MIAMI — A storm surge is called dangerous and life-threatening, but what exactly is it?
It's not a wall of water or a tsunami. Simply put, it's when hurricane winds push water toward shore. It can happen quickly and far from a storm's center, inundating areas that don't typically flood.
Storm surges don't just come from the ocean. They can come from sounds, bays, lakes and sometimes well inland.
Large hurricanes tend to create greater storm surges over a broader area, and coastal features such as bays can act like funnels and back water up into rivers and canals, said Jamie Rhome, head of the U.S. National Hurricane Center's storm surge unit.
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About 1,000 miles (1,600 kilometers) of coastline from Tampa Bay to the mid-South Carolina coast could see storm surge. Much of that landscape lies less than 10 feet (3 meters) above sea level, and the surge from Irma could be a few inches higher in some areas.
Much of Florida's southwest coast is uninhabited swampland, including a large section of Everglades National Park.
Storm surge has accounted for half the U.S. deaths from hurricanes, tropical storms and cyclones over the last half-century, according to a hurricane center study.
The surge helped destroy nearly half the structures along a 40-mile stretch of the Florida Keys during the 1935 Labor Day Hurricane, which killed over 400 people, including World War I veterans working on a railway project.
Storm surge flooding up to 28 feet above normal tide levels were associated with Hurricane Katrina in 2005, directly or indirectly causing at least 1,500 deaths, according to the hurricane center.
Even tropical storms can cause major coastal flooding. Hurricane Sandy lost its tropical characteristics before making landfall in 2012, but its enormous size drove catastrophic storm surge onto the New Jersey and New York coastlines.