Losses from Florence could be on par with those from two previous storms: Hurricane Hazel, which ravaged North Carolina in 1954, causing $15 billion in losses, and Hurricane Hugo in 1989, which caused $20 billion, according to a report from risk modeling firm RMS on Tuesday.
"But despite that, bad things can happen when you are talking about a storm this size", he added.
It is unclear exactly how many people fled, but more than 1.7 million people in the Carolinas and Virginia were warned to clear out.
The result could be what the Houston area saw during Hurricane Harvey just over a year ago - catastrophic inland flooding that could swamp homes, businesses, fields and industrial sites. North Carolina corrections officials said more than 3,000 people were relocated from adult prisons and juvenile centres in the path of Florence, and more than 300 county prisoners were transferred to state facilities.
At 2 p.m., the storm was centered 845 miles (1,360 km) southeast of Cape Fear, North Carolina, moving at 17 mph (28 kph).
"Do you want to get hit with a train or do you want to get hit with a cement truck?" said Jeff Byard, an administrator with the Federal Emergency Management Agency. Many major roads and arteries have reversed traffic flow to help residents evacuate quickly.
"If I need to evacuate I can go to my son's house", Sparks said as he carted a load of water bottles to his vehicle.
A buoy off the North Carolina coast recorded waves almost 30ft high as Florence churned toward shore.
Florence interrupted her stay on North Carolina's Outer Banks.
"Against my better judgment, due to emotionalism, I evacuated", he said.
"I do worry though about people here because many didn't prepare, you know, because originally they didn't think it was going to be so bad here", Sparks said.
Trojniar said she and her husband were packing up belongings and planned to stack sandbags around their single-floor home in Wilmington's Landfall neighborhood near the ocean before checking into a hotel to ride out the storm.
"We hope to have something left when we get home", she said. "I was in the same house and it stood fine".
"People need to leave now before they can't", North Carolina Gov. Roy Cooper said.
Lt. Col. Lindy White, an Oklahoma National Guard spokeswoman, said officials from East Coast states are expected to request additional assistance in the days to come.
In Virginia, 245,000 coastal residents were ordered to evacuate, including from the Eastern Shore.
A hurricane warning was issued for South Santee River, SC, north to Duck, NC, and the Albemarle and Pamlico Sounds.
Authorities in New Bern, a town of about 30,000 people that dates to the early 18th century, said more than 100 people had to be rescued from floods.
Elsewhere in the Atlantic basin, Tropical Storm Isaac will strike the islands of the Lesser Antilles, with Guadeloupe, Dominica and Martinique under a tropical storm warning.