With weather forecasters calling the storm "life threatening", Cooper said officials are watching three main issues - storm surge along the coastline, strong winds which could be heavier than any the state has experienced in recent years, and inland flooding and heavy rains.
Florence is so wide that a life-threatening storm surge was being pushed 300 miles (485 kilometres) ahead of its eye, and so wet that a swath from SC to OH and Pennsylvania could get deluged.
Virginia Governor Ralph Northam ordered a mandatory evacuation for about 245,000 residents of low-lying coastal areas, while some coastal counties in North Carolina have done the same. However, tropical storm force winds of 40 miles per hour could develop as early as Thursday morning.
For many people, the challenge could be finding a safe refuge.
Authorities are warning about Florence's potential to unleash prolonged torrential rains and life-threatening floods, down trees, knock out electricity and submerge entire communities - especially if it slows to a crawl and lingers inland for several days, just as Hurricane Harvey stalled over Texas in 2017.
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.More news: Cliff collapse at tourist beach on Greece's Zakynthos island injures seven
Although the focus on where Hurricane Florence makes landfall is drawing lots of attention, another looming threat could be the worst impact of this monster storm: disastrous, deadly flooding from days of relentless rain. But the firm warns that Tropical Storm Isaac, which formed in the Atlantic Ocean on Saturday, is right behind Florence.
At 2pm Tuesday afternoon, Florence was located 845 miles (1360km) southeast of Cape Fear, North Carolina.
Florence was about 405 miles south of Bermuda and its center was forecast to move between Bermuda and the Bahamas through Wednesday, before approaching the coast of North Carolina or SC on Thursday, the National Hurricane Center (NHC) said in its 8:00 am (1200 GMT) advisory.
It's unclear if some other games in the Carolinas or Virginia could be affected by the storm.
The same thing happened a year ago with Hurricane Harvey.
Preparations for Florence were intensifying up and down the densely populated east coast.
Meanwhile, Energy Secretary Rick Perry says the US electricity sector has been well prepared for Hurricane Florence even as hundreds of thousands of homes lose power in the storm. The risk of flash flooding is 20%, or moderate, for the eastern third of North Carolina. "If you are given an evacuation order, please comply immediately before roads get clogged and chaos commences". "This is the craziest one".
It's outer band can be seen at the top of the above photo in the red box. She grew up on the island chain, and says this will be only the second time she has evacuated. And out here we're so fragile.
'We are well-prepared to support our neighbors during this event, ' Livingston said.