Very scary storm surge possible in SC/NC, which is why evacuations have already begun. Here's the latest post by Jeff Masters from Wunderground, one of the world's foremost experts on hurricanes. It's chilling. He says that if we get a Cat 4 landfalling hurricane in SC/NC there would likely be 15-20 foot storm surges based on surge models and historical data - catastrophic isn't a strong enough word for what would happen. A cat 4 landfalling solely in NC would be the first time in recorded history; there have only ever been 3 Cat 4's north of GA - Hugo (1989 which hit Charleston), Gracie (1959, which hit Edisto SC) and Hazel (1954, which hit the SC/NC border).
Expect a Storm Surge of 15 - 20 Feet in a Landfalling Category 4 Storm in the Carolinas
Dr. Jeff Masters · September 10, 2018, 1:48 PM EDT
Landfalling Category 4 hurricanes are rare in the mainland U.S., with just 24 such landfalls since 1851—an average of one every seven years. (Category 5 landfalls are rarer still, with just three on record). All but three of these 27 landfalls by Cat4s and Cat5s have occurred south of South Carolina’s latitude; thus, Florence will be in very select company if it manages to make landfall at Category 4 strength in North or South Carolina.
If Florence hits the coast of North or South Carolina as a Category 3 or stronger hurricane, we should expect to see record storm surge heights, with a 15 – 20’ surge very possible, according to two experts I communicated with today. Dr. Robert Young, Professor of Coastal Geology at Western Carolina University, says that “the track of Hurricane Florence, combined with its expected size and strength at landfall and the unique coastal geomorphology of the region, is likely to result in a record storm surge along portions of the warning area.” And according to storm surge expert Dr. Hal Needham, “we could definitely see a 20+ foot storm surge/storm tide in the Carolinas. Even if Florence weakens a bit in the time right before landfall, the surge heights correlate better with the pre-landfall winds than the winds at landfall.”
It’s a good thing that landfalls by such strong hurricanes are rare along the South Carolina and North Carolina coast, since this coastline is extremely vulnerable to high storm surges. Two of these three historical Carolina Category 4 hurricanes generated a storm tide of 18 - 20 feet: Hugo of 1989 and Hazel of 1954. The other storm--Gracie of 1959--did not (it hit at low tide, significantly reducing the coastal flooding). The storm tide is the combination of the storm surge and the normal lunar tide, measured in height above sea level. The National Hurricane Center uses the terminology “height above ground level” when discussing the storm tide, meaning the height the surge plus tide gets above the normal high tide mark.
The high vulnerability of this coastline is because the continental shelf extends out more than 50 miles from shore, creating a large region of shallow water less than 150 feet deep just offshore that forces storm surge waters to pile up to staggering heights. (See our storm surge basics page for more information).
WU's storm surge inundation maps for the U.S. coast, computed using NOAA’s SLOSH model, tell a frightening story. Depending on where its center makes landfall, a mid-strength Category 4 hurricane with 145 mph winds hitting at high tide, in a worst-case scenario, can generate a storm tide in excess of twenty feet above ground level along the entire coast of South Carolina, and along most of the coast of southern North Carolina from the South Carolina border to Morehead City. Many locations could see a higher surge, of up to 27 feet. And a Category 5 storm is much worse: a theoretical peak storm tide of 33 feet is predicted by the SLOSH model for the Intracoastal Waterway north of Myrtle Beach, South Carolina. These peak surges occur over a 10 - 40 mile stretch of coast where the right eyewall makes landfall. If Florence were to make landfall near Wilmington, NC, for example, the highest surges would extend northeastward to around Jacksonville, NC.
According to HURDAT, the official Atlantic hurricane database, these are the three Category 4 hurricanes that have hit the U.S. coast north of Georgia, since record keeping began in 1851:
https://www.wunderground.com/cat6/E...0-Feet-Landfalling-Category-4-Storm-Carolinas