"You could have a delay when power is out, bridges could be out, roads could be flooded and you won't be able to deliver goods and materials for reconstruction", says Dorf, "or for that matter, clean water and food and other important supplies like batteries". "Persons located within these areas should take all necessary actions to protect life and property from rising water and the potential for other risky conditions", the hurricane center briefing said. "Don't plan to leave once the winds and rains start". The governor added that a million or more people could be evacuated before the storm makes landfall.
Normally when we talk about the potential for hurricane damage, we talk about the impact of storm surges and high winds - both of which are, to be sure, incredibly unsafe in their own right. Currently, the hurricane-force winds extend outward 80 miles from the center and tropical storm-force winds extend almost 200 miles from the eye.
The storm's maximum sustained winds were clocked at 175kmph late on Wednesday, down from a peak of 225kmph a day earlier, before it was downgraded to a Category 3 and then a Category 2.
More than 5.4 million people live in areas under hurricane warnings or watches on the US East Coast, according to the NWS, and another four million people were under a tropical storm watch.
Officials in several states have declared states of emergency, including in the Carolinas, Georgia, Virginia and Maryland, where coastal areas are still recovering from summer storms.
The centre of Florence is expected to hit North Carolina's southern coast on Friday (local time), then drift south-west before moving inland on Saturday, enough time to drop as much as one metre of rain in places, according to the National Hurricane Centre (NHC). The storm was moving northwest at 10 miles per hour.
Although the storm is approaching the USA coastline as a Category 2 hurricane after weakening from a Category 4 storm, that doesn't mean the storm will be gentle.
Body surfer Andrew Vanotteren, of Savannah, Georgia, crashes into waves in the surf bolstered by the incoming Hurricane Florence on the south beach of Tybee Island, Georgia. That forecast area also includes part of southwest Virginia.
About 300,000 people have been evacuated from South Carolina, McMaster said.
For the first time, researchers have calculated the impact of climate change on a hurricane before the storm is over.
People in North Carolina and SC have the daytime hours Thursday to complete their final preparations to ride out or escape the storm.
More than 1,200 US airline flights scheduled for Thursday and Friday have been canceled, according to the flight-tracking service FlightAware. The Charleston area is under a storm surge watch.
North Carolina has had this problem before.
"Floodwaters may enter numerous structures, and some may become uninhabitable or washed away", the Weather Service warned.
Even if Hurricane Florence's category weakens, or if the storm no longer maintains its hurricane status, the amount of rain can still be biblical. Most were scheduled for Thursday and Friday. Hurricanes that fall into categories 1 or 2 are still considered unsafe, the center says.
The zone where these intense winds occur will be narrow and they will last just a few hours, but the effects will probably be severe, similar to a tornado.
"Catastrophic damage will occur: A high percentage of framed homes will be destroyed, with total roof failure and wall collapse".