Packing winds of up to 220 km/h (140 mph) late Monday, Florence was expected to further strengthen and become "an extremely unsafe major hurricane" by the time in makes landfall in the Carolinas on Thursday, the National Hurricane Center (NHC) said in a 21:00 UTC update.
The governor of South Carolina, Henry McMaster, ordered the mandatory evacuation of the state's entire 187-mile coastline at noon on Tuesday.
The 1st effects were already being seen on barrier islands Monday as unsafe rip currents and seawater flowed over the state highway.
More than 30,000 people have accepted the invitation to the tongue-in-cheek event, with a further 72,000 interested, according to a public Facebook post.
Florence is now moving west at around 13 miles per hour. People living well inland should prepare to lose power and anticipate flooding and other hazards, he warned.
"From eight o'clock 'til two we were slammed", said Johnson, who sold scores of bags of sand over the weekend, saving just a few to barricade the store's own doors.
"We do not want to risk one SC life in this hurricane", Governor Henry McMaster told a news conference.
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Hurricane Florence has been quickly strengthening Monday and is on route to severely impact the Carolinas at the end of the week.
Storm surge could be as high as 6 to 12 feet from Cape Fear to Cape Lookout on North Carolina's southeast coast. The storm is expected to make landfall along the North Carolina coast, possibly as a Category 4 storm, overnight Thursday into Friday.
Preparations intensified up and down the densely populated coast.
The National Hurricane Center says a new report from an Air Force Reserve Unit hurricane hunter aircraft indicates that Hurricane Florence's top sustained winds have decreased slightly to 130 miles per hour (215 kph), with higher gusts.
Florence is forecast to dump up to 40 inches (one meter) of rain in some areas after it makes landfall in North and SC.
Meanwhile, Pentagon spokesman, Col. Robert Manning said, "Northern Command is spending an advanced team to the emergency operations center in Raleigh, North Carolina Monday to conduct an assessment and coordinate with federal and state partners". "But we're not going to gamble with the lives of the people of SC".
North Carolina Governor Roy Cooper's office said Florence is already being felt along the state's coast, with large sea swells resulting in life-threatening rip currents and surf.
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The ocean waters that Florence is travelling over are about 2.7 degrees (1.5 degrees Celsius) warmer than normal, McNoldy said. Almost 1000 prisoners in SC will not be moved from their cells, despite a mandatory evacuation order in the area.
Evacuations were happening along the coast of North and South Carolina, and the projected landfall was expected between Charleston, South Carolina, and Norfolk, Virginia.
"But I'm staying", she said.
Aides say they are applying lessons from last year's spate of storms to an expected repeat season of destruction.
An evacuation order from Virginia governor Ralph Northam applies to about 245,000 people, including parts of the Hampton Roads area and Eastern Shore.
The Atlantic hurricane season officially began June 1, but cooler water and higher wind shear - winds moving at different speeds and directions - early in the season are less than ideal for tropical systems to gain and maintain strength.
Mike Herring with Frank's Ice Company unloads another pallet of ice as people buy supplies at The Home Depot on Monday in Wilmington, N.C.
There have only been 26 category 4 hurricanes to ever make landfall in the us since 1850.
1.5m to evacuate as Hurricane Florence approaches US
Nathan Deal says the state "is mobilizing all available resources to ensure public safety ahead of Hurricane Florence ". In a news release Wednesday, Gov.