National Hurricane Center Director Ken Graham warned that Florence is expected to linger once onshore, downing trees, knocking out electricity and causing widespread flooding.
"Florence is expected to produce total rainfall accumulations of 15 to 20 inches with isolated maxima to 30 inches near Florence's track over portions of North Carolina, Virginia, and northern SC through Saturday".
"On the five-level Saffir-Simpson hurricane wind scale Florence is a Category 4, meaning "catastrophic damage" can occur".
At 11 p.m. EDT, the storm's center was located about 465 miles (750 kilometers) south-southeast of Bermuda and about 1,085 miles (1745 kilometers) east-southeast of Cape Fear, North Carolina.
Crews also prepared 16 nuclear reactors in the three-state region for the storm.
Rain could reach as much as 10 inches elsewhere in North Carolina, Virginia, parts of Maryland and Washington, D.C.
"This will have a storm surge in the 20-foot range", Myers said.
"The water could overtake some of these barrier islands and keep on going". "All you have to do is look up at your ceiling, and think about 12 feet (of water)".
Governors of several states including North and SC have also waived certain trucking and transportation regulations to help prep for the storm - and be ready to take quick action once the worst it over. Trump tweeted, adding: "WE are here for you".
As he issued a mandatory evacuation order for the coastal region Monday afternoon, South Carolina Gov. Henry McMaster didn't mince words.
SC lifted mandatory evacuation orders for three coastal counties as the storm's path became more certain.
According to AccuWeather there is a potential scenario where Florence will stall or significantly reduce its speed which could prolong the effects of damaging winds, storm surge flooding and beach erosion.
AccuWeather Vice President of Forecasting and Graphics Operations Marshall Moss said: "There's never been a storm like Florence".
The large and powerful hurricane prompted evacuation orders in North and SC and Virginia - all of which have already declared states of emergency. "This rainfall may produce life-threatening flash flooding".
Coastal areas need to be concerned of storm surge, heavy winds, and potentially tornadoes, while Porter also stressed there is a strong possibility of the storm "stalling out for days" once it moves inland.
Besides the power of this storm, the other major concern is its speed.
Michael Kennedy, an engineer at Boeing, said he planned to leave on Tuesday for his parents' home in Atlanta, Georgia.
"Florence is moving toward the west near 13 miles per hour". Information gathered Tuesday by a hurricane-hunting aircraft suggests it will intensify again as it nears the coast, approaching the 157 miles per hour (253 kph) threshold for a worst-case Category 5 scenario.
That doesn't quite measure up to the 25 trillion gallons Harvey dropped on Texas and Louisiana a year ago.
Further east, forecasters are watching Hurricane Helene and Tropical Storm Isaac in the Atlantic, and a patch of showers in the western Caribbean, which has a 30 percent chance of becoming a cyclone in the next 2 days. But the storm is expected to strengthen again over the next day or so.
On the other hand, companies that help people ride out a storm, or clean up afterward, are having an exceptional week.
Urging residents to evacuate, he said Florence was "the strongest storm to target the Carolinas and this part of the country in decades". Even scarier: It could get more violent as it gets closer to the Carolinas.