The hurricane center warned that the swells are likely to cause "life-threatening" surf and current conditions.
The turbulent storm was last spotted 710 miles southeast of Bermuda moving west at 6mph.
The storm was still on a path to strike the Carolinas, potentially southern North Carolina, as a major hurricane at about 2 a.m Friday, according to the latest forecast from the hurricane center.
Florence's top wind speeds were still hovering at about 130 miles per hour on Tuesday, making Florence a Category 4 hurricane.
"This storm is too powerful and its path is too uncertain to take any chances", he said. He said North Carolina is "bracing for a hard hit" in what forecasters say will be a statewide event.
In South Carolina alone, more than 1 million residents and tourists are expected to flee from coastal areas, Gov. Henry McMaster said Monday, vowing that state officials "are not going to gamble" with people's lives.
Even if Florence avoids a direct hit on the East Coast, it will likely come very close, resulting in risky surf, beach erosion, and the potential for coastal flooding. At this point, its exact landfall location is very hard to determine as Florence will eventually make a NW and then north turn.
Officials in the Carolinas warned residents to prepare and to brace for impact.
A Hurricane Warning has been issued from South Santee River, S.C., to Duck, N.C., and the Albemarle and Pamlico Sounds while a Tropical Storm Watch was issued from north of the North Carolina/Virginia border to Cape Charles Light, Va., and for the Chesapeake Bay south of New Point Comfort.
Generators, bottled water and snacks were flying off the shelves of area retailers over the weekend as forecasts called for higher chances that Hurricane Florence could hit the area. The state's emergency management agency said it is "preparing for the possibility of a large-scale disaster".
Tropical Storm Florence is becoming a "better organized" weather system that will likely strengthen into a hurricane late Saturday, weather forecasters said. Hurricanes Helene and Isaac are not expected to hit the USA mainland.
Tropical-storm-force winds could reach the coastline as early as Wednesday night, at which point all outdoor preparations should be completed.
Tropical Depression Nine formed 1755 miles east of the Windward Islands Friday. It is expected to accelerate during the next 36 hours and head into the eastern Caribbean Sea by Thursday.
The latest models on Saturday show that it's becoming less likely the storm will veer north and miss the mainland US entirely.