Landfall is expected late Thursday or early Friday, and the National Hurricane Center fears the storm "will slow considerably or stall, leading to a prolonged and exceptionally heavy and risky rainfall event Friday-Sunday".
The National Weather Service said Hurricane Florence will bring a life-threatening storm surge and rainfall to parts of the Carolinas and Mid-Atlantic states.
"Heed the warnings", Mr Byard said.
Since Tuesday, forecasts have shifted the storm track towards the south and southwest after it reaches the coast, which could increase the storm's severity in coastal SC through Myrtle Beach and Charleston and even into parts of Georgia.
A mother and baby were killed when a tree fell on their home in Wilmington, North Carolina.
Up to 1.7 million people are under voluntary or mandatory evacuation orders, and coastal residents were frantically boarding up homes and businesses and hitting the road on Wednesday as the storm approached. In North Carolina, Cooper says, "2,800 soldiers will be on active duty, joined by even more on standby".
Hurricane Florence's potentially devastating winds are generating enormous waves as high as 83 feet as it continues to make its way toward the East Coast and insurers predict it will become the costliest such storm to ever hit the continental U.S.
The percentage of customers who may be affected by power outages following Hurricane Florence. All three states ordered mass evacuations along the coast. Governors of those states have already declared states of emergency, as have the governors of Virginia and Maryland.
South Carolina Gov. Henry McMaster said, "This hurricane is bringing more rain than any other hurricane", according to SCETV.
The storm, which fell from category four to category three on the five-step Saffir-Simpson scale, is expected to strengthen despite it weakening on Wednesday.
"I encourage Georgians to be prepared for the inland effects of the storm as well as the ensuing storm surge in coastal areas", he said.
"The Charleston area now is expected to see at least 1-2 inches of rain over the next several days". "I'm a little bit scared right now", she said, "but I have my iPad and I'm watching Netflix".
On Wednesday morning, Florence was extending hurricane-force winds outward up to 70 miles from its center, with tropical-storm-force winds up to 175 miles outward.
Forecasters anxious the storm's damage will be all the worse if it lingers on the coast.
However, forecasters warned the widening storm, and its likelihood of lingering along the coast for several days, raises the risk of surging ocean water and torrential rain.
As Florence drew near, President Donald Trump tweeted that Fema and first responders are "supplied and ready", and he disputed the official conclusion that almost 3,000 people died in Puerto Rico, claiming the figure was a Democratic plot to make him look bad.