Mandatory evacuation orders have been issued for the coasts of South Carolina, North Carolina and Virginia, and states of emergency have been declared there as well as Maryland and the District of Columbia.
And the storm surge, which could be as much as 12 feet in some areas, will be on top of sea level rise from climate change.
Cooper added: "The waves and the wind this storm may bring is nothing like you've ever seen".
Florence is projected to make landfall as a Category 4 storm in the early morning hours of Friday.
Winds: Florence is now a Category 4 storm with maximum sustained winds of 130 miles per hour.
Florence is now around 800 miles from Cape Fear, North Carolina, moving at 16mph with winds of 130mph. With little wind shear to pull the storm apart, hurricane-strength winds have been expanding to 40 miles from the eye of the storm, and tropical-storm-force winds 150 miles from the center. The wind and rain will continue to ramp up during the day Thursday with hurricane force gusts (74 mph+) arriving Thursday evening.
South Carolina's governor ordered the state's entire coastline to be evacuated starting at noon Tuesday and predicted that one million people would flee.
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Hurricane Florence has the potential to bring catastrophic flooding to areas of the eastern U.S. already soaked by heavy rain.
President Donald Trump on Tuesday said the federal government would spare no expense in responding to the likely damage from Hurricane Florence, which is forecast to slam the Carolina coast later this week.
The NHC warned they're likely to cause "life-threatening surf and rip current conditions".
"All indications are that the storm will slow down and just crawl or meander over the inland sections and the coastal Piedmont", Weather Channel hurricane expert Bryan Norcross said. This could lead to massive flooding in many of North Carolina's inlets.
Hurricane Florence is barreling toward the southeastern United States because of the so-called "atmospheric brick wall", the high-pressure system that's guiding it there, forecasters report.
This is one considered by the US National Hurricane Centre (NHC) as having sustained wind speeds of more than 157mph.
So far, American Airlines flights have not been canceled due to the storm, but it is bracing for the worst and letting travelers potentially affected by the storm change their travel dates without paying change fees, normally around $200 plus a difference in fare, as per CNBC.