3pm, Sunday, September 9, 2018
There has been no fundamental change in the thinking of Florence.
Watching the satellite imagery suggests a hurricane that has begun the process of strengthening rapidly.
There will be two major impacts. The initial hit on the coastline… with wind damage and coastal flooding from the storm surge. This looks like it will be somewhere between Wilmington, NC and Cape Hatteras… but areas south to Myrtle Beach and north to Virginia Beach still cannot be ruled out as the initial hit.
This will probably happen on Thursday… leaning toward afternoon or night. But 12-24 hours of wiggle room should be considered.
Likewise, it will very likely be a Category 3, 4, or possibly a 5 at coastal impact (aka landfall). Everything we understand about hurricane intensity indicates a rapid strengthening should take place between Sunday afternoon and Tuesday afternoon. I would not get too hung up on small fluctuations in intensity, say bouncing back and forth between a 3 and 4 or a 4 and 5, as there is nothing to suggest a miraculous weakening would happen before landfall.
While the strongest winds are concentrated in the wall of clouds and rain around the eye of the hurricane (the eyewall), damaging winds usually are found at least a few dozen miles away from the center, so please do not focus solely on the point of impact.
After the initial landfall, the storm will turn north through central North Carolina and into Virginia for Friday and into the weekend (Sep 14-16). While still having some 40-50 mph winds by then, the devastating wind impacts from the storm will probably subside by Saturday. Nonetheless, at least scattered tree damage would probably happen in central NC (Raleigh, Greensboro), and into southern Virginia (Roanoke to Richmond)… and perhaps farther north toward Staunton and Fredericksburg.
This leads to the second impact, which often gets lost in the runup to landfall… inland flooding.
There are very worrisome indications that the storm center will stall somewhere over Virginia or North Carolina Saturday and Sunday and then slowly drift back toward the coast… or perhaps back out to sea. However, that is still 7-10 days out. And the storm will continue to weaken as it drifts, so the wind threat will be long gone.
But as mentioned above, the storm is not a point, the rain from these post-landfalling systems extends far out from the center, and the rainfall pattern is NOT symmetric around the center. So there is much uncertainty about precise rainfall estimates next weekend. Having said that… it could mean historic flooding for Virginia. Flooding would first hit streams and creeks Friday and Saturday…. and then into the state’s larger rivers Sunday and into the following week. Is it definite? No. But there is a very serious flooding risk developing for Virginia, and it should be taken seriously.
Specific to Virginia… how much rain? Over the course of 3 days (Friday through Sunday), 5-10 inches is a conservative estimate… probably highest in the areas west of I-95 and toward the West Virginia state line. More disturbing is that some of our more reliable computer simulations suggest 12-16 inches of rain covering several dozen square miles in the western part of the state. Imagine encircling an area that includes Danville, Lynchburg, Charlottesville, Staunton, Covington, Roanoke, and Blacksburg. This would be devastating to the James River (all the way to Richmond) and the Roanoke/Staunton Rivers. But the Shenandoah (and ultimately the Potomac), York, and Rappahannock Rivers would also be at risk.
It is my hope that in the next day or two, there is some trend in the simulations away from this phenomenal rain idea for Virginia, so there is still another day or two to refine the forecasts. But these are the kind of figures that make me think about the James River flooding from Agnes in ’72 and Camille in ’69.
Below is a map of Virginia River basins. Know where the heavy rain is falling, ’cause this is where the water ends up.
I have also enclosed one rainfall totals simulation below (from the European Centre for Medium Range Weather Forecasting), indicating the total amount of rain between now and 8am Monday morning (17th). Do not focus on the specific amounts in small numerical print. The broad area of very heavy (purple) rain is what is most troubling. This particular simulation was from 8am Sunday, Sept 9. A quick review of the data shows that 80-90% of that rain would come from Florence. Again… it is one simulation, but it does underscore that there is a legitimate risk of a once-in-a-generation flooding scenario for Virginia.
On a personal level, I will not be able to spend as much time as I would like on the analyses of the storm in the coming few days. Find a trusted meteorological source in your area. I encourage you to listen to his or her words and the tone in his or her voice. Do not get caught up or distracted by flashy television graphics or fanciful wording from news anchors. Do not fall for click bait on the web. Some trusted media colleagues that I have known for a long time… John Bernier, Jim Duncan, Andrew Freiden, Brent Watts, Will Stafford, Jeff Lawson, Aubrey Urbanowicz, Travis Koshko. And the National Weather Service offices in Blacksburg, Wakefield, and Sterling are staffed by good people who live in their communities and know their areas well. Follow them online.