Buzz
The 2022 hurricane season has really picked up steam: Hurricane Ian, after crossing Cuba, is now barreling toward Florida's west coast. By now, we're used to hearing about hurricanes and estimating the damage they may cause based on their category. But how exactly do meteorologists classify these dangerous storms, and what is the scale they use?
A brief overview: Hurricanes are tropical cyclones in the Atlantic Ocean with winds reaching at least 74 mph. Tropical cyclones are storms that form in the tropics, characterized by a low-pressure center and thunderstorms that produce strong winds, rain, and storm surges. The term 'tropical cyclone' refers to the storm's location and its cyclonic rotation around a central eye. Depending on where they occur and their strength, these storms have different names. For example, what we call a hurricane in the Atlantic would be referred to as a typhoon in the northwestern Pacific.
What distinguishes a hurricane from a tropical storm?
In simple terms: Wind speed. Tropical cyclones begin as low-pressure systems with the potential to intensify. Initially called tropical depressions, they are assigned sequential numbers as they form during a storm season to help the National Hurricane Center (NHC) track them.
When a cyclone's winds reach 39 mph and maintain that speed for 10 minutes, it becomes a tropical storm and is given a name by the NHC. If the storm continues to strengthen, with winds reaching 74 mph, it is classified as a hurricane.
Once a cyclone is classified as a hurricane, how do we categorize it?
To assign a category to a hurricane, meteorologists turn to the Saffir-Simpson Hurricane Wind Scale, a system created in the late 1960s and early ’70s by structural engineer Herbert Saffir and meteorologist Robert Simpson, then director of the NHC, to classify tropical cyclones in the Western Hemisphere.
While working on a United Nations project to explore low-cost housing in hurricane-prone regions, Saffir realized there was no standardized method to describe hurricanes and their destructive effects, similar to how the Richter scale is used for earthquakes. He devised a five-level scale based on wind speed and shared it with Simpson, who expanded it to include storm surge and flooding effects. Simpson began using it within the NHC and in reports to emergency agencies. Its usefulness led to broader adoption, and it became widely used.
How is the Saffir-Simpson scale applied?
The NHC explains the scale as follows: Category 1 storms have sustained winds between 74 and 95 mph. These ‘very dangerous winds will cause some damage: Well-built homes may experience roof, shingle, vinyl siding, and gutter damage. Large tree branches will snap, and trees with shallow roots may fall. Power lines and poles will likely be damaged, causing outages that could last from a few days to several days.”
Category 2 storms have sustained winds between 96 and 110 mph. These ‘extremely dangerous winds will result in extensive damage: Well-constructed homes may face severe roof and siding damage. Numerous shallow-rooted trees may be snapped or uprooted, blocking many roads. Power loss is expected, with outages lasting from several days to weeks.”
Category 3 storms have sustained winds between 111 and 129 mph. This is the first category considered a ‘major storm,’ and ‘devastating damage will occur: Well-built homes may experience major damage, including removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking roads. Electricity and water will be unavailable for days to weeks after the storm has passed.”
Category 4 storms have sustained winds between 130 and 156 mph. These storms are deemed ‘catastrophic,’ with damage such as: ‘Well-built homes may suffer severe damage, including loss of most of the roof structure or parts of exterior walls. Most trees will be snapped or uprooted, and power poles will be downed. Fallen trees and power poles will isolate residential areas. Power outages could last weeks to even months. Most areas will be uninhabitable for weeks or months.”
Finally, Category 5 storms feature sustained winds of 157 mph or more. The resulting catastrophic damage includes: 'A large portion of framed homes will be destroyed, with complete roof failure and wall collapse. Fallen trees and power poles will block access to residential areas. Power outages will last from weeks to possibly months. Most of the area will remain uninhabitable for weeks or months.'
Is there a storm worse than a Category 5 hurricane?
Not officially, but there have been hurricanes that have exceeded the scale's maximum limits. As ocean temperatures rise due to climate change, this could become a more frequent occurrence. Climatologists predict that hurricanes' potential intensity will grow as they rely on warm water to fuel their strength.
Both Saffir and Simpson have noted that there’s no need to add more categories, since once wind speeds surpass 157 mph, the damage becomes uniformly severe. Despite this, some scientists have proposed considering the introduction of a Category 6.
Timothy Hall, a senior scientist at The Climate Service, told the Los Angeles Times in 2018 that if global warming trends continue, wind speeds could exceed 230 mph by the end of the century, creating conditions similar to an F-4 tornado—strong enough to lift cars off the ground and send them flying through the air with ease.
'If we experience twice as many Category 5 storms in the future—decades down the line, assuming that becomes the new norm—then yes, it would make sense to further differentiate the upper part of the scale,' Hall remarked. 'At that point, introducing a Category 6 would be a logical step.'
Earlier, this article was published in 2013; it has now been updated for 2022.
