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.

This Smart Accessory Converts Your Instant Pot Into an Air Fryer

Amazon
Amazon

If you can make a recipe in a slow cooker, Dutch oven, or rice cooker, you can likely adapt it for an Instant Pot. Now, this all-in-one cooker can be converted into an air fryer with one handy accessory.

This Instant Pot air fryer lid—currently available on Amazon for $80—adds six new cooking functions to your 6-quart Instant Pot. You can select the air fry setting to get food hot and crispy fast, using as little as 2 tablespoons of oil. Other options include roast, bake, broil, dehydrate, and reheat.

Many dishes you would prepare in the oven or on the stovetop can be made in your Instant Pot when you switch out the lids. Chicken wings, French fries, and onion rings are just a few of the possibilities mentioned in the product description. And if you're used to frying being a hot, arduous process, this lid works without consuming a ton of energy or heating up your kitchen.

The lid comes with a multi-level air fry basket, a broiling and dehydrating tray, and a protective pad and storage cover. Check it out on Amazon.

For more clever ways to use your Instant Pot, take a look at these recipes.

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What Do Pets See When They Watch Television?

This dog would like to turn off Netflix's autoplay feature.
This dog would like to turn off Netflix's autoplay feature.
Amatore/iStock via Getty Images

In 2012, a television commercial aired in the UK for Bakers dog food that was conceived and produced specifically to attract the attention of dogs. The spot used high-frequency sounds that are inaudible to human ears. In theory, the dog would be so captivated by the advertisement that owners would take note and perhaps purchase Bakers for their next meal.

This didn’t quite work. Many dogs failed to react at all, proving that when it comes to television ads, humans may be more impressionable than canines.

While pets may not be so easily manipulated, they still find the television screen interesting, sometimes reacting to other dogs, animals, sounds, or images. But what is a dog really seeing when they tune in?

When it comes to color, television is no different from reality for a dog. They have dichromatic vision, which means they see the world through the range of two primary colors, yellow and blue. (Humans have trichromatic vision, able to see the full color spectrum.) Cone cells in canine eyes are also believed to blur their sight to a degree. More importantly, dogs process the frame rate, or “flicker fusion frequency,” of screens differently than people. Humans can detect movement at between 16 and 20 frames per second. Dogs need 70 frames per second or more. If they’re looking at an older television, it might resemble a flip book or even a strobe light effect to them. (Modern sets have a faster frame rate, which is why dogs might be more interested in your high-definition television.)

That helps explain the visuals. What about the content? Typically, dogs will react to the same things that would draw their attention in a room—barking, squeaking toys, or commands. In a study published in Animal Cognition in 2013, nine dogs were observed to see if they could pick out the face of another dog—regardless of breed—on a computer screen instead of another animal or a person. The dogs were rewarded with treats with a successful choice. Though the sample size was small, it indicated dogs can recognize other dogs on a screen. (Which you likely already knew if you’ve ever observed your dog suddenly on alert when a canine appears on camera.)

If your dog used to get excited by another dog on television but has since lost interest, it’s possible they simply became desensitized to their appearance, realizing the image in front of them isn’t going to move out of the boundaries of the monitor.

Content unrelated to dogs might not be of much interest. In a 2017 study published in the International Journal of Human-Computer Studies, dogs presented with three different viewing screens didn’t exhibit any particular preference for one over the other. If they were shown three screens at one time, they seemed uninterested in watching anything at all.

The study also noted that dogs had a limited television attention span. Rather than mimic the binge-watching habits of humans, dogs prefer to glance at a screen for a few seconds at a time. But that behavior could also be breed-specific. Dogs bred for hunting might be interested in moving objects, while dogs that rely more on smell might be indifferent.

And what about cats? In a study published in Applied Animal Behaviour Science in 2008, 125 shelter cats were given a television to view for up to three hours a day. The cats were split into five groups and given a variety of programming to watch, from humans to footage of prey to a blank screen. On average, cats spent just 6.1 percent of the observation time watching the screen. When they did, it was mostly to focus on the prey.

Because cats may react to images of birds and rodents on television, owners should avoid letting them watch unattended. You can also secure the set to a wall to make sure they don’t knock it down.

For the most part, dogs and cats are far more interested in what’s going on in the real world compared to what's on TV. We could probably take a lesson from their limited screen time.