The NHC said Florence is forecast to strengthen over the weekend, becoming a hurricane again by Sunday. The storm is expected to take a track that will move west-southwest and eventually curve toward a possible landfall in North or SC.
It was moving west close to 7 mph, about 720 miles from Bermuda, the National Hurricane Center said.
Computer-model forecasts generally project the storm to make landfall between northern SC and North Carolina's Outer Banks as a Category 4 on Thursday, although shifts in the track are possible and storm impacts will expand great distances beyond where landfall occurs. NHC added that the risk of direct impact from the storm along the U.S. East Coast over the next week has increased, but it is too soon to determine location, magnitude and timing of the impact.
The storm was expected to cause life-threatening surf and rip currents along the United States east coast this weekend.
Tropical Storm Florence turned into a hurricane Sunday morning and swirled toward the USA for what forecasters said could be a direct hit on the Southeast toward the end of the week.
Meanwhile, the two other tropical storms in the Atlantic - Florence and Helen - are expected to become hurricanes today. One of the primary concerns with this system is the inland flooding threat.
The hurricane center says Category 3 storms can bring "devastating" damage.
The center also said that Hurricane Isaac, much farther out to sea, has become the 5th named hurricane of the 2018 Atlantic season.
"Now is the time for your family also to prepare and stay tuned for more updates", South Carolina Gov. Henry McMaster said.More news: Obama: 'Our democracy depends' on people voting
The storm's maximum sustained winds remain near 85 km/h with higher gusts and it is moving west near 15 km/h.
Florence's immediate threat for residents includes large ocean swells, unsafe rip currents and coastal flooding.
In South Carolina, McMaster ordered the state's entire coastline evacuated starting at noon Tuesday.
Roy Cooper declared a state of emergency Friday, just a day after Tropical Storm Florence was downgraded from a Category 1 hurricane.
Experts say the East Coast should prepare for a blow by the middle of the week as the hurricane rapidly intensifies.
Regardless of exact forecast tracks, significant impacts for parts of the Carolinas and Virginia are likely.
Walsh says we could see adjustments to the models throughout the next few days that may bring severe weather to SC including "tremendous amounts of rainfall" starting Friday along the coast.
Officials in North Carolina were already preparing for impact.
"While it's still too early to know the storm's path, we know we have to be prepared", Gov. Cooper said. Florence has been moving more toward the west and slightly northwest, potentially making direct landfall coming in from the east.