The storm is now expected to make landfall in the lower Outer Banks of North Carolina early Friday morning or possibly stay in the ocean before making a shift to the left toward SC.
The Federal Emergency Management Agency warned that storm surge watches and warnings are in effect Wednesday for the entire North Carolina coast and parts of SC.
In Holden Beach, North Carolina, in the storm's path, longtime residents were busy securing their homes and possessions.
Steady streams of vehicles full of people and belongings flowed inland Tuesday as Gov. Roy Cooper tried to convince everyone on North Carolina's coast to flee.
"This one really scares me", National Hurricane Center Director Ken Graham said. "Everyone was sold out", she said. "It's one of those situations where you're going to get heavy rain, catastrophic, life-threatening storm surge, and also the winds".
About 300,000 people have been evacuated from South Carolina, McMaster said. It was a potentially catastrophic Category 4 storm but was expected to keep drawing energy from the warm water and intensify to near Category 5, which means winds of 157 miles per hour (253 kph) or higher. Officials worry that as many as 1,000 of the town's 6,300 residents are staying in the town, which is less than 5 feet above sea level. It is the most unsafe of three tropical systems in the Atlantic.
There is quite of bit of certainty in the tracking forecast, replied Brock when asked by the president whether Florence could veer off course away from coastal areas.
Hurricane Florence: Residents told to 'heed the warnings'
The storm's surge , the rise in sea water above normally dry land at the coast, could reach up to 13 feet at peak. LATER NEXT WEEK: The remnants of Hurricane Florence could bring some heavy rain to the D.C. region by next week.
Hurricane Florence Tracking South
ET, Florence was 530 miles southeast of Cape Fear, N.C., moving west-northwest at 17 mph, the National Hurricane Center says . Now a Category 4 storm , it's possible that it could strengthen even more as it moves swiftly through the Atlantic Ocean.
5 photos of Hurricane Florence
Up to 1.7 million people have been ordered to evacuate across South Carolina , North Carolina and Virginia. As of Tuesday, more than 1.7 million people in the Carolinas and Virginia were warned to clear out.
A Category 4 storm is capable of ripping roofs off houses, snapping or uprooting most trees, bringing lasting power outages and making areas uninhabitable for weeks or months. It's going to destroy infrastructure.
One trusted computer model, the European simulation, predicted more than 45 inches (115 centimeters) in parts of North Carolina.
Forecasters said parts of North Carolina could get 20 inches (50 centimeters) of rain, if not more, with as much as 10 inches (25 centimeters) elsewhere in the state and in Virginia, parts of Maryland and Washington, D.C. "We know we can't play around with this", said Jennifer Oosterwyk, who owns the Sugar Britches boutique on Holden Beach and lives in nearby Wilmington.
Duke Energy spokesman Ryan Mosier said operators would begin shutting down nuclear plants at least two hours before hurricane-force winds arrive.
The trend is "exceptionally bad news", said University of Miami hurricane researcher Brian McNoldy, since it "smears a landfall out over hundreds of miles of coastline, most notably the storm surge". Typically, local governments in the state make the call on evacuations.
"The biggest hazard that we are anxious about is storm surge", he said. "Many more are being urged to evacuate at-risk areas voluntarily".