The storm was moving northwest at 10 miles per hour. "We're still going to have a Category 4 storm surge".
"The deepest water will occur along the immediate coast in areas of onshore winds, where the surge will be accompanied by large and destructive waves. Surge-related flooding can vary greatly over short distances", the advisory said.
Once the rain hits the coast, it will accumulate very quickly, causing some flash flooding and eventually likely overwhelming streams and rivers in the areas that get the most. Numerous flight cancellations and delays Thursday involved arrivals or departures at airports in Florence's path.
Mayor Joe Benson said the storm will batter Carolina Beach through two high-tide periods.
According to forecasters, the center of Florence is expected to hit North Carolina's southern coast Friday, then drift southwest before moving inland on Saturday.
But what forecasters are keeping an eye on, in particular, is the forward motion of the storm.
Nevertheless, torrential rain will be moving ashore Thursday, continuing into Friday, and dumping one or perhaps even two feet of rain in some areas.
Richard Deakin, head of insurance sales for CoreLogic in New Zealand said: "Whilst our thoughts are obviously very firmly focused on those facing the danger and potential aftermath of Hurricane Florence, it's important to note that U.S. weather events could impact the premiums that New Zealanders pay on their home insurance". That makes sense since the category of a storm is generally determined by its maximum sustained winds; but, researchers have found, the vast majority of deaths (nearly 90%) from hurricanes, tropical storms, or tropical depressions between 1963 and 2012 were attributable to "storm surge, rainfall flooding, high surf, and deaths just offshore".
Over 1 million residents of coastal states including North Carolina and SC were ordered to evacuate as of Thursday afternoon, ahead of the expected landfall of Hurricane Florence on Friday.
Just as Hurricane Florence closes in on the Southeast, the area covered by hurricane-force winds has doubled - meaning far more people will get blasted with winds 74 miles per hour or greater.
The storm's eye was about 145 miles southeast of Wilmington as of 11 a.m., the briefing said.
"This storm will bring destruction", North Carolina Governor Roy Cooper said. As the recovery from past storms continues in many rural towns, the next storm is about to strike.
That will be in addition to a storm surge that could reach nine feet.
"It truly is really about the whole size of this storm", National Hurricane Center Director Ken Graham said. The axis of heaviest rain may shift further south or west, but the extreme rainfall is going to happen.
"It has moved in", said Jordan Baker, a meteorologist with the National Weather Service Office in Wilmington. "We're about to be in the thick of it".
Needham, who drove all night from Miami to North Myrtle Beach, South Carolina, to watch and record the storm surge from the relative safety of a parking garage, said the storm surge had "already gobbled up the beach" there.