Maximum gusts were measured at 130 miles per hour.
Enough rain could fall to break North Carolina's record for a tropical storm - 24 inches - set near Wilmington during Hurricane Floyd in 1999, said Greg Carbin, chief of forecast operations at the Weather Service's national prediction center.
Mr Graham said the Pamlico and Neuse rivers in North Carolina will see their flows "reversed" as storm surges push water back inland.
Locally, here in Northeast Florida and Southeast Georgia, the storm has generated a moderate risk of rip currents. As of Wednesday evening, the surf was already picking up. Heavy rains were forecast to extend into the Appalachians, affecting parts of Alabama, Tennessee, Kentucky and West Virginia.
A day later, he issued a dire warning to anyone who is flouting the evacuation order, telling them that "you're putting your life in danger" and that Wednesday "is the last day to travel".
"We will experience power outages, we will have infrastructure damaged, there will be homes damaged, and there will be debris on the roads", said Jeff Byard, an official from the Federal Emergency Management Agency. "It's time for our citizens to be a part of the team".
"It does look a bit similar to Harvey in a sense that it goes roaring into shore and then comes to a screeching stop", said MIT meteorology professor and hurricane expert Kerry Emanuel.
"We have to be careful we're not asking them to come back to Beaufort County through a storm", he said. "This is not just a coastal event".
"Finally I ask all Georgians to join me in praying for the safety of our people and all those in the path of Hurricane Florence".
"The water could overtake some of these barrier islands and keep on going. Now it might be time for the exam", Baxley said late in the morning. But authorities warned it will still be an extremely risky hurricane.
North Carolina Governor Roy Cooper warned that "disaster is at the doorstep", and "tens of thousands" of buildings may be flooded.
In a videotaped message from the White House, President Donald Trump said the government is fully prepared for Florence but urged people to "get out of its way". All seven of North Carolina's ferry routes were shut down.
Hurricane Florence is expected to hit as Category 3 or Category 4 storm, and could drop three feet of rain. The first tropical storm-force winds of at least 39 miles per hour (63 kph) were forecast to hit the coast on Thursday.