"This will likely be the storm of a lifetime for portions of the Carolina coast", the National Weather Service in Wilmington, N.C., said, "and that's saying a lot given the impacts we've seen from hurricanes Diana, Hugo, Fran, Bonnie, Floyd, and Matthew".
"This is going to be a Mike Tyson punch to the Carolina coast", said Jeff Byard, the associate administrator for response and recovery at the Federal Emergency Management Agency (FEMA).
At 2:00 pm (1800 GMT), the eye of the storm was 435 miles (700 kms) southeast of Wilmington, North Carolina, moving northwest at 16 mph (26 kph).
National Hurricane Center Director Ken Graham said damaging winds and rain could begin hitting the coast late Thursday, pushing a storm surge that could reach 13 feet in places.
"I ask all Georgians to join me in praying for the safety of our people and all those in the path of Hurricane Florence", Deal said.
The storm is also expected to trigger "life-threatening, catastrophic flash flooding & significant river flooding over portions of the Carolinas and Mid-Atlantic states from late this week into early next week", forecasters wrote on Twitter Tuesday.
"He was thinking of coming here until this morning, and now he asked me if I wanted to come up there", he said.
Hurricane Florence, growing in size despite its weakening winds, churned ever closer to the U.S. East Coast on Wednesday as evacuations expanded south from the Carolinas into Georgia to counter the threat of deadly high seas and calamitous floods.
"We have to be careful we're not asking them to come back to Beaufort County through a storm", he said.
"We hope to have something left when we get home", she said.
"Florence is intensifying", said North Carolina's Governor Roy Cooper, adding: "This storm is strong, and its gettings stronger". "If you are on the coast, there is still time to get out safely".
The category four hurricane is set to bring with it heavy rains and winds of up to 225 kilometres per hour.
Duke Energy has around 4 million customers in North and SC, and says it could take several weeks to restore the electricity.
The prison, home to nearly 1,000 prisoners and up to 119 staff, was ordered to stay put even during an initial mandatory evacuation for surrounding Jasper County.