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:
- Texas / Mexico
- New Orleans / Mississippi Gulf Coast
- 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):
ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION NINE DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 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. FORECAST POSITIONS AND MAX WINDS 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 NNNN