Florence Evening Update for Tuesday 11 September 2018

First some advice.  Don’t freak out over any one computer model forecast, and be skeptical about folks who show you dramatic graphics and talk about tracks while not discussing the official National Hurricane Center forecast all that much.  Tropical Cyclone Forecasting is specialized, and understanding all of the nuances of track models takes a lot of experience.  Most of what you read here is either an interpretation of or derived from NHC forecasts using my active research work on natural hazard damage models.  While I work on forecast models of various kinds, and have a deep understanding of numerical weather models, for the most part I leave that end of the business to the folks who do it every day.  Why are my discussions often less dramatic than other sources?  Probably because my income doesn’t depend on hits, viewers, or selling you stuff 🙂  But let’s start with the obligatory dramatic satellite picture anyway …

As usual, lets will look at the track, the likely impacts on that track, followed by the implications of those impacts in both economic and human terms.  This is a bit of a tough forecast situation.  There is a high pressure ridge to the north of the storm that is currently guiding it towards North Carolina.  That should control the motion for the next two days (until Thursday).  But then things get a bit less clear.  This morning, most indications were that a “weakness” in that ridge would cause the winds steering the storm to slow down or even stop as it makes landfall over North Carolina, drifting for a couple of days, then begin to move northestward, dumping a bunch of rain in the process.  Today, however, the dramatic ECMWF model runs making the rounds in social media show the storm “bouncing” off the high and moving SW,  showing Florence heading south and perhaps even hitting again as far south as Georgia.  Most models, however, just show some kind of jog  offshore rather than just inshore as was the case this morning. So the big picture is more or less the same Here’s some of the track models as of 4pm this afternoon (ECMWF isn’t shown for licensing reasons) …

So what does all that mean?  Well, let’s see what the experts have to say.  Here is the 5pm NHC forecast track.  I added in the 5am track from this morning in yellow for comparison.  Not so different, huh?  From their forecast discussion, “there remains no significant change to the previous forecast track or reasoning.” 

So what’s the bottom line? No major developments. The areas under watches/warnings/evacuations are not changed. The damage estimates are about the same – somewhere around $14 Billion in direct damages, flood damages highly dependent on exactly where Florence stalls out and how much rain gets dumped.  Folks in the immediate path of this thing should get out of the way.  IF the storm does do the stop and turn shown above, that’s good: it will be weaker, and cause less damage.  If it follows the ECMWF scenario, it will almost certainly not be in very good shape as storms don’t like to run in to walls of air and get shove at a 90 degree angle … so there is still no need to panic, just keep watching the official forecasts, smile (and don’t make any sudden moves) at folks who are freaking out and latching on to every weird variation in this complex situation, overreacting to pretty pictures, and stay cool …

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