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AP Explains: How hurricanes unleash deadly floods

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

WASHINGTON – See the awesome power of water. Already the ocean is swallowing beaches, roads and anything else in the way of the Hurricane Florence monstrous storm surge. Storm surges are not the walls of water, like a tsunami, as is often thought. Caused by a hurricane the wind to push relentlessly on the shore, they are more like the domes of high water that form as the ocean spreads in the interior. The high water has destructive waves on top, and it is in addition to the normal tides.

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

Florence storm surge will likely be 7 to 11 feet (more than 2 to 3 meters) above the ground in parts of North Carolina, according to the National Hurricane Center. Other areas can expect the increase to be taller than the average person — almost 6 feet (2 meters) or higher.

Even if a house is elevated 10 feet (3 meters), with that kind of storm surge, “there is a good chance that there is water in,” Needham said.

With Florence slowly and turn, the storm surge is going to be a larger, longer-term factor than normal because the water just keeps piling up,” Needham said.

It is not just about beach areas that are at risk. Storm surge invades rivers and estuaries, also. And the National Hurricane Center Director Ken Graham said that is a special make with Florence.

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

While the hurricane-force winds can rip the roofs off houses, the water — storm surge, flooding, browsing, and drowning in the sea — that kills nearly 9 out of 10 people in the hurricanes, such as Florence.

And of all those, storm surge is one of the deadliest. From 1963 to 2012, 49 percent of the AMERICAN hurricane which were the result of the storm surge of 27 percent of rain, 8 percent from wind, 6 percent of surf, 6% offshore and 3 percent of all 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, says Jeff Masters, meteorology director of 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 was started new storm surge warnings. Usually, people are getting better at evacuate, with three-quarters of the Florida Keys on the flight for Irma, Masters said.

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

Needham, who was riding in the night from Miami to North Myrtle Beach, South Carolina, view and record of the storm surge from the relative safety of a parking garage, said the storm surge had “already swallowed up the beach”.

“It’s just an interesting ride,” Needham said. “I can’t sit at home and watch on the TV. I had to be there.”

The worst storm surge with a hurricane is the eye, and that comes”, with a lot of debris to batter you, and it is not particularly survival,” Masters said.

Storm surge is higher in the right-front quadrant of a storm, because the system of the movement against the clock pushes more water in the interior, Masters said. Sometimes in the opposite quadrant, there is a reverse storm surge that makes the ocean retreat. That is especially dangerous because the ocean comes back quickly with a 6 foot (2 meters) or more of the water.

Storm surge is higher when the water is close to the beach and is shallower, Needham said. Think of it as a giant aquarium filled to the brim. If a large rock is thrown, it runneth over. But if the aquarium is not full, it is just a ripple.

Tides are another factor. The increase is highest when the tides are high. The coast of south Carolina is about the middle of the road with about 4 to 5 meters of difference (1.2 to 1.5 metres between high and low tide.

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

Seas are rising from global warming, which makes this all even worse. In Wilmington, North Carolina, the sea level is close to 8 inches (20 cm) higher than in 1935, according to NOAA. Those few inches can mean the difference between staying dry and endure costly damage.

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Associated Press Writer Jennifer Kay in Miami contributed to this report.

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Follow Seth Borenstein on Twitter: @borenbears . His work can be found here .

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The Associated Press Health & Science Department receives support from the Howard Hughes Medical Institute, Department of science Education. The AP is solely responsible for all content.

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For the latest news on Hurricane Florence, visit https://www.apnews.com/tag/Hurricanes .

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