Isaias drenches southern US as weakened post-tropical cyclone

The southeastern United States faced flooding and tornado risks on Saturday as Isaias, weakened from a hurricane to a post-tropical cyclone, advanced northward from its landfall on Florida's Gulf Coast.

More than 600,000 US customers were without electricity Saturday afternoon along the storm's path through Florida, Alabama and Georgia, according to the PowerOutage.com tracker.

Isaias roared ashore late Friday as a Category 2 hurricane near the resort community of Destin, Florida, packing sustained winds of 105 miles (165 kilometers) per hour, before weakening overnight, the National Hurricane Center (NHC) said.

It was the first hurricane of an Atlantic season tamed by a historic El Nino weather phenomenon, and the first hurricane since 2024 to hit the US mainland.

In Mary Esther, a coastal community near Destin, Matt Howard said he was fortunate the storm weakened ahead of landfall.

Despite losing power and having his neighbor's metal shed crash into his backyard, "overall, we were okay," he told AFP.

"We hunkered down, got in the center of our house, and did all the things you're supposed to do, and luckily came out on the other side," he said.

Officials have reported at least three deaths related to the storm, including two from trees falling on homes -- one near Pensacola in Florida and another in Birmingham, Alabama.

AFP reporters saw several overturned vehicles, downed trees and power lines, and numerous buildings with damaged roofs.

Streets along the coast were largely deserted after authorities ordered mandatory evacuations ahead of the storm.

Florida Governor Ron DeSantis warned at a briefing Saturday afternoon that the threat of flooding remained from rising rivers.

"Just be careful out there. Downed power lines, standing water, any of that can be very, very hazardous. Don't run any generators inside your home or inside your garage," he said.

The governor's warning came after a man was found dead in Florida earlier in the day with a generator running in his garage, CNN reported.

A major flood threat remained as the storm headed northward and inland. The NHC warned that some areas in the southeast could see upwards of 10 inches (25 centimeters) of rain.

"Considerable flash flooding and landslides are also possible across the Southern Appalachians," it warned in a briefing.

The threat was particularly worrying in the mountains of North Carolina, where communities are still recovering from hurricane Helene of 2024.

That storm made landfall in the same Florida region as Isaias, but remained at tropical storm strength as it moved northward, dumping record amounts of rainfall into the mountains and leading to deadly flooding.

Isaias's late arrival this season is largely due to an El Nino of historic strength.

El Nino, the warm phase of the El Nino-Southern Oscillation (ENSO), creates strong vertical wind shear over the Atlantic that tends to tear storms apart. 

"We have been seeing basically nearly record strong shear throughout the Atlantic Basin this year, and that is consistent with what we'd expect to see with a strong El Nino event," Michael Fischer, of the University of Miami's Rosenstiel School of Marine, Atmospheric, and Earth Science, told AFP.

In the Pacific, it has the opposite effect, weakening shear and allowing storms to grow. The Pacific has already produced several hurricanes this year, some of which hit maximum Category 5 strength.