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Tropical Storm Isaac, Part 1: Moving Through The Eastern Caribbean Sea


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850mb center, 15.5N, 56.7W, 1003.5mb extrap

Little latitude gain since the passes made this afternoon... this is slightly less latitude than the intermediate advisory.

Edit: The wind center at 850 hPa might actually be displaced south of the surface center, which seems to have become less organized since earlier this afternoon despite the lower pressure.

eskk8g.png

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I've always been a proponent of the "teach a man to fish" philosophy..

The GEFS is almost always going to be of a lower strength because it is the mean of all of the GFS Ensembles. How ensembles work is taking the initial conditions and altering them slightly in different ways so that each ensemble will represent non-perfect starting positions because since there's no perfect observation network (especially over the ocean). The ensembles represent the, more or less "range" of potential scenarios/ outcomes. The main models (GFS,ECMWF,CMC etc.) only run one scenario, the "best guess" scenario, and run it at a much higher detail than the ensembles and thus the pressures will be lower and the picture "more complete/better" than the ensemble mean.

The fact that the low is 1001mb on the GEFS is pointing to the fact that there is fairly high certainty amongst the ensemble members that the cyclone will be near that point and in fact looking at each of the individual ensemble members of the 0z run. They are! Link to individual member loop

could this be a rare win for the GEM???? Just a thought

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Lots of heavy convection, with 9 straight observations spaced 30 seconds apart of at least 39mm/hr convection going West along 15.25N

060000 1518N 05629W 8432 01529 //// +151 //// 152006 016 059 040 01

060030 1516N 05630W 8435 01534 //// +151 //// 201007 010 059 043 01

060100 1515N 05631W 8433 01534 //// +150 //// 189015 018 056 042 05

060130 1515N 05632W 8428 01540 //// +149 //// 169008 013 057 045 01

060200 1515N 05634W 8424 01544 //// +148 //// 181013 016 056 044 01

060230 1515N 05636W 8424 01543 //// +151 //// 211013 017 052 053 01

060300 1515N 05637W 8431 01532 //// +154 //// 233011 016 053 053 01

060330 1515N 05639W 8430 01535 //// +154 //// 277010 012 042 044 01

060400 1515N 05641W 8435 01527 //// +155 //// 288017 019 038 039 01

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the Euro hold's true to form, runs it right up the Yucatan slot into the GOM....Love the consistency of this model....on the other hand the GEM is consistent as well....the GFS is all over the board at this time, I think it will be either a Gem or Euro solution at this time, they are the two most consistent models, right now I lean towards the Euro

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the Euro hold's true to form, runs it right up the Yucatan slot into the GOM....Love the consistency of this model....on the other hand the GEM is consistent as well....the GFS is all over the board at this time, I think it will be either a Gem or Euro solution at this time, they are the two most consistent models, right now I lean towards the Euro

Lol, all the models have been consistent on their respective tracks. I don't take back my Euro has been crap this year statement. The Euro will bend soon, I think.

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Eh, the Euro will eventually fall into the GFS camp over the next couple of runs. Euro has been crap this year, lol.

With the 12z Euro solution plus it's ensemble mean, coupled with what the 0z Op Euro is showing, I have a hard time believing the other models at this point...of course I could be wrong with that.

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With the 12z Euro solution plus it's ensemble mean, coupled with what the 0z Op Euro is showing, I have a hard time believing the other models at this point...of course I could be wrong with that.

Wasn't the ensemble mean east of the OP? Correct me if I'm wrong.

Just observing from recent years though, Hispaniola tends to "suck" TCs in (see Ernesto 06, Gustav 08). This has already happened with a typhoon in Taiwan a few weeks back. I think the track around Hispaniola will be highly nonlinear and difficult to predict in advance.

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The ECMWF is much faster this run, with the system all the way in the middle of the Gulf of Mexico at 168 hours. That is consistent with a stronger ridge. I honestly have no idea if its right though, its so different from the rest of the guidance.

One argument is that Hispaniola causes such a detrimental effect on the system, after becoming vertically coupled it decouples again. The ECMWF is supporting this solution, which allows for a further west track. On the flip side, the GFS/GGEM support the storm remaining vertically coupled through the passage of Hispaniola so its able to take advantage of the brief weakness and track further NW. This is one of those forecasts where its probably just as good to flip a coin at this point.

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Wasn't the ensemble mean east of the OP? Correct me if I'm wrong.

Just observing from recent years though, Hispaniola tends to "suck" TCs in (see Ernesto 06, Gustav 08). This has already happened with a typhoon in Taiwan a few weeks back. I think the track around Hispaniola will be highly nonlinear and difficult to predict in advance.

Yes, although the ECMWF continues to advertise a much stronger ridge than the GFS. Nobody has folded their cards yet.

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Wasn't the ensemble mean east of the OP? Correct me if I'm wrong.

Just observing from recent years though, Hispaniola tends to "suck" TCs in (see Ernesto 06, Gustav 08). This has already happened with a typhoon in Taiwan a few weeks back. I think the track around Hispaniola will be highly nonlinear and difficult to predict in advance.

Here is what this mornings 12z Euro ensemble showed

12zecmwfenstropical500mbSLP216.gif

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The ECMWF is much faster this run, with the system all the way in the middle of the Gulf of Mexico at 168 hours. That is consistent with a stronger ridge. I honestly have no idea if its right though, its so different from the rest of the guidance.

