"All interests from SC into the Mid-Atlantic region should ensure they have their hurricane plan in place and follow any advice given by local officials", the Hurricane Center said.
The storm, which fell from category four to category three on the five-step Saffir-Simpson scale, is expected to strengthen despite it weakening on Wednesday. "If this blows at 120 mph for four hours, ... you lose a shingle every two minutes, and all of the sudden, you've lost your whole roof after four hours", Myers said.
Hurricanes are massive storm systems that form over warm ocean waters and move toward land.
Trump declared states of emergency for North and SC and Virginia, opening the way for federal aid.
As of 11 p.m. EST, the storm was centered 280 miles east southeast of Wilmington, North Carolina, and was moving northwest at 17 mph.
Duke Energy warned that Florence could cut off power to anywhere from 1 million to 3 million customers in North and SC, potentially leaving them without electricity for several weeks, said spokeswoman Grace Rountree. Rather than pushing up toward western Virginia, the storm's center is now predicted to move across eastern SC on Friday night and Saturday.
Moreover, high tides around noon and midnight these next few days will make the storm surges even worse, Samson said.
Evacuation orders for low-lying areas were issued Monday and continued Tuesday.
"These enormous waves are produced by being trapped along with very strong winds moving in the same direction [of] the storm's motion", the agency said.
South Carolina Governor Henry McMaster has ordered the mandatory evacuation of one million coastal residents while neighboring North Carolina ordered an evacuation of the Outer Banks, barrier islands that are a popular tourist destination, and parts of coastal Dare County. "People who live in New Bern have experienced hurricanes before, but it has been a long time since we have experienced something like this".
In the first report of storm-related fatalities, a mother and infant died after a tree fell on a house in Wilmington, North Carolina, according to local police. The port in Charleston, South Carolina, though, was suspending operations from Thursday through Saturday and possibly on Sunday.
The pivot in the forecasted track of Florence led Georgia's governor to declare a state of emergency for all 159 counties, home to 10.5 million people.
Jeff Byard, FEMA associate administrator for the Office of Response and Recovery, called Florence "a very risky storm".
She said it will become a "major flooding event". "It goes well inland".