Florence has weakened considerably from where it was just a couple of days ago when it had reached category four intensity. Strong upper level winds and cooler sea surface temps have taken a toll on the structure of the storm and this has allowed it to do something very important and critical to the final outcome of its track. Move west.
Since Florence does not fill up as much of the atmosphere due to the collapse of deep thunderstorms or convection, it is being steered more by the lower to mid-level flow which is more east to west. This means that the storm will gain much more longitude (move more west) than latitude (north). At this point, the longer Florence remains in this weakened, sheared state, the higher the stakes in terms of where it ends up in about a week.
Unfortunately, it looks as though Florence will again become a strong hurricane over the very warm water of the western Atlantic and by the time it does so, it would have tracked far enough south of any weakness in the high pressure (trough) to make the connection and turn north. The irony is glaring: a weaker Florence now means an increased threat for a major hurricane landfall along the Southeast or Mid-Atlantic later. This is not unheard of, however. In 1992, hurricane Andrew underwent a very similar evolution and ended up as the 3rd category five to ever strike the United States. I am not suggesting that Florence will become a cat-5 or make landfall in south Florida, but the overall plot line seems eerily familiar.
I generally look at 3 camps of global models: GFS, UKMET and ECMWF. I like to see what the operational or deterministic runs show and then take a peak at the “what if” scenarios outlined in what we call the ensembles or multiple runs of the same models using different variables to show different outcomes. It’s fairly easy to understand what to look for. The more spread in the overall model guidance, the more uncertainty there is and vice versa.
So far, the GFS remains the good news messenger with a track that would spare the U.S. coast a direct hit. Even its ensembles are mostly well offshore.
On the other hand, the UKMET and ECMWF operational models both paint an ugly picture for the Southeast coast, essentially bringing Florence ashore as a strong hurricane. Right now, the “exactly where” part is irrelevant since we’re talking six to seven days away. The point is, those two global models and most of their ensembles strongly suggest a landfall somewhere. As such, the official NHC track forecast has Florence positioned at 30N and 70W in 120 hours. From there, it either turns more north and we all breathe a sigh of relief or the intensity of preparing for a major hurricane landfall begins to ramp up in to overdrive for a stretch of coastline.
I simply do not know how this will play out but the trends are not positive right now, especially considering how warm the water is off the East Coast and the strong, solid high pressure area that is keeping summer very much alive from the Northeast down to Florida.
The bottom line is that Florence poses a threat of some level of impact to the U.S. coast (Bermuda too) and we will notice this over the weekend as swells begin to roll in; delighting surfers I am sure. This will be the first signs of a possible major hurricane heading our way. I think we will know definitively about whether Florence turns north in time or not within the next 24 hours. After that, we can begin to focus more on exactly where it could end up.
92L and 93L
There is also growing concern that we see development from invest areas 92L and 93L as they track across the now warm waters of the Main Development Region. We have several days to monitor the progress but I think it goes without saying that we need to keep a close eye on 92L as models suggest it could impact the Lesser Antilles directly.
Olivia and Hawaii
As if all the activity in the Atlantic weren’t enough to keep up with, we also have what is currently hurricane Olivia churning in the east-central Pacific. Here too we may have the threat of direct impacts for Hawaii but this time, coming in from the north and east. The official forecast from the CPHC indicates that Olivia will weaken below hurricane strength with time. Here too, we have a few days to watch and see how the steering and intensity patterns evolve with Olivia. Obviously, any major rain threat for Hawaii is concerning, much less a tropical cyclone heading their way. I will keep up with the latest on this situation as well.
I will address all of these topics more and more in subsequent updates to the blog and within my video discussions which I will also post here at least once per day.
M. Sudduth 6:20 AM ET September 7