The hurricane could also produce heavy and excessive rainfall - up to 40 inches in isolated areas in the Carolinas and anywhere between 6 to 12 inches elsewhere in the Appalachians and Mid-Atlantic region.
With Hurricane Florence bearing down on the East Coast, is it time for a radical rethink on what it means to be prepared?
As of 2 p.m. Wednesday, the Category 4 storm was about 435 miles southeast of Wilmington, N.C., and moving northwest at about 16 mph.
The National Weather Service said 5.25 million people live in areas under hurricane warnings or watches, and 4.9 million live in places covered by tropical storm warnings or watches.
On Wednesday morning, the president urged those in the path of Florence to "get out of its way".
A tropical storm watch is in effect for north of the North Carolina/Virginia border to Cape Charles Light, VA, and for Chesapeake Bay south of New Point Comfort. "It's a big one".
Timing: When Will Hurricane Florence Strike?
"This is going to be a Mike Tyson punch to the Carolina coast", he warned.
The East Coast isn't the only area facing the brunt of a storm. She said it will become a "major flooding event".
With South Carolina's beach towns more in the bull's-eye because of the shifting forecast, OH vacationers Chris and Nicole Roland put off their departure from North Myrtle Beach to get the maximum amount of time on the sand.