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How to Build a Category 5 Hurricane

It takes special conditions to breed and feed these rare monster storms.

Learn More: Hurricanes 101

Hurricane Irma has become one of the rare storms to reach Category 5 status, transforming it into a seagoing monster with the power to shred cities.

Category 5 storms are rare, and surprisingly fragile, with particular conditions required to build and maintain them. Most weaken before reaching land, but when they do hit, they’re historic events.

Fueling the Storm

Warm oceans can intensify hurricanes, which

scientists believe thrive when sea surface tem

peratures are above 82 degrees Fahrenheit. As

Hurricane Irma approaches the United States,

warmer waters will provide more energy to fuel

the storm.

Saffir-Simpson Hurricane Wind Scale

Category 5

(157 mph winds or higher)

Category 4

(130-156 mph winds)

Sea surface temperature on Sept. 7, 2017

(Fahrenheit)

76.6

87.4

82.0

United

States

As of Sept. 8, 2017, there is about

a 66 percent chance Hurricane

Irma will move through this area

by Sept. 13, 2017.

FLA.

Atlantic

Ocean

Bahamas

Sept. 7, 2017

Cuba

Haiti

Dom.

Rep.

Jamaica

Puerto

Rico

(U.S.)

Caribbean Sea

Virgin

Islands

(U.S.)

Fueling the Storm

Warm oceans can intensify hurricanes, which scientists believe thrive when sea surface

temperatures are above 82 degrees Fahrenheit. As Hurricane Irma approaches the

United States, warmer waters will provide more energy to fuel the storm.

United

States

Tennesse

North

Carolina

Ala.

S.C.

Miss.

Georgia

Saffir-Simpson Hurricane

Wind Scale

Category 5

(157 mph winds or higher)

Atlantic

Ocean

Category 4

(130-156 mph winds)

As of Sept. 8, 2017, there

is about a 66 percent

chance Hurricane Irma

will move through this

area by Sept. 13, 2017.

Florida

Sea surface temperature

on Sept. 7, 2017

(Fahrenheit)

Gulf of Mexico

Bahamas

76.6

82.0

87.4

Sept. 7, 2017

Cuba

Mexico

Haiti

Dom.

Rep.

Jamaica

Puerto

Rico

(U.S.)

Virgin

Islands

(U.S.)

Caribbean Sea

Lauren C. Tierney, NG STAFF

Sources: National Hurricane Center; NOAA


To reach the top of the five-point Saffir-Simpson Scale, a hurricane’s peak winds must exceed 155 miles per hour. Irma’s have reached 175 miles per hour, enough to do catastrophic damage.

View Images

All but the engine of this train was blown from the tracks of the Florida East Coast Railway by a Category 5 hurricane that struck the Florida Keys in 1935. The train was en route to pick up World War I veterans who had been sent to the Keys to work on a New Deal construction project.


Even a small bump up or down the strength categories can make a big difference in destruction seen at landfall. And the difference between the top and bottom of the scale is much larger than the category numbers might imply. A Category 5 hurricane is likely to do 500 times more damage than a Category 1 hurricane, for instance, which has winds of 95 mph.

“Every mile per hour that the wind speed increases is significant,” said meteorologist Phil Klotzbach of Colorado State University.

But for all its savage power, a Category 5 hurricane is highly dependent on the environment around it to maintain its power.

Hurricanes draw their energy from seawater that has been heated to at least 80 degrees Fahrenheit. To form a Category 5 monster, a storm must not only be fed by warm waters but also can’t encounter too much upper-level wind, known as wind shear, that can break up the development of a hurricane’s counter-clockwise rotation.

Unfortunately for the people in the path of Irma, conditions at present are very favorable for the storm’s continued development. The website Weather Underground reports that the ocean water ahead of the hurricane is a very warm 84 to 86 degrees Fahrenheit. And wind shear is expected to be low for the next several days.

View Images
Homes were reduced to piles of rubble following Hurricane Andrew.

Still, Irma’s intensity could fluctuate thanks to the complex mechanics of powerful hurricanes. Intense storms often undergo a phenomenon known as an eyewall replacement cycle. The eyewall, which contains a hurricane’s most powerful winds, surrounds the calm center of the storm. As a powerful storm travels across open water, a second eyewall can encircle the existing eyewall, causing the first eyewall to disintegrate and weakening the hurricane’s highest winds.

On the other hand, a hurricane can re-intensify after this eyewall cycle is completed if waters are still warm and wind shear is low.

A powerful storm also can lose strength if it passes over a large island. If Hurricane Irma crosses Hispaniola or Cuba, it could be greatly weakened.

View Images
John Burk, foreground and Carl Wilson (top, back) survey the damage to their Long Beach, Miss. house Tuesday, Aug. 19, 1969. Burk was blown into a tree by Hurricane Camille Sunday night and rode out the storm in his perch. Wilson ended up under the house when it collapsed. Neither was injured but two other people in the house died.

Only three hurricanes have made landfall as a Category 5 in recorded U.S. history. A total of 32 reached Category 5 status at least temporarily in the Atlantic Basin since 1924.

  • The Labor Day Hurricane of 1935 came ashore at Long Key, Florida, on September 2, 1935, with winds exceeding 200 miles per hour. About 250 World War I veterans working on a WPA road construction project were killed when administrators failed to get them out ahead of the storm.
  • Hurricane Camille made landfall on August 18, 1969, near Bay Saint Louis, Mississippi, with winds of at least 175 miles per hour. The storm left only a concrete slab where a three-story apartment building had once stood in nearby Pass Christian.
  • Hurricane Andrew slammed into a U.S. Air Force base and a new baseball stadium with winds of 175 miles per hour when it came ashore just south of Miami on August 24, 1992.

When the 1935 Category 5 hurricane hit the Florida Keys, low-lying coral islands off the tip of Florida, very few people lived there. Today, Hurricane Irma poses a grave threat to the Keys. There is only one road in and out for the island’s 75,000 residents, plus tens of thousands of tourists. A complete evacuation takes three days, meaning that emergency management directors must order an evacuation three days before a hurricane is expected to make landfall there.

Listen to IPPY Award-winning author Willie Drye talk about his latest book, For Sale—American Paradise: How Our Nation Was Sold an Impossible Dream in Florida, on NPR affiliates WUNC, Chapel Hill and WLRN, Miami. Visit his blog, Drye Goods, now in its 10th year. Follow him on Facebook.