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Hurricane Irma: Eight things to know about Category 5 storms

Published Sep. 6, 2017

If Hurricane Irma makes landfall as a Category 5 storm, it would join a small group of historical storms: It would be only the fourth Category 5 storm to descend on the United States.

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Irma has already raked over the northern Leeward Islands, ripping roofs off buildings and knocking out communication. The powerful storm, packing maximum winds of 185 mph, doesn't show signs of weakening as it chugs west toward Florida.

Here's everything you need to know about Category 5 storms:

• Since 1924, there have been 32 storms that formed in the Atlantic Basin, including the Caribbean and Gulf of Mexico, that strengthened into Category 5 hurricanes at some point during their lives. That now includes Irma. A few other famous Category 5s from recent memory: Hugo in 1989, Ivan in 2004, Katrina in 2005, Felix in 2007 and Matthew last year.

• Every Category 5 storm eventually struck land. But it's exceptionally rare for a hurricane to make landfall in the U.S. as a Category 5. In fact, only three have ever done it: the "Labor Day" storm that slammed into the Florida Keys in 1935; Hurricane Camille, which devastated the Mississippi coast in 1969; and Hurricane Andrew, which rolled over South Florida in 1992.

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• Category 5 storms include sustained winds of at least 157 mph measured 33 feet from the ground. Winds that powerful can destroy homes and topple power poles. In 2004, Tampa Bay Times reporters observed Hurricane Charley strip the paint off of a car. And Charley was only a Category 4.

• Irma's sustained winds have topped more than 180 mph. That's not twice as powerful as 90 mph winds. Why? The damage done by wind power is exponential. Think of it this way: A storm with 180 mph wind speeds could easily cause more than twice as much damage as a Category 4 storm packing 135 mph winds.

• Most Atlantic seasons don't have any Category 5 storms. In 2005, four storms — Emily, Katrina, Rita and Wilma — reached that status, the most of any year. When they do form, September is the most active month with 17 storms.

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• Most of the Category 5 hurricane spent between 10 and 24 hours at that strength. The "Cuba" hurricane in 1932 spent 78 hours as a Category 5, the longest tenure on record. Hurricane Allen in 1980 remained a Category 5 for a total of 72 hours.

• The Category 5 storms that struck Florida brought death and destruction. Hurricane Andrew developed rapidly from a tropical depression into a powerful storm with winds up to 165 mph. After weakening over the Bahamas, it strengthened again before barreling through a cluster of cities south of Miami. The force ripped homes from their foundations, leaving more than 160,000 people homeless and causing $20 billion in property damage.

• Almost 60 years before, on Labor Day 1935, a compact cyclone mowed through the Florida Keys with winds reaching 185 mph. A train was dispatched to evacuate World War I veterans in the area assigned to build a highway from Miami to Key West. But it came too late. More than 400 workers and residents drowned, many of their bodies carried out to sea. Telegraph lines and railroad tracks washed away. The landscape was stripped bare.

Sources: National Hurricane Center, National Weather Service, Massachusetts Institute of Technology, National Oceanic and Atmospheric Administration