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Seawater Poses Hurricanes’ Biggest Threat

  • Ocean water rushes down Cape Hatteras Pier Drive in Frisco, N.C., on Hatteras Island as the effects of Hurricane Florence reach the area on Thursday, Sept. 13, 2018. (Steve Earley /The Virginian-Pilot via AP)

  • Isle of Palms Fire Chief Ann Graham, at left, and Isle of Palms police officer Thomas Molino III raise a tropical storm warning flag over the Isle of Palms Connector shortly after Charleston County, S.C., went under a tropical storm warning due to Hurricane Florence Thursday, Sept. 13, 2018, in Isle of Palms, S.C. (AP Photo/Mic Smith)

  • Ocean waters rushes down Hwy 12 in Frisco, N.C., on Hatteras Island as the effects of Hurricane Florence breach the dune line on Thursday, Sept. 13, 2018. (Steve Earley /The Virginian-Pilot via AP)

  • Waves slam the Oceana Pier & Pier House Restaurant in Atlantic Beach, N.C., Thursday, Sept. 13, 2018 as Hurricane Florence approaches the area. (Travis Long/The News & Observer via AP)

  • Waves slam the Oceana Pier & Pier House Restaurant in Atlantic Beach, N.C., Thursday, Sept. 13, 2018 as Hurricane Florence approaches the area. (Travis Long /The News & Observer via AP)

  • Ocean water breeches to the dunes in Avon, N.C., as the first effects of Hurricane Florence reach Hatteras Island on Thursday, Sept. 13, 2018. (Steve Earley/The Virginian-Pilot via AP)

  • Residents at Trent Court Apartments wait out the weather as rising water gets closer to their doors in New Bern, N.C. Thursday, Sept. 13, 2018. Hurricane Florence already has inundated coastal streets with ocean water and left tens of thousands without power, and more is to come. (Gray Whitley/Sun Journal via AP)

  • Jamie Thompson and Ryan Thompson walk through flooded areas along the Neuse River near East Front Street in New Bern, N.C. Thursday, Sept. 13, 2018. Hurricane Florence already has inundated coastal streets with ocean water and left tens of thousands without power, and more is to come. (Gray Whitley/Sun Journal via AP)



AP Science Writer
Monday, September 24, 2018

Behold the awesome power of water. The ocean swallowed beaches, roads and anything else in the way of Hurricane Florence’s monstrous storm surge.

Storm surges aren’t walls of water, like a tsunami. Caused by a hurricane’s winds pushing relentlessly on the shore, they are more like domes of high water that form as the ocean spreads inland. The high water has destructive waves on top that rise above normal tides.

“You are taking the ocean and raising it,” said storm surge expert Hal Needham, director of Marine Weather and Climate in Miami. “It’s not a wave the surfer rides. It’s actually raising the ocean. That’s why it’s so scary.”

Florence’s storm surge was more than 10 feet in parts of North Carolina, according to the National Hurricane Center.

Even if a house is elevated 10 feet, with that kind of storm surge, “there’s a good chance there’s going to be water inside of it,” Needham said.

It’s not just beach areas that are at risk. Storm surge invades rivers and estuaries, too, said National Hurricane Center Director Ken Graham.

“These bays, these rivers and these inlets, there’s so much storm surge the water is being literally forced to flow the opposite direction,” Graham said. “You can get storm surge even several miles inland.”

While hurricane-force winds can rip the roofs off houses, it is the water — storm surge, inland flooding, surf and drowning at sea — that kills nearly 9 out of 10 people in major hurricanes.

And of all those, storm surge is the deadliest. From 1963 to 2012, 49 percent of U.S. hurricane deaths were from storm surge, 27 percent from rain, 8 percent from wind, 6 percent from surf, 6 percent were offshore and 3 percent from tornadoes, according to a National Hurricane Center study.

The deadliest hurricanes to hit the U.S. mainland killed most of their victims with storm surge, including 2005’s Katrina, said Jeff Masters, meteorology director at Weather Underground.

But last year, even with hurricanes Harvey, Irma and Maria, no one in the United States died of storm surge, the National Oceanic and Atmospheric Administration announced. It was the first year that the hurricane center had started new storm surge warnings. Mostly people are getting better at evacuating, with three-quarters of the Florida Keys fleeing before Irma, Masters said.

Storm surge is also the source of vast amounts of damage. Masters estimated that storm surge caused at least $3 billion in damage, compared with maybe $1 billion for wind damage. Damaged or destroyed buildings are often rebuilt in the same surge-prone areas, with government aid, he said.

Needham, who drove all night from Miami to North Myrtle Beach, S.C., to watch and record the Florence storm surge from the relative safety of a parking garage, said the surge had “already gobbled up the beach” there.

“It’s just going to be an interesting ride,” Needham said. “I could not sit home and watch it on TV. I had to be there.”

The worst storm surge comes in with a hurricane’s eye, and it arrives “with a lot of debris to batter you, and it’s not particularly survivable,” Masters said.

Storm surge is higher in the right-front quadrant of a storm because the system’s counterclockwise motion pushes more water inland, Masters said. Sometimes in the opposite quadrant there’s a reverse storm surge that makes the ocean retreat. That’s particularly dangerous because the ocean comes back quickly with 6 feet or more of water.

Storm surge is higher when the water just off the beach is shallower, Needham said. Think of it like a giant aquarium filled to the brim. If a large rock in thrown in, it spills over. But if the aquarium is not full, it’s only a ripple.

Tides are another factor. The surge is highest when the tides are high. The coast of the Carolinas is about middle of the road with about 4 to 5 feet of difference between high and low tides.

The shape of the coastline is another factor. If it is bowl-shaped, like in Georgia and South Carolina, the surge is deeper, but when it is the opposite shape, like the Outer Banks, it’s less so, Needham said.

Seas have risen from global warming, making all of this even worse. In Wilmington, N.C., the sea level is close to 8 inches higher than in 1935, according to NOAA. Those few inches can mean the difference between staying dry and enduring costly damage.

Associated Presswriter Jennifer Kay in Miami contributed to this report.