One argument is that Hispaniola causes such a detrimental effect on the system, after becoming vertically coupled it decouples again. The ECMWF is supporting this solution, which allows for a further west track. On the flip side, the GFS/GGEM support the storm remaining vertically coupled through the passage of Hispaniola so its able to take advantage of the brief weakness and track further NW. This is one of those forecasts where its probably just as good to flip a coin at this point.

Interesting. Its not that the euro is showing a much different setup than the other models that brings Isaac west, but a type of interaction with Hispaniola that changes the path. Right now its the only model in the world that's showing that though

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The Euro is so far away from all other models I have a hard time believing it, not impossible but for now I am in NHC's camp. the key is the strength. if it can stay a weak TS for the next 3 days, the Euro has a shot. Otherwise, hello Hispaniola and Cuba, then a strong TS or cat 1 hurricane hitting somewhere in FL.

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The Euro is so far away from all other models I have a hard time believing it, not impossible but for now I am in NHC's camp. the key is the strength. if it can stay a weak TS for the next 3 days, the Euro has a shot. Otherwise, hello Hispaniola and Cuba, then a strong TS or cat 1 hurricane hitting somewhere in FL.

Its not the intensity over the next few days that seems to be the issue... in fact Isaac is stronger in this ECWMF run pre-Hispaniola than the 12z run. Its what the island does to the circulation that is key. Does it disrupt it to the point it no longer is vertically stacked. Thats the key question. The ECMWF says yes, the GFS says no.

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Here are my thoughts: Going back to the basic's as rude as they are:

#1 do you have a good run to run consensus between the different solutions ? In this case no. The GFS and the GEM from run to run are horrible, they are all over the board.

#2 can you find a deterministic model that shows run to run consistently? In this case yes, it only belongs to the Euro, the OP has been very consistent the last 3 runs.

#3 does the most consistent model show support from its ensemble members? In this case the Euro shows strong support.

There fore I think there is a 70% chance of seeing of major storm somewhere in the GOM

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Here are my thoughts: Going back to the basic's as rude as they are:

#1 do you have a good run to run consensus between the different solutions ? In this case no. The GFS and the GEM from run to run are horrible, they are all over the board.

#2 can you find a deterministic model that shows run to run consistently? In this case yes, it only belongs to the Euro, the OP has been very consistent the last 3 runs.

#3 does the most consistent model show support from its ensemble members? In this case the Euro shows strong support.

There fore I think there is a 70% chance of seeing of major storm somewhere in the GOM

Not going to give it that yet, but I will say this consistency from the Euro with the way it interacts with Hispaniola is intriguing.

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000

URNT12 KNHC 220730

VORTEX DATA MESSAGE AL092012

A. 22/06:00:30Z

B. 15 deg 16 min N

056 deg 29 min W

C. 850 mb 1470 m

D. 29 kt

E. 006 deg 20 nm

F. 122 deg 34 kt

G. 353 deg 19 nm

H. 1006 mb

I. 20 C / 1523 m

J. 17 C / 1527 m

K. 18 C / NA

L. NA

M. C8

N. 12345 / 8

O. 0.02 / 1 nm

P. AF307 0209A ISAAC OB 05

MAX FL WIND 47 KT NE QUAD 06:26:00Z

MAX FL TEMP 21 C 357 / 20 NM FROM FL CNTR

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Its not the intensity over the next few days that seems to be the issue... in fact Isaac is stronger in this ECWMF run pre-Hispaniola than the 12z run. Its what the island does to the circulation that is key. Does it disrupt it to the point it no longer is vertically stacked. Thats the key question. The ECMWF says yes, the GFS says no.

Phil,

Does my hypothesis about the ECMWF making the lee cyclone dominant and the GFS keeping the original vortex dominant, have any credence? Could the difference in the physics of the models be the difference here, or are the differences more synoptic-scale in nature?

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That fix looks odd. There were several pressures lower to the north, we may get another relocation on this next pass. This thing is very disorganized, which might lend a bit more weight to the Euro. BTW, the ensembles are trickling in, very weak and far south at 132. This is a toughie all right. One thing to remember, the Euro was an outlier this year with Debby, and it was dead wrong.

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Yes, although the ECMWF continues to advertise a much stronger ridge than the GFS. Nobody has folded their cards yet.

I love your analogy. :)

Feeling pretty safe here on Cape Fear but looking through my binoculars every now and then just to make sure nothing sneaks up on me. By the way, where the heck are all the Florida weather geeks? That's one silent group ain't it?

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Seems to be closer to where recon has been finding flight level center this time, which has been just south of 15.5N all night.

000

URNT12 KNHC 220834

VORTEX DATA MESSAGE AL092012

A. 22/08:09:40Z

B. 15 deg 29 min N

057 deg 20 min W

C. 850 mb 1454 m

D. 43 kt

E. 300 deg 20 nm

F. 057 deg 17 kt

G. 297 deg 25 nm

H. 1004 mb

I. 18 C / 1527 m

J. 19 C / 1521 m

K. 19 C / NA

L. NA

M. C10

N. 12345 / 8

O. 0.02 / 1 nm

P. AF307 0209A ISAAC OB 10

MAX FL WIND 47 KT NE QUAD 06:26:00Z

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