Looking at the models this morning, it’s time to do a big update on this system. At the moment, anyone who says they know where this system is headed is someone you should probably not listen to, even if they end up being right. The five-day outlook is completely wide open, and that’s the emphasis of this post.

The one visible trend in the models: The more west the path, the stronger the system. Not surprising for one since 99L will have to cross the Florida peninsula to enter the Gulf – at least, probably. The models truly are wide open. Speaking of models, here we go – and I’m posting several this time because it’s important not to focus on a single model or even a single spaghetti plot:


I’m starting with this spag from the SFWMD because I think it makes the uncertainty a little easier to visualize. You can see that some models recurve the system into the Atlantic with possibly no landfall, or landfall and affecting only the Bahamas. Some models take it across the Florida peninsula, or even across the Keys and into the Gulf. And in the Gulf, models range from Pensacola to Texas (not so easy to see in this spag, but bear with me).

This is the primary message of this post: the uncertainty of where 99L will be. The secondary message is the intensity forecast, so we’ll look at that before I return to more spag plots.


This is the current intensity forecast. I should like to note that the previous forecast had a couple of models forecasting 99L to reach Category 3 Major Hurricane status. Granted that they were outliers, it’s still notable that the forecast models have been and continue to be all over the place, from TD to TS to Cat1+.

So this is the secondary message of this post: The uncertainty in the strength of the system.

It is critical to discount any person or organization who, at this point, claims to be sure where this system is going and how strong it will be. It is also critical to consider the possibility that this system may end up anywhere from the Bahamas to Texas and that it may be anything from a tropical depression to a hurricane, even possibly a major hurricane. Thus, it is critical not to panic about this system, but to prepare to make preparations just in case, and to monitor this system over the next few days.

A note specifically for my Florida Panhandle friends: There is a moderate chance at this time that we will see anything from rain to a full tropical system in a few days. At this specific time, the models are trending in a split to our east or west, however, that’s around five days out, and there is huge uncertainty with this system. So as above: monitor this system. I will definitely be making daily updates for the foreseeable future of this system.

So, to continue a discussion of the wide variance in the models, here’s another spag:


After seeing the first spag, I believe this shows better the full range of models at the moment. Note that a lot of models show recurvature of the system into the Atlantic; all the way to making landfall in Florida. Some models show the system moving south of Florida and impacting AL/LA. So, again, there is extreme uncertainty for the path this system will take.

Finally, here’s the GFS ensemble. This is one model that does a number of runs based on slightly different starting locations and parameters. Basically, it can be hard to get a fix on a developing system, so this tries to account for that by running the model multiple times with slightly different parameters. When you see such a wide variety of solutions, it helps emphasize the uncertainty in the forecast:


Remember, this is one model, just with different starting parameters. As you can see, it’s all over the place. Thus, the path uncertainty is very very large at this time. The white line is the official GFS forecast track. It shows up as just one of the options in the other spag plots. So consider what it might look like if I had an image with ensembles from all the models.

So with all that caution and emphasis on the uncertainty out of the way, I want to end with one image from Mike’s Weather Page on Facebook from yesterday, showing the difference a day makes in one forecast model. These are two possible scenarios, and I think it’s important to present this; but present it with the disclaimer that as per the rest of this post: everything is hugely uncertain. The system will nearly certainly not be at these locations at these times at these intensities. But things could end up like this – or very different. But this is one of those images that helps make the threat seem as real as it is – just as long as you don’t focus on these as the only two possibilities (sorry to be so verbose, but I feel it important to emphasize the uncertainty):


On the left is the EURO model runs – Wednesday on top, Tuesday on bottom. The EURO has been more accurate in recent times than the GFS, which is on the right. The EURO has, from Tue to Wed, shifted its forecast from a weaker storm crossing the FL peninsula to a system that moves more southerly and strengthens in the Gulf and impacts LA/TX. The GFS in both cases predicts a weak low.

All of this is within the realm of possibility. Thus the message is: Monitor this system and prepare to have to make preparations. But don’t panic.

Lastly is the NHC’s outlook for 99L:


800 AM EDT WED AUG 24 2016

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical
Storm Gaston, located about 1000 miles west of the Cabo Verde

1. Satellite images, surface observations, and radar data indicate
that a broad area of low pressure associated with a tropical wave
is located over the northern Leeward Islands.  Showers and
thunderstorms have become more concentrated overnight and are
showing signs of organization, but the system still appears to lack
a well-defined circulation.  Although environmental conditions are
currently only marginally conducive for additional development, this
system could become a tropical depression at any time during the
next few days while it moves west-northwestward at about 15 mph
across the northern Leeward Islands, near or over Puerto Rico,
Hispaniola, and the Bahamas.  An Air Force Reserve Hurricane Hunter
aircraft is scheduled to investigate the disturbance late this
morning.  Gusty winds, heavy rains, and possible flash floods and
mudslides are expected to occur over portions of the Leeward
Islands, Puerto Rico, Hispaniola, and the southeastern and central
Bahamas.  Please consult products issued by your local
meteorological offices for further details. Interests in the
northwestern Bahamas and Florida should also monitor the progress of
this system.
* Formation chance through 48 hours...medium...60 percent
* Formation chance through 5 days...high...80 percent

Forecaster Brown