WGN’s Tom Skilling provides update on Hurricane Florence

Hurricane Florence, bearing down on the Carolina coast and expected to make landfall late Thursday or early Friday -- its winds and high surf will arrive as much as a day earlier -- is predicted to carry fearsome Cat 4 and borderline Cat 5 winds.

This may take it down to a Cat 3 storm, but the change may be more academic than relevant in real terms. And if it does make landfall as a Cat 4 intensity storm, with winds topping 131 mph, it will become only the fourth storm to do so north from South Carolina's latitude since records of U.S. hurricane landfalls began in 1851.

Florence rainfall forecast out of the NWS's Weather Prediction Center (WPC)

Whether a Cat 3 or a Cat 4 at landfall, what is being predicted here is a life-threatening, truly fearsome storm -- and on so many different levels. Florence's story won't end with landfall. The rain production of any hurricane is beyond description. I remember encountering Hurricane Donna out in New Jersey as a boy. I have never BEFORE OR SINCE seen it rain that hard! I remember the scenes of devastation which followed. Entire root systems of 150-year-old oak trees were uprooted as these trees collapsed under the assault of Donna's winds. And THAT storm was nowhere near as strong as what's about to hit the Carolina coastline.

Predictions that Florence will slow to a crawl and linger for days with its torrential downpours is raising the specter of Hurricane Harvey which hit Houston, Texas with what can only be described as "Biblical" rains last year --50 inches or more. Florence may become the "Harvey of 2018!" say some of my colleagues -- and they're right. Rains for Florence may exceed 20 inches in the hardest hit locations -- and this is ONLY an early projection. Stay tuned!

Among the many truly fearsome aspects Hurricane Florence poses to the Carolina coast and beyond is a potentially catastrophic storm surge, which some experts say could reach as much as 15 to 20 feet.

"Storm surge" refers to the dome of water which hurricanes sweep up and over the coastlines they impact. Beyond the strength of the storm and the timing of its landfall relative to local high tides -- even the stage of the lunar cycle -- the storm surge a hurricane produces depends a good deal on layout of the coastal geography and the waters surrounding, what's referred to as the "geomorphology" of the coast.

Tropical expert Dr. Jeff Masters of Weather Underground lays out a potentially catastrophic storm surge scenario for Florence and the Carolinas pointing out the devastating nature of the storm surges produced by two of the three CAT 4 strength hurricanes which have hit the coastline north of Georgia at high tide since 1851: Hurricane Hazel on October 15, 1954 and Hurricane Hugo on Sept. 22, 1989. Their maximum storm surges were 15 to 20 feet and 18 to 20 feet, respectively. Ponder those numbers for a moment!

Storm surges such as those would be the equivalent in Chicago of lifting the level of Lake Michigan 15 to 20 feet, while bombarding the shoreline with 20-plus foot waves on top of all that water. And of course there would be 130 to 140+ mph sustained winds, driving rains and even the potential of tornadoes to boot. Quite simply, for those coastal areas, what's being predicted is the literal onset of meteorological and oceanographic hell, which is why its essential those in the area follow evacuation orders--especially on barrier islands, many of which were formed by past hurricanes--and GET OUT! NO ONE should be there because there's no way for any human to possibly deal with that.

Masters explains the structure of the Carolina coastline is unique along the Carolinas and how it drives the potential for huge storm surges there.

The continental shelf, he explains, extends out more than 50 miles from the coast and the waters there are comparatively shallow, i.e. 150 feet or less. This means the incoming winds of a hurricane like Florence, can pile water up with comparative ease. The result can be gargantuan storm surges. Dr. Jeff Masters' entire post can be read here.

See the latest advisories from the National Hurricane Center here and here.