If Hurricane Florence's forecast track holds, it almost certainly will endanger lives, set off devastating floods, destroy coastal properties, yet again inundate the bankrupt National Flood Insurance Program, and redefine the beaches along vulnerable barrier islands.
And holding to the forecast would also make Florence somewhat distinctive — because most of the time, hurricanes do not behave quite as forecasters expect they will. Right now, predictions of how the storm is moving are slightly better than average, but if it didn't spring some surprises, that, itself, would be a surprise.
The National Hurricane Center said Tuesday afternoon that Florence was a Category 4, with peak winds of 130 mph, about 850 miles east-southeast of the Carolina coast and due to make landfall there by Friday morning. As always, it advised everyone to pay attention to the entire forecast cone, not just that tidy line indicating the storm center, since Florence's effects will be widespread.
Meteorologists caution that hurricane forecasting eventually bumps against the limits of science. Even within 24 hours of landfall, it's impossible to say precisely where the eye will cross a shore, how powerful it will be, and what will happen when it travels inland, dropping what could be lots of rain — or not much at all — in the Mid-Atlantic region.
"Despite incredible improvements in tropical cyclone track forecast errors and skill, it is well accepted that making perfect forecasts will never happen," National Hurricane Center experts Chris Landsea and John Cangialosi wrote in a recent paper.
On Tuesday, forecasters were saying that Florence is unlikely to have major effects on the Philadelphia region. However, precisely where the eye of a hurricane makes landfall can make worlds of differences in terms of impacts, as Andrew, in 1992, proved when it came ashore just south of Miami.
In terms of following predicted paths, Florence has been a bit better behaved than most, said Brian Tang, hurricane specialist at SUNY-Albany. Within 48 hours, the National Hurricane Center tracks have missed the marks by 70 miles, he said; the average in recent years is 80 miles.
"The mechanisms steering Florence are fairly large-scale and stagnant, lending to a forecast track that doesn't have too much spread or uncertainty," said Tang. That makes a Carolinas landfall "very likely."
But where, exactly, along the nearly 500 miles of Atlantic coast that border North and South Carolina?
If it came ashore near, say, Cape Fear on the southern coast of North Carolina, it likely would mean a devastating storm surge across the Outer Banks. That's because the upper-right quadrant of a hurricane, where winds are from the east and northeast, typically is the surge-maker.
If it landed farther north, above Cape Hatteras, it could have significant surge impacts all the way to the Delaware and Maryland beaches.When Andrew made landfall in 1992 as a Category 5 with winds around 160 mph, it buzz-sawed through Homestead, Fla., like a tornado. Had it entered 25 miles to the north at Miami, it might well have become the most expensive — and perhaps one of the deadliest — in U.S. history.
Florence probably won't be a Category 5, but it might arrive as a Category 4. Unfortunately, however, nailing changes in intensity has been just about as elusive as predicting directional changes.
The hurricane center said Tuesday that it's possible Florence will slow down near the coast on Thursday. Shallower water would mean a decreased supply of warm water to fuel the hurricane, weakening it. Also, Florence could encounter shearing winds in the upper atmosphere that would take away some of its strength before landfall, the center said.
Intensity is governed by "multiple-scale processes, including the large-scale ones, like wind shear … and ocean temperature, and the small-scale ones," such as thunderstorms within the hurricane, said Chia-Ying Lee, scientist at the International Research Institute for Climate and Society at Columbia University. "These processes are not fully understood; the smaller-scale features are not well observed, and are chaotic in nature."
How fast the entire storm is moving — not just its internal wind speeds — is another key factor that isn't entirely knowable. Whether Florence weakens or maintains its strength, if it slows down along the coast, that would increase the potential for a prolonged storm-surge disaster, said Steve DiMartino, a meteorologist with the Weather Concierge forecasting service.
Finally, where Florence goes after landfall is a major imponderable for the Mid-Atlantic region.
"My biggest fear is that it will stall out," said Stephen Strader, a disaster specialist at Villanova University. Worst-case scenario: a disaster similar to the deadly Texas rainfalls wrung out by Hurricane Harvey after landfall last year.
"Flooding may ultimately be the big story," agreed Tang. DiMartino said heavy rain bands associated with Florence's remnants could end up dousing areas well to the north of North Carolina, including the Philadelphia region.
He also said that the lower air pressure associated with the remnants might work in tandem with an area of high pressure to the north to generate prolonged periods of strong winds from the east that could threaten power lines and cause coastal flooding at the Shore; winds are caused when air moves from areas of higher to lower pressure.