The tropical storm could begin to batter the southeastern U.S. by late on Wednesday, with Florence possibly making landfall around the Carolinas on Thursday or Friday.
"While it's still too early to know the storm's path, we know we have to be prepared", Gov. Cooper said.
Swells generated by Florence could cause risky rip currents and coastal flooding on Saturday in areas including coastal DE and New Jersey, the National Weather Service said.
The odds of a Southeast coast landfall from Florence continue to increase. As of 5 p.m., it was centered about 720 miles (1,160 kilometers) southeast of Bermuda, moving west at 7 mph (11 kmh). North Carolina Sergeant Chris Knox told NPR, "This allows our farmers to gather their crops, and get these crops out ahead of the storm". Three states, including South Carolina, North Carolina, and Virginia have already declared states of emergency in preparation for the storm's impact.
Florence's precise path remained uncertain on Sunday, but the NHC said the "risk of direct impact" somewhere between Florida and North Carolina was increasing.
Gov. Roy Cooper announced the declaration in a news release Friday evening as the storm neared Bermuda.
Some forecast models showed Florence slamming into land by late next week, while others indicated the storm would curve away from the shore.
Florence became the first major hurricane of the 2018 Atlantic season this past Wednesday, reaching Category 4 status with maximum sustained winds peaking at 130 miles per hour.
"Make your plans now", South Carolina Governor Henry McMaster urged residents during a Sunday afternoon news conference.
Adm. Christopher Grady said in a statement that the decision was based on Florence's current track, which indicates the area could see strong sustained winds and storm surges.
Drawing energy from the warm water, it could be a fearsome Category 4 with winds of 130 miles per hour (209 kph) or more by Tuesday, the National Hurricane Center said. Florence will be an extremely risky Category 4 hurricane as it moves over western waters of the Atlantic Ocean.
"It's important to remember the cone of uncertainty covers the entire SC coast, meaning landfall in SC is still a possibilty", Quagliariello said.
A tropical storm warning and hurricane watch are in effect for the Cabo Verde islands of Santiago, Fogo, and Brava.
Isaac will be near the Lesser Antilles later this week and could bring impacts to parts of the Caribbean Islands during this time frame.