Sorry this is a long post, but lots of stuff to cover! For many places it takes a minimum of 36 hours (and for some coastal metro areas, much longer) from the time you decide you want to launch an evacuation to the time everybody that is going to leave is out of the danger zone. But of course that’s not 36 hours before landfall – you want people out of the way before conditions become hazardous for travel. For a big storm, that can be up to 24 hours before actual landfall. Add in safety margins to account for delays, factor in time of day (doing an announcement at midnight doesn’t help since most folks won’t see it for another 6 hours or so), and we are now up to 4 days prior to landfall for having to make the big decision. Although Florence has slowed down her forward speed this morning, on the current National Hurricane Forecast official track, we are likely less than 5 days before landfall for a major category 3 hurricane (and certainly less than that for impacts like high winds and waves along the shore). So we’re now entering the time frame where emergency managers have to begin making hard decisions. Here’s what they have to work with …
First and most important, there is the official NHC track. It is critical, as they preach, not to focus on the track line because storms are not points but big blobs, so here is the current forecast with the damage swath depicted using my Haetta/TC model used to show areas that will be impacted over the next five days assuming the storm follows this track.
Now, NHC are the experts at this sort of thing – but at five days it would not be surprising to see the actual landfall location as much as 200 miles either side of this track. That means a direct hit is possible from Charleston SC to the DelMarVa penensula (with the band of severe impacts extending 100 miles to the right/north, and 60 miles to the left/south, of that spot). But as with most things it’s more complicated than that. The average doesn’t tell you much about the bias. For a storm in this location, and error to the right (north) is more likely than an error to the south. Is that true for Florence? Well NHC talks about this kind of thing in their forecast discussions, and we can look at the forecast model tracks to see where the biases might be …
Most of the models, and most of the models doing well on this storm, say somewhere on the Grand Strand of SC (Myrtle Beach area) up through Chesapeake Bay, most likely to be the WIlmington NC or Outer Banks.
So we’ve got a handle on where, but how strong? That’s a hard question. Again, NHC is forecasting rapid intensification, with good reason. The storm is showing signs of better organization, and is moving towards the warm waters of the Gulf Stream, a great energy source. Intensity is a very complex subject, but let’s go with NHC’s forecast (even if it may be a bit on the strong side).
Bottom line for decision makers: Category 3 hurricane likely to make landfall Friday, with damaging impacts starting late Thursday. Landfall is probably going to be somewhere on the North Carolina coast, meaning the area of damaging impacts is more than likely going to be somewhere from Charleston to the DelMarVa Penensula, but the most likely area of severe impacts is the North Carolina coast. Georgia is on the outside edge and trending better. North of DelMarVa (eg New Jersey) is not in the worry zone – for now – but that may change later when we figure out what the thing is going to do if it stalls at or near the North Carolina coast as the long range models are implying. On the present NHC forecast, Florence is on track to cause over 15 Billion dollars in damage. Using an extended forecast, I would not surprised to see Florence top out at over $25 Billion in impacts, putting it in the top 10 most expensive hurricane to make US landfall.
So what do you personally do? If you live in coastal SC, NC, VA, MD, or De, you should have your hurricane plan ready to execute. It is likely that emergency managers will begin recommending actions today, early tomorrow at the latest. Unlike some past storms on the East Coast the last few years, this is a hard core straight in off the water storm more like a Hugo or Andrew. Take it seriously. Georgia, Hilton Head (my “home turf”) Keep an eye and be alert, but this one is very likely to be north of us, and aside from some waves, not a big deal. But the next day will tell.