Understanding the Categories of Hurricanes

By: John Perritano  | 
Hurricane Irma
Hurricane Irma reached a maximum sustained wind speed of 185 miles per hour (297 kph), making it the strongest hurricane to ever form in the Atlantic Ocean. NOAA

When the calendar flips to June 1, marking the onset of the hurricane season, phrases like "storm surge," "wind speed" and "eyewall" become all too familiar, especially in the U.S.

But knowing these words isn't enough if you do not have an understanding of the categories of hurricanes. The difference between a Category 1 and a Category 5 hurricane can be the difference between minor damage and utter devastation.


What Is a Hurricane?

Hurricanes, some of the most violent storms on Earth, originate as tropical disturbances near the equator. Here, warm water, moist air and Earth's rotational movement come together to form powerful winds, clouds and thunderstorms.

As these disturbances move across the ocean, warm, moist air rises and is replaced by cooler air. The cooler air condenses and falls toward the ocean surface only to be warmed again. The cycle repeats itself, and tropical disturbances gain strength and spin faster as wind picks up speed and more moist, warm air is pulled upward.


When wind speed reaches 25 to 38 miles (45 to 61 kilometers) per hour, the tropical disturbance morphs into a tropical depression, which turns into a tropical storm when winds reach 39 miles (62 kilometers) per hour.

When Winds Become Storms

Tropical storms are like giant wet vacs on steroids — they suck a generous amount of moisture and heat from the ocean water, adding more fuel to the growing storm. An eye begins to form as the winds turn counterclockwise at staggering speeds. A hurricane is born when winds are clocked at 74 miles (119 kilometers) per hour.

As the storm pushes across the ocean, it gathers speed and strength. Low air pressure forces ocean water into a huge mound near the eye, which could create a devastating storm surge when the wall of water reaches land. The more heat and moisture a hurricane consumes, the more powerful the storm becomes.


The Saffir-Simpson Hurricane Wind Scale

In 1969, during Hurricane Camille's rampage, Robert H. Simpson, then director of the National Hurricane Center, felt the need for a system to communicate the severity of hurricanes.

"I wasn't able to communicate with people, like the Office of Emergency Planning, the American Red Cross, the Salvation Army and all the state agencies that were preparing for the storm," Simpson lamented in the book Hurricane Watch: Forecasting the Deadliest Storms on Earth. "I couldn't get a handle on the storm to answer their question: 'What kind of resources must we put in this particular area to do our job?' I needed something to give them a handle on it, so they would need to know what resources they needed to deal with the storm."


Herbert S. Saffir, an engineer working on wind-resistant building codes, further emphasized this need. Saffir developed a table detailing wind-caused building damage at various speeds. By 1972, Simpson integrated Saffir's findings with storm surge estimates and barometric pressure, giving birth to the Saffir-Simpson hurricane wind scale.

By 1975, this scale was widely adopted, offering a clear, easy-to-understand metric of a hurricane's potential impact.


Breaking Down Hurricane Categories

While the Saffir-Simpson scale is invaluable, it doesn't capture the full essence of a hurricane's might. For instance, a Category 5 hurricane is 500 times more potent than a Category 1. In terms of property damage, a Category 2 can cause seven times the damage of a Category 1, while a Category 5 can wreak 144 times the destruction.

Category 1

These hurricanes entail sustained winds of 74 to 95 miles (119 to 153 kilometers) per hour. These dangerous winds can damage roofs, snap tree branches and uproot some trees. Expect power outages. The storm surge can rise between 4 to 5 feet (1.2 to 1.5 meters).


Category 2

These storms boast sustained winds of 96 to 110 miles (154 to 177 kilometers) per hour. These very dangerous winds can cause extensive damage, including power outages, blocked roads, and major roof and siding damage to well-constructed frame homes. Storm surges can reach up to 8 feet (2.4 meters).

Category 3

With sustained winds of 111 to 129 miles (178 to 208 kilometers) per hour, these major hurricanes can cause severe damage. Post-storm, areas might lack electricity and water for weeks. Storm surges can vary between 9 and 12 feet (2.7 and 3.6 meters).

Category 4

These hurricanes, with winds of 130 to 156 miles (209 to 251 kilometers) per hour, can cause devastating damage. Most trees will be uprooted or snapped, power lines will be downed and areas might be uninhabitable for weeks or even months. Storm surges range between 13 and 18 feet (3.9 and 5.4 meters).

Category 5

These are the most intense hurricanes, with sustained wind speeds exceeding 157 miles (252 kilometers) per hour. Expect catastrophic damage: total roof failures, wall collapses and neighborhoods isolated due to fallen trees and power lines. Storm surges can surpass 18 feet (5.4 meters).