Fierce winds and massive waves are expected to lash the coasts of North and SC and Virginia even before Florence makes landfall by early Friday, bringing a storm surge as much as 13 feet (4 meters), the National Hurricane Center in Miami warned.
Packing maximum sustained winds of 140 miles per hour (225 km per hour), the storm ranked as a Category 4 on the five-step Saffir-Simpson hurricane scale and was expected to grow stronger and larger over the next few days, the NHC said.
It is then forecast to close in on North or SC on Thursday, hitting a stretch of coastline that is vulnerable to rising sea levels due to climate change. "Please be prepared, be careful and be SAFE!" the president tweeted.
South Carolina's governor ordered the evacuation of the state's entire coastline on Tuesday and predicted that a million people would flee as major roads reverse directions. Rainfall could reach 40 inches in isolated locations of coastal North Carolina.
The storm's first effects were already apparent on barrier islands as unsafe rip currents hit beaches and seawater flowed over the road.
Two years ago, more than a million poultry birds died when floodwaters from Hurricane Matthew covered areas across central and eastern North Carolina.
Airlines including American, Southwest, Delta and JetBlue are letting affected passengers change travel plans without the usual fees.
More than 20 inches (51 cm) of rainfall are possible across eastern North Carolina, said Don Keeney, senior agricultural meteorologist for weather forecaster Radiant Solutions.
People living well inland should prepare to lose power and endure flooding and other hazards, he warned.
"This one really scares me", Graham said.
A warm ocean is the fuel that powers hurricanes, and this area of the ocean is seeing temperatures peak near 30C, hurricane specialist Eric Blake wrote. It looks like it will slow down and perhaps even stall near the coast of the Carolinas.
"Based on the current weather forecast related to Hurricane Florence, the Boston College at Wake Forest football game originally scheduled for 7:30 p.m. Thursday night (Sept. 13) in Winston-Salem, North Carolina, has been moved to 5:30 p.m", said the ACC's release on Tuesday.
In addition to Florence, the Atlantic Ocean now has two other strong storms.
Hurricane Isaac is expected to lose strength as it reaches the Caribbean, and Helene, much farther out to sea, may veer northwards into the open ocean as the 2018 hurricane season reaches its peak. But the storm is expected to strengthen again over the next day or so.
Preparations for Florence were intensifying up and down the densely populated east coast.
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.
Still, the hog industry disputes the idea that there's much environmental risk from the waste lagoons, said Andy Curliss, Chief Executive Officer of the North Carolina Pork Council.
I am very familiar with the Outer Banks of North Carolina, having vacationed there since 1991.
Duke coach David Cutcliffe says the team will leave Durham on Thursday instead of its typical Friday departure because it's "our best opportunity to get out".