Tropical Storm Florence was expected to strengthen back into a hurricane by Saturday night, as forecasters warned that the storm would bring life-threatening rip currents to the US East Coast before possibly making landfall next week.

Florence was spinning across the Atlantic Ocean about 830 miles (1,340 km) southeast of Bermuda on Saturday morning, moving west at around 7 miles per hour (11 kph), according to the Florida-based National Hurricane Center (NHC).

The storm will intensify rapidly on Sunday and become a major hurricane by Monday, with sustained wind speeds of at least 111 miles per hour (179 km per hour), forecasters said.

Its center will move between Bermuda and the Bahamas on Tuesday and Wednesday, and approach the southeastern US coast on Thursday, the NHC said in an advisory.

Florence's precise path remained uncertain on Saturday, but the NHC said the "risk of direct impact" somewhere between Florida and North Carolina was increasing.

North Carolina Governor Roy Cooper declared a state of emergency on Friday and urged residents to prepare for Florence's arrival. Authorities in Florida and South Carolina said they were closely monitoring the storm.

Florence, which was at hurricane strength earlier this week before weakening to a tropical storm, had maximum sustained winds of 65 mph (105 kph) on Saturday.

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