Hurricane Helene reached Florida’s Gulf Coast late Thursday as an “extremely dangerous Category 4 hurricane,” forcing mandatory evacuations for several counties as its deadly storm surge reached up to 20 feet, triggering millions of power outages in the southeast.
Helene is the first known Category 4 storm to hit Florida’s Big Bend region since records began in 1851, according to Colorado State University senior hurricane scientist Phil Klotzbach.
The storm weakened to a tropical storm early Friday morning as it barreled through Georgia, causing life-threatening flooding in Atlanta and the Carolinas. As of the 8 a.m. ET advisory from the NHC, the storm was located about 35 miles south-southwest of Clemson, South Carolina, with maximum sustained winds near 60 mph.
The hurricane center said Helene was moving north and expected to turn northwestward and slow down over the Tennessee Valley later Friday and Saturday. Continued weakening of the storm is expected, as Helene is expected to become a post-tropical low Friday afternoon or evening, the NHC said.
“However, damaging wind gusts will penetrate far inland across the southeastern United States, including over the higher terrain of the southern Appalachians,” the NHC said in the advisory.
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How does a storm surge happen?
While Helene has weakened to a tropical storm, it is still unleashing life-threatening storm surge, winds and flooding rain to portions of the southeastern United States Friday morning.
In the open ocean, hurricane winds push water toward the center of the storm. Instead of piling up, the water spirals downward and flows outward.
As the water is pushed downward, some is pushed out to sea and some is pushed toward the coast.
As the storm approaches land and shallow water, the ocean floor blocks the outflowing water, causing the ocean to surge onto land.
The ocean floor and shape of the coast can influence the height of storm surge – the difference between water levels when a storm approaches. Along the Gulf of Mexico, wide, gently sloping continental shelves make the coastline more vulnerable to water piling up. On the Atlantic coast, narrower shelves with steep slopes produce a lower surge.
