Hurricanes are categorized by their wind speeds on the Saffir-Simpson Hurricane Scale. The scale was first developed by Herb Saffir, a structural engineer, and Bob Simpson, a meteorologist.
Category 1: winds between 74 m.p.h. and 95 m.p.h.
Category 2: winds between 96 m.p.h. and 110 m.p.h.
Category 3: winds between 111 m.p.h. and 129 m.p.h.
Category 4: winds between 130 m.p.h. and 156 m.p.h.
Category 5: winds of 157 m.p.h. or greater.
To be considered a “major” hurricane, according to the National Hurricane Center, a storm must reach Category 3 or above.
A hurricane’s strength matters because it helps meteorologists give residents in its path an idea of what type of damage is possible.
A Category 2 hurricane, for example, has the potential to cause major roof damage to homes, snap or uproot shallowly rooted trees, and knock out power in an area for days to weeks.
When a hurricane reaches Category 5 strength, the center can predict that “catastrophic damage will occur,” according to the Saffir-Simpson scale. Winds from a Category 5 hurricane can destroy homes, fell trees and power lines and possibly leave an area without power for weeks or months.
Because the hurricane category scale is based only on wind speeds, a number of factors are not considered.
“Wind is only one of four hazards, four primary hazards, associated with a tropical cyclone,” said Dr. Michael Brennan, the acting deputy director of the National Hurricane Center, using the broader term for a hurricane. “You can also have rainfall and flooding, storm surge, tornadoes, rip currents.”
Other hurricane-related dangers can occur after the storms have moved through an area.
When an affected area loses power, for example, many people often turn to portable generators to produce electricity. But when they are used improperly, they can lead to carbon monoxide poisoning.
And a weak Category 1 hurricane, or even a tropical storm, can still cause serious damage. A tropical storm can have wind speeds between 39 m.p.h. and 73 m.p.h. If the storm strengthens and produces winds up to 74 m.p.h., it becomes a Category 1 hurricane.
“There’s very little difference — and almost an imperceptible difference — between a strong tropical storm that has, say, maximum sustained winds of around 70 m.p.h., and a Category 1 hurricane,” Dr. Brennan said. “There’s enough uncertainty there that those distinctions — 1 m.p.h. or even 5 m.p.h. — doesn’t make a big difference.”