Why storm surge is a hurricane's greatest threat

Florida Gov. Rick Scott warned residents that Hurricane Irma could bring a potentially deadly storm surge when the storm passes along the state’s west coast.

“The threat of significant storm surge flooding along the entire west coast of Florida has increased,” Scott said in a Saturday morning news conference. He said the storm surge could be as high as to 6 to 12 feet. “This will cover your house.”

With Hurricane Harvey and now Hurricane Irma threatening states along the Gulf Coast, we’ve been hearing a lot about storm surges and how big of a threat they pose to coastal communities.

But privately, you may be wondering (and you wouldn’t be alone): “What is a storm surge?”
A storm surge is a gradual rise in the water level caused by a major storm’s wind as it gets closer to shore.

“As the storm approaches the coast,” said CNN meteorologist Gene Norman, “it increases the water level by sending those waves inland.”

Winds from the storm push the water toward the shore, Norman said. But that water doesn’t just come in and go back out.

Over time, as each wave comes in, that water will slowly begin to accumulate, raising the average water level onshore — similar to a tide — until it swallows up a beach or rises over a pier, causing flooding. All of this can be made worse by the waves that ride in on top of the shore, however big or small they may be.

And again, the water doesn’t just leave. Depending on how much water was pushed ashore, and the area’s watershed, that water may hang around. For instance, Norman said, “if it comes to the Everglades, well, that place is mostly water. So it’s going to take a while.”

The National Hurricane Center says storm surge is “often the greatest threat to life and property from a hurricane,” and Norman agrees.

“Storm surge is the most dangerous part of any hurricane threat,” Norman said, adding that the danger grows as the water begins to destroy structures on land. Storm surge can tear apart buildings and the resulting debris is added to the deadly churning water.

Saturday, the hurricane center said parts of Florida’s southwest coast could see “catastrophic” storm surge, 10 to 15 feet high. It’s one of the reasons officials have told residents that moving even just a few miles inland could be beneficial for them.

“You will not survive all this storm surge,” Gov. Scott said Saturday. “This is a life-threatening situation.”

CNN’s Gene Norman and Judson Jones contributed to this report.