Florence's large size - tropical storm force winds extend 170 miles from the center in all directions - means its fury will arrive long before the center of the storm comes ashore, Graham said.
"Heed the warnings", said Byard, adding there was "well over $20 billion" in FEMA's disaster relief fund.
"Get out of its way, don't play games with it, it's a big one, maybe as big as they've seen", Trump said.
Forecasters with The Washington Post's Capital Weather Gang are now saying Florence is a Category 4 storm that could bring very risky winds, flash flooding and power outages.
For many of those under evacuation orders, getting out of harm's way has proved difficult, as airlines cancelled flights and motorists had a hard time finding gas. Catastrophic flooding and destructive winds are becoming very likely in the eastern Carolinas.
The storm is now expected to make landfall in the lower Outer Banks of North Carolina early Friday morning or possibly stay in the ocean before making a shift to the left toward SC.More news: Google execs bemoan Trump election in 2016
President Trump says the Federal Emergency Management Agency and first responders are poised to help - but he also warned people to get out of the storm's path. The power is going to be off for weeks.
New projections indicate the now-Category 3 hurricane will move slightly southeast, with landfall expected between Wilmington and Morehead City, North Carolina.
The governors of Virginia, Maryland, North Carolina and SC have also declared a state of emergency for their states in preparation for Florence's arrival.
The eastbound lanes of several major highways have been shut down to allow traffic to flow inland, but the exodus was slow along roads jammed with outward-bound vehicles.
A storm surge watch is in effect for Edisto Beach, SC, to South Santee River, SC, and for north of Duck, NC, to the North Carolina/Virginia border.More news: Florence pours on the rain in the Carolinas, swelling rivers
"If I need to evacuate I can go to my son's house", Sparks said as he carted a load of water bottles to his auto.
"This morning I drove around for an hour looking for gas in Cary".
"What happens is that we rescue some people and then we find out there are still more who need it", Outlaw said.
Small said the precautions have worked in previous hurricanes, but he said he remained wary of the flooding potential from the storm with the same name as his town. "It's sort of like having 33 weather stations out in the middle of the ocean", said flight director Richard Henning. "We have everything. We're ready". "If you are on the coast, there is still time to get out safely".
With South Carolina's beach towns more in the bull's-eye because of the shifting forecast, OH vacationers Chris and Nicole Roland put off their departure from North Myrtle Beach to get the maximum amount of time on the sand. All three states ordered mass evacuations along the coast.
And an unusual combination of other weather systems that are likely to stall Florence when it hits the Carolinas, allowing it to sit for days and dump huge amounts of rain.More news: Won't Run for a Second Term, Says Iraq Prime Minister
The NHC said Helene was weakening, however, and posed no danger to land.