created a five-level scale based on wind speed and sent it off to Simpson, who expanded on it to include the effects on storm surge and flooding. Simpson began using it internally at the NHC, and then in reports shared with emergency agencies. It proved useful, so others began adopting it and it quickly spread.

How does the scale work?

According to the NHC, the scale breaks down like this:

Category 1 storms have sustained winds of 74 to 95 mph. These “very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding, and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days."

Category 2 storms have sustained winds of 96 to 110 mph. These “extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks."

Category 3 storms have sustained winds of 111 to 129 mph. This is the first category that qualifies as a “major storm” and “devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes."

Category 4 storms have sustained winds of 130 to 156 mph. These storms are “catastrophicand damage includes: “Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months."

Category 5 storms have sustained winds of 157 mph or higher. The catastrophic damage entailed here includes: “A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months."

While the Saffir-Simpson scale is useful, it isn’t the be-all and end-all for measuring storms, as the National Oceanic and Atmospheric Administration (NOAA) pointed out on Twitter in 2013:

Is there anything worse than a category 5?

Not on paper, but there have been hurricanes that have gone beyond the upper bounds of the scale. Hypothetically, hurricanes could up the ante beyond Category 5 more regularly. The storms use warm water to fuel themselves and as ocean temperatures rise, climatologists predict that potential hurricane intensity will increase.

Both Saffir and Simpson have said that there’s no need to add more categories because once things go beyond 157 mph, the damage all looks the same: really, really bad. Still, that hasn't stopped several scientists from suggesting that maybe the time has come to consider a Category 6 addition.

Timothy Hall, a senior scientist at NASA's Goddard Institute for Space Studies, recently told the Los Angeles Times that if the current global warming trends continue, he can foresee a time—likely by the end of the century—where wind speeds could blow past 230 mph, which could create conditions similar to a F-4 tornado (which has the power to lift cars off the ground and send them hurtling through the air with relative ease).

“If we had twice as many Category 5s—at some point, several decades down the line—if that seems to be the new norm, then yes, we’d want to have more partitioning at the upper part of the scale,” Hall said. “At that point, a Category 6 would be a reasonable thing to do."

An earlier version of this article appeared in 2013.

What’s the Difference Between a Pirate and a Buccaneer?

geniebird/iStock via Getty Images
geniebird/iStock via Getty Images

Talk Like a Pirate Day is returning to port on September 19th and you can bet your boots that a few celebrants will be using the terms pirate and buccaneer interchangeably. Most people do. Nevertheless, these two words aren’t actually synonymous.  

Four hundred years ago, if you were a seafaring thief, the label that you received said a great deal—mainly about whoever it was doing the labeling. Anyone who called you a "pirate" probably hated your guts. But those who cited you as a “buccaneer” might have had a very different attitude. Within certain contexts, the latter group may have even embraced you as a national hero.

Time for a swashbuckling semantics lesson. In article 101 of the United Nations Convention on the Law of the Sea (UNCLOS), piracy is defined as "any illegal acts of violence or detention ... committed for private ends by the crew or the passengers of a private ship." UNCLOS also states that, to be considered piracy, a crime must occur within international waters. If the event in question takes place within a particular country’s territorial waters, the aggressors will be deemed armed robbers rather than pirates.

Historical definitions tended to be a lot broader. During the 17th and 18th centuries, England regarded piracy as any criminal act committed on the high seas or below the low tide mark around shores, rivers, and estuaries. Hundreds of years earlier, in the year 100 CE, Plutarch—a noteworthy Greek scholar— talked about pirates as anybody who attacked a ship or maritime city without legal authority.

Just what did he mean by “legal authority?” Plutarch was probably alluding to warships. Nowadays, these are generally owned by national governments, but this wasn’t always the case. From medieval times through the early 20th century, it was common practice for a nation at war to recruit private vessels to assault its enemy’s ships, steal their goods, and plunder their ports. Mariners who engaged in such state-approved mischief were called “privateers.”

Usually, a privateer vessel was allowed to operate under a license that was granted by the country it served. Dubbed the Letter of Marque, this document laid out a code of conduct and payment policy for the crew. (Privateers almost always got to keep a percentage of whatever they took.)

Essentially, privateers were independent contractors, acting as hostile, government-commissioned, seafaring mercenaries. Therefore, they technically weren’t pirates because real pirates didn’t behave in accordance with any national laws or regulations. But the dividing line here was pretty blurry. Many privateers eventually became pirates and vice versa. Also, a captured privateer would sometimes be tried as a pirate by the country he or she was victimizing.

This brings us back to buccaneers: Throughout the 16th through 18th centuries, Spain more or less controlled the Caribbean. However, in the 1600s, she started to get some not-so-friendly competition. By the middle of that century, settlers from various other European countries—including England, France, and the Netherlands—had colonized parts of the Leeward Islands and Hispaniola. Among these newcomers, transplanted Frenchmen were especially common. The Gallic colonists would frequently smoke their meat over a wooden platform that they called a boucan. Thanks to this cooking technique, the frontiersmen were given the nickname “buccaneers.”

