Florence's centre was expected to move over the Atlantic Ocean between the Bahamas and Bermuda on Tuesday and Wednesday before approaching North and SC on Thursday.
North and SC and Virginia ordered mass evacuations along the coast. It is expected to intensify to near Category 5 status as it slows over very warm ocean water near North and SC.
"You are talking about the entire ocean level rising up as a storm of this size makes landfall", Barnes said.
There are fears Florence could match the devastating impact of Hurricane Hazel in 1954, which brought 130mph winds to North Carolina, destroying 15,000 buildings and killing 19 people.
Henry McMaster lifted the mandatory evacuation for Hurricane Florence in Beaufort, Jasper and Colleton counties Wednesday, Beaufort County schools will remain closed Wednesday.
The 29-year-old said he already went through 2011's Hurricane Irene, and cited flooding as the worst threat.
In the six decades since, many thousands of people have moved to the coast. Charles Mullen, 81, a longtime resident of Hatteras Island, North Carolina, said he had ridden out many storms and that most locals were planning to stay unless Florence took aim at Hatteras.
"You may see a smaller footprint from the operations staff, but. that is what is needed at the time, at this time in the state", Byard said. "With the size and the intensity and the current forecast track, it's a risky time for people in North Carolina with regard to this storm". "All you have to do is look up at your ceiling, and think about 12 feet (of water)".
Florence's projected path includes half a dozen nuclear power plants, pits holding coal-ash and other industrial waste, and numerous hog farms that store animal waste in huge lagoons.
"Get to a safe place now or by Thursday morning", he said.
Evacuation orders have also been issued. Ryan Moser, a spokesman for the North Carolina-based electricity company Duke Energy, said operators would begin shutting down nuclear plants at least two hours before hurricane-force winds arrive. Hurricane force winds extend 40 miles from Florence's eye and tropical storm force winds extend 150 miles.
Streams of cars clogged roads leading away from the coast of North and SC on Tuesday as residents began fleeing ahead of the arrival of Hurricane Florence, a powerful Category 4 storm barreling towards the eastern U.S. states.