The National Hurricane Center is now issuing advisories on newly-formed Tropical Depression Nine, which is forecast to become a Tropical Storm probably some time on Monday.

There remains a huge amount of uncertainty for the track and strength. Basically, two higher-confidence models are disagreeing with a number of lower-confidence models; and the two higher confidence models disagree with each other. We’ll see what happens tomorrow as the system moves into the Gulf of Mexico. Meanwhile, lots of graphics now as the NHC has issued the first 4pm update. I’ll start with the official NHC cone:


Please remember that the cone doesn’t show the predicted extent of the storm; rather, it shows where the *center* of the system may go. Thus, the current NHC cone shows currently predicted landfall to be anywhere from Pensacola to Cape Coral / Ft. Myers. You may well note that this cone of uncertainty is on the larger side; that’s with good reason.

Here’s the current spag:


Based on this and previous spag, it looks like there’s three forecast clusters, from west to east as follows:

  1. Texas / Mexico
  2. New Orleans / Mississippi Gulf Coast
  3. Florida Panhandle / Big Bend / Tampa / Cape Coral, with a focus on the Big Bend

NHC is going with the Big Bend solution, but as mentioned above, basically all of Florida’s gulf and west coast is in the cone.

NHC is primarily following the GFS model. Here’s the GFS ensemble (a single model run multiple times with different starting conditions to account for the possibility of measurement on the ground / in the air being slightly different):


Note that the GFS ensemble, which has previously been itself very spaghettified, is now relatively in agreement; that is, even given some different starting conditions, the GFS has internal certainty about its forecast. This is one of the models I mentioned earlier – it’s a higher confidence model in general. I don’t have current easy access to the EURO ensemble to compare, but the main EURO forecast is part of the spag posted earlier.

In the next couple of days, we should see which of these three general forecast tracks actually happens; or perhaps things will shift again. Basically, remember that most of the time, because of the sheer complexity of the atmosphere and all the conditions, we just can’t make strong predictions until systems get closer to land. But things are always getting better as time goes on.

So for this forecast, here’s the current tropical force wind forecast:


Sooo… it’s wide open, really. Very low confidence all around.

Let’s talk strength: Most models have TD9 as a Tropical Storm. Outliers show Cat1 or TD, and one silly model is saying, “OMG! OMG! CAT5!!!”


Expect a Tropical Storm. Might be a Cat1 – be prepared for that – and we might get lucky and it’ll just be a Tropical Depression.

Finally, here’s the NHC Forecast Discussion. I always find these plus the graphics to allow me to give better predictions that many local-news folks (especially if you account for me saying “It’s very uncertain!” as I am now, when MANY idiots out there – professional and amateur – try to claim they can predict the landfall this far out with this much uncertainty, which I think is foolish):


500 PM EDT SUN AUG 28 2016

Data from a NOAA Hurricane Hunter aircraft indicate that the area of
low pressure located in the Florida Straits now has a well-defined
center.  Satellite imagery shows a significant increase in the
convective organization today, and as a result the system is now
classified as a tropical cyclone.  The initial intensity is set to
30 kt based on the highest believable wind data from the aircraft,
which reported a central pressure of 1009 mb.

The depression will be moving through a marginal environment for
intensification during the next day or so, with vertical shear of
15 to 20 kt.  As a result only slow strengthening is expected in
the short term.  Later on, the environment may improve a little as
the shear is forecast to decrease somewhat and become
southwesterly, which should allow for a little more strengthening.
However, there are mixed signals in the model guidance, with the
ECMWF now showing the cyclone dissipating in the Gulf, while the
GFS delays development until 4-5 days.  Much of the tropical
cyclone guidance is more aggressive.  Given this uncertainty, the
NHC intensity forecast is quite conservative and shows the system
peaking at 45 kt, below all the explicit intensity guidance in
consideration of the negative signal from the ECMWF.  Needless to
say, the confidence in the intensity forecast is even lower than
usual for this system.

The initial motion estimate is an uncertain 270/09 given the recent
formation of the center.  The cyclone will be steered in the short
range by a mid-level ridge centered over the southeastern United
States.  This ridge will weaken in 2-3 days, which will cause the
cyclone to slow down and turn northward during this time.  Late in
the period a northeastward acceleration is expected ahead of an
approaching mid-latitude trough.  There is reasonable agreement in
the track of the cyclone in the global model guidance, although
there is a fair bit of along-track spread late in the period.  The
NHC forecast is close to a consensus of the GFS and ECMWF through
day 4 and is a little faster than the GFS and GEFS ensemble mean at
day 5.


INIT  28/2100Z 23.7N  81.7W   30 KT  35 MPH
 12H  29/0600Z 23.9N  83.6W   30 KT  35 MPH
 24H  29/1800Z 24.3N  85.4W   35 KT  40 MPH
 36H  30/0600Z 24.6N  86.8W   35 KT  40 MPH
 48H  30/1800Z 25.1N  87.6W   40 KT  45 MPH
 72H  31/1800Z 26.8N  87.4W   45 KT  50 MPH
 96H  01/1800Z 29.0N  84.5W   45 KT  50 MPH
120H  02/1800Z 31.0N  80.0W   45 KT  50 MPH

Forecaster Brennan