Before long, many turned to piracy. Because of Spain’s huge colonial presence in the Caribbean, buccaneers more or less exclusively targeted Spanish ports and ships. This turned plenty of heads across the Atlantic. In an attempt to cripple Spain’s empire, the English, French, and Dutch began issuing Letters of Marque to buccaneer vessels.

Eventually, the word buccaneer came to possess its current—and very specific—definition, which is: “any of the piratical adventurers who raided Spanish colonies and ships along the American coast in the second half of the 17th century.” (Told you it was specific.)

The most famous buccaneer of them all was undoubtedly Sir Henry Morgan. Little is known about his early life, although most historians believe that he was born in Wales at some point in 1635. Nearly 20 years later, he set sail for Barbados as a member of an expedition that saw England seize Jamaica from the Spanish.

Morgan quickly emerged as a leading buccaneer, and as England’s most ruthlessly effective privateer. In 1668, he seized the heavily guarded city of Porto Bello, Panama, holding it for ransom until the Spanish coughed up an amazing 250,000 pesos. Three years later, Morgan raided and sacked Panama City, which promptly burned to the ground. Such exploits did not endear him to the Spanish, but in England, Morgan was a widely beloved figure. Knighted by King Charles II, he was made Lieutenant Governor of Jamaica in 1674. Following his death on August 25, 1688, Morgan received a grandiose state funeral, complete with a 22-gun salute.

And, yes, that rum was named after him. Clearly, buccaneering had its perks. 

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Why is Friday the 13th Considered Unlucky?

iStock
iStock

Today, people around the globe will feel uneasy about getting out of bed, leaving their homes, or going about their normal daily routines, all because of a superstition. These unfortunate folks suffer from paraskavedekatriaphobia, a common neurosis familiar to us all: the fear of Friday the 13th. But just where did this superstitious association come from, and how did it catch on?

The truth is that no one is absolutely sure where the idea that Friday the 13th is unlucky originated. Donald Dossey, the founder of the Stress Management Center and Phobia Institute in Asheville, North Carolina, suspects the fear can be traced back to a Norse myth about 12 gods who had a dinner at Valhalla—the fabled hall where legendary Norse heroes feasted for eternity after they died—that was interrupted by a 13th guest, the evil and mischievous god Loki.

According to legend, Loki tricked Höðr (the blind god of winter and son of Odin, the supreme god in Norse mythology) into shooting his brother Baldr (the benevolent god of summer who was also a son of Odin) with a magical spear tipped with mistletoe—the only substance that could defeat him. Thus the number 13 was branded as unlucky because of the ominous period of mourning following the loss of such powerful gods by this unwanted 13th guest.

For whatever reason, among many cultures, the number 12 emerged throughout history as a "complete" number: There are 12 months in a year, 12 signs of the zodiac, 12 Gods of Olympus, 12 sons of Odin, 12 labors of Hercules, 12 Jyotirlingas or Hindu shrines where Shiva is worshipped, 12 successors of Muhammad in Shia Islam, and 12 tribes of Israel. In Christianity, Jesus was betrayed by one of his 12 Apostles—Judas—who was the 13th guest to arrive for the Last Supper. Surpassing the number 12 ostensibly unbalances the ideal nature of things; because it is seen as irregular and disrespectful of a sense of perfection, the number 13 bears the stigma of misfortune and bad luck we know today.

WHY FRIDAY?

Friday joins in the mix mostly because all of the early accounts of Jesus’s crucifixion agree that it took place on Friday—the standard day for crucifixions in Rome. As Chaucer noted in The Canterbury Tales, "And on a Friday fell all this mischance." Yet perpetuating Friday as an unlucky day in America came from the late 19th-century American tradition of holding all executions on Fridays; Friday the 13th became the unluckiest of days simply because it combined two distinct superstitions into one. According to the Oxford University Press Dictionary of Superstitions, the first reference to Friday the 13th itself wasn’t until 1913. (So despite actually occurring on Friday, October 13, 1307, the popular notion that the Friday the 13th stigma comes from the date on which the famed order of the Knights Templar were wiped out by King Philip of France is just a coincidence.)

The repercussions of these phobias reverberated through American culture, particularly in the 20th century. Most skyscrapers and hotels lack a 13th floor, which specifically comes from the tendency in the early 1900s for buildings in New York City to omit the unlucky number (though the Empire State Building has a 13th floor). Some street addresses also skip from 12 to 14, while airports may skip the 13th gate. Allegedly, the popular Friday the 13th films were so-named just to cash in on this menacing date recognition, not because the filmmakers actually believed the date to be unlucky.

So, is Friday the 13th actually unlucky? Despite centuries of superstitious behavior, it largely seems like psychological mumbo jumbo. One 1993 study seemed to reveal that, statistically speaking, Friday the 13th is unlucky, but the study's authors told LiveScience that though the data was accurate, "the paper was just a bit of fun and not to be taken seriously." Other studies have shown no correlation between things like increased accidents or injuries and Friday the 13th.

And Friday the 13th isn't a big deal in other cultures, which have their own unlucky days: Greeks and Spanish-speaking countries consider Tuesday the 13th to be the unluckiest day, while Italians steer clear of Friday the 17th. So today, try to rest a little easy—Friday the 13th may not be so unlucky after all.

Additional Source: 13: The Story of the World’s Most Popular Superstition.

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