Tropical Storm Debby has strengthened into a Category 1 hurricane as it approaches Florida.

Forecasters at the National Hurricane Center in Miami said on Sunday evening the storm had maximum sustained winds of 75mph.

Debby is the fourth named storm of the 2024 Atlantic hurricane season after Tropical Storm Alberto, Hurricane Beryl and Tropical Storm Chris, all of which formed in June.

Forecasters warned that heavy amounts of rain could bring catastrophic flooding in Florida, South Carolina and Georgia.

Tropical Storm Florida
A vehicle drives through a flooded street as Tropical Storm Debby approaches Florida. (Dylan Townsend/Tampa Bay Times via AP)

A tornado watch was also in place for parts of Florida and Georgia until 6am on Monday.

“Right now, we are trying secure everything from floating away,” said Sheryl Horne, whose family owns the Shell Island Fish Camp along the Wakulla River in St Marks, Florida, where some customers moved their boats inland.

Debby was expected to move eastward over northern Florida and then stall over the coastal regions of Georgia and South Carolina, thrashing the region with potential record-setting rains totalling up to 76 centimetres beginning Tuesday local time

Officials also warned of a life-threatening storm surge along Florida’s Gulf Coast, with six to 10 feet of inundation expected Monday between the Ochlockonee and Suwannee rivers.

“There’s some really amazing rainfall totals being forecast and amazing in a bad way,” Michael Brennan, director of the hurricane centre, said at a briefing.

“That would be record-breaking rainfall associated with a tropical cyclone for both the states of Georgia and South Carolina if we got up to the 30-inch level.”

Flooding impacts could last until Friday and are expected to be especially severe in low-lying areas near the coast. North Carolina officials were monitoring the storm’s progress.

Officials in Savannah said the area could see a month’s worth of rain in four days if the system stalls over the region.

At a briefing on Sunday afternoon, Florida Governor Ron DeSantis warned that the storm could lead to “really, really significant flooding that will happen in North Central Florida.”

He said it would follow a similar track to Hurricane Idalia but would “be much wetter. We are going to see much more inundation”.

Tropical storms and hurricanes can trigger river flooding and overwhelm drainage systems and canals.

Mr DeSantis declared a state of emergency for 61 of Florida’s 67 counties, with the National Guard activating 3,000 guard members. Utility crews from in and out of state were ready to restore power after the storm, he said in a post on X.

Georgia Governor Brian Kemp and South Carolina Governor Henry McMaster also made their own emergency declarations.