Tropical storm Debby floods parts of southeastern United States

Tropical storm Debby has moved into some of America's most historic Southern cities, bringing prolonged downpours and flooding after slamming into Florida and prompting the rescue of hundreds.

Record-setting rain from the storm that killed at least five people in Florida and Georgia was causing flash flooding, with up to 64 centimetres possible in some areas, the National Hurricane Center said in its latest advisory Tuesday morning.

"Hunker down," Van Johnson, mayor of Savannah, Ga., told residents in a social media livestream Monday night. He warned people that Tuesday will likely be a "rough day."

The storm's centre was just southwest of Savannah early Tuesday, with maximum sustained winds near 75 km/h.

"Tropical cyclones always produce heavy rain, but normally as they're moving, you know, it doesn't accumulate that much in one place," said Richard Pasch of the National Hurricane Center. "But when they move very slowly, that's the worst situation."

Tropical cyclones derive their energy from warm water, so Debby has weakened over land. But part of the circulation was interacting with water over the Atlantic, Pasch said. The storm's centre is expected to move out over the water off the Georgia and South Carolina coast, then move back inland, so it could restrengthen Wednesday before it moves inland Thursday over South Carolina, he said.

More than 15 centimetres of rain had fallen through Monday at Savannah's airport, and showed no signs of stopping Tuesday, the National Weather Service reported. That's already a month's worth of rain in a single day: In all of August 2023, the city got 14.1 centimetres of rain.

Flash flood warnings were issued in Savannah and Charleston, among other areas of coastal Georgia and South Carolina. Both Savannah and Charleston announced overnight curfews as the rains picked up. Charleston County Interim Emergency Director Ben Webster called Debby a "historic and potentially unprecedented event."

Charleston authorities said police were barricading all eight roads leading into the 350-year-old city built on a marshy peninsula, letting only essential workers and emergency personnel in and urging all non-residents to leave Monday night.

"We need people to make their way out. This is not something you can stay at the bar until 10:45. We need you to take this seriously," Charleston Mayor William Cogswell said.

Charleston also opened parking garages so residents could park their cars above floodwaters and updated an online mapping system to show which roads are closed due to flooding.

A tornado touched down in Edisto Beach, S.C., Monday night, damaging homes and blowing down trees and power lines, the Colleton County Sheriff's Office said on social media. No injuries were immediately reported there officials said.

The weather service continued issuing tornado warnings well into Monday night for parts of the state including Hilton Head Island.

Debby made landfall along the Gulf Coast of Florida early Monday as a Category 1 hurricane. Weakening winds made it a tropical storm again, but its slow forward movement and the the ocean water it picked up caused catastrophic in places.