Until yesterday, Cline said, the hurricane had been traveling through a pressure trough that generated a lot of shear - essentially, winds in the upper levels of the atmosphere traveling at different speeds than winds at lower levels.
When it reaches the coastline, it could sit around for days, unloading life-threatening storm surge, unsafe winds and flooding rain. At more than 470 miles across, Florence is 56% wider than the typical Atlantic hurricane.
President Donald Trump has insisted that the government is "absolutely, totally prepared" for the arrival of the hurricane.
On Tuesday, Washington D.C.'s mayor, Muriel Bowser, declared a state of emergency in the District ahead of the hurricane, effective immediately.
The Coast Guard started positioning rescue helicopters, equipment and people to best respond to the storm several days ago, and brought in some assistance from other parts of the country, service officials said.
The Pentagon sent a small team of Defense Department personnel to an emergency operations center in Raleigh, N.C., on Monday to carry out an assessment and coordinate with state officials, said Col. Rob Manning, a Pentagon spokesman.
Henry McMaster lifted the mandatory evacuation for Hurricane Florence in Beaufort, Jasper and Colleton counties Wednesday, Beaufort County schools will remain closed Wednesday.
The massive storm is threatening the East Coast of the United States with an expected landfall late Thursday.
He said that North Carolinians should obey evacuation orders, as Florence is expected to affect millions in both North and SC.
McMaster has already declared a state of emergency in SC and asked President Donald Trump for a federal declaration ahead of the storm, which intensified Monday to a potentially catastrophic Category 4 hurricane with maximum sustained winds near 130 miles per hour (195 kph). But, it's the water, not the wind, that has the potential to make the storm so deadly, experts say. The storm's track is now heading toward the North Carolina city of Jacksonville, about 50 miles north of Wilmington.
A tropical storm warning, indicating the expectation of conditions below hurricane-strength winds, is in effect for coastal areas north of the Virginia border to Cape Charles Light, Va., and in Chesapeake Bay, south of New Point Comfort, Va.
While many coastal residents heeded mandatory evacuation orders, others boarded up homes and businesses and chose to courageous the storm, which is forecast to trigger severe flash flooding as it dumps as many as three feet (almost a meter) of rain in some areas. We do have a pretty old facility here, so we're hoping it doesn't blow away in the storm. "What is flooding going to do to our home, our city?"
Hurricane Florence is now a massive Category 4 hurricane.
Florence's projected path includes half a dozen nuclear power plants, pits holding coal-ash and other industrial waste, and numerous hog farms that store animal waste in massive open-air lagoons.
Virginia Gov. Ralph Northam's evacuation order applies to about 245,000 people, including parts of the Hampton Roads area and Eastern Shore.