Florence is already causing power outages, with the U.S. Energy Department reporting that almost 400,000 customers have lost power in North and SC.
The barrier island of Emerald Isle is under water, with ocean waves rolling in over a six-foot storm surge and crashing into homes.
Forecasters say "it can not be emphasized enough that the most serious hazard associated with slow-moving Florence is extremely heavy rainfall, which will cause disastrous flooding that will be spreading inland".
The cone of probability for Hurricane Florence as of 11:00 p.m. EDT, Sept. 13, 2018.
Corps staff worked with Army officials to review dams at Fort Bragg in North Carolina and Fort Jackson in SC to "ensure any effects of Florence on those dams are mitigated", said Ray Alexander, the Corps' inter-agency services chief.
The news came more than 10 hours after the storm began punishing the coastal area with sustained hurricane-force winds, the hurricane center said. Authorities have advised people, however, to move to higher levels in their homes while they wait to be rescued.
It will likely come on shore Friday near Wilmington, North Carolina.
According to Colleen Roberts, a spokeswoman for the city, 150 people were waiting to be rescued Friday morning after about 200 were rescued overnight.
The National Hurricane Center says the Neuse River near the city is recording more than 10 feet (3.05 meters) of inundation.
"WE ARE COMING TO GET YOU", the city of New Bern tweeted around 2 a.m. The non-emergency call center for Hurricane Florence is 919-996-2999.
Parts of the mid-Atlantic can also expect heavy rains from what is left of Florence well into next week.
Meteorologist Ryan Maue of weathermodels.com said Florence could dump a staggering 18 trillion gallons of rain over a week on North Carolina, South Carolinas, Virginia, Georgia, Tennessee, Kentucky and Maryland.
"This is an absolute life-threatening scenario". Emerald Isle is about 84 miles (135 kilometers) north of Wilmington.
More than 3,000 inmates at North Carolina prisons and juvenile detention centers were moved out of the storm's path. We will have tropical storm force winds and rain and storm surge continues to be our main concern with extreme flooding.
As Hurricane Florence makes landfall along the coast of North Carolina with winds raging at more than 90 miles per hour, shelters across that state and others are preparing for whatever damage comes next.
Emergency response teams have been "fully pre-positioned" to help local governments and companies like utilities cope with the damage Florence will leave, Long said - but the storm has to leave. Flash flooding, downed trees and power outages will be possible in these regions early next week before Florence finally departs the East Coast on Wednesday or Thursday. The few cars out on a main street in Wilmington had to swerve to avoid fallen trees, metal debris and power lines. A storm surge warning is in effect for South Santee River South Carolina to Duck North Carolina.