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


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I still think the Euro is hampered by having the storm too weak. If the flow is currently slightly WSW for a deeper storm, will that still be the cast past 60 W? Or would a deeper storm move more NW than a shallow one as the ridge weakens in the central Caribbean? Looking at the Euro compared to the CMC, BAM deep, HWRF, etc.the strength of the storm is what stands out to me on all of the models that show a Bahamas threat.

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I still think the Euro is hampered by having the storm too weak. If the flow is currently slightly WSW for a deeper storm, will that still be the cast past 60 W? Or would a deeper storm move more NW than a shallow one as the ridge weakens in the central Caribbean? Looking at the Euro compared to the CMC, BAM deep, HWRF, etc.the strength of the storm is what stands out to me on all of the models that show a Bahamas threat.

In the short term a more vertically deep storm results in a further south track due To the orientation of the mid-level ridge. As the ridge slowly erodes, that path of motion will switch from WSW to W to WNW. The question in the long term is how much this ridge breaks down and does it allow TD9 to move over Hispaniola and Cuba. Questions I'm not 100% sure of at this time, although I'm leaning towards the ECMWF. It should be noted the GFS and GGEM are both weaker than the ECMWF when they make their initial NW turn, so in the medium to long range, so strength of the storm doesn't seem to play a major role in whether or not TD9 is influenced by the weakness.

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At 06Z there now isn't a single GFS ensemble member that actually enters the GOM at any point, which is pretty interesting.

HPC:

PRELIMINARY UPDATE...

USED THE 00Z/21 ECENS MEAN TO UPDATE THE PRELIMINARY FRONTS AND

PRESSURES FOR DAYS 3 THROUGH 7. THE ECENS MEAN SHARED MORE IN

COMMON WITH THE VARIOUS GLOBAL DETERMINISTIC MODELS THAN THE GEFS

MEAN...THE SAID DETERMINISTIC GUIDANCE SHOWING ENOUGH SPREAD

THROUGH THE PERIOD TO NOT TRUST THEIR DETAILS. EXTRAPOLATED THE

09Z/21 NATIONAL HURRICANE CENTER FORECAST FOR THE DEPICTION OF

TROPICAL DEPRESSION NINE...WHICH WOULD TAKE THE SYSTEM TOWARD THE

FLORIDA PENINSULA DAYS 6 AND 7. WILL REFINE THE TRACK OF THIS

POTENTIAL HURRICANE DURING THE MIDDAY COORDINATION CALL.

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In the short term a more vertically deep storm results in a further south track due To the orientation of the mid-level ridge. As the ridge slowly erodes that path of motion will switch from WSW to W to WNW. The question in the long term is how much this ridge breaks down and does it allow TD9 to move over Hispaniola and Cuba. Questions I'm not 100% side at this time, although I'm leanin towards the ECMWF. It should be noted the GFS and GGEM are both weaker than the ECMWF when they make their initial NW turn, so in the medium to long range, so strength of the storm doesn't seem to play a major role in whether or not TD9 is influenced by the weakness.

Any thoughts on why the BAM deep is a right outlier compared to shallow or medium?

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Nothing like a questionable center location in the morning to get the mind thinking.

Recon should be in by early afternoon to give us a fix on whats actually happening under that convection.

2. SUSPECT AREA (APPROACHING LESSER ANTILLES)

FLIGHT ONE --TEAL 71--

A. 21/1800Z

B. AFXXX 01DDA INVEST

C. 21/1530Z

D. 16.2N 54.5W

E. 21/1730Z TO 21/2200Z

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This is significantly better organized than Ernesto and Helene were at this stage IMO. The better organization, the favorable environmental conditions currently and into the eastern Caribbean, and the stronger global model intensities suggest a much different outcome than those two, at least in the central/eastern Caribbean. I'm not buying the "it's moving too fast" and the "vortex is tilted/centers are misaligned" scenario as much this time.

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Only focusing on structure...

09L does appear to have a very well defined low level circulation (for the time being) with some very moist air in the southern inflow. Also note how large the circulation is as a whole.

In the Atlantic, size does matter. Especially when one is forecast to take on Hispaniola at some point.

20120821.1311.metopa.x.color_89_150.09LNINE.30kts-1007mb-151N-520W.100pc.jpg

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This is significantly better organized than Ernesto and Helene were at this stage IMO. The better organization, the favorable environmental conditions currently and into the eastern Caribbean, and the stronger global model intensities suggest a much different outcome than those two, at least in the central/eastern Caribbean. I'm not buying the "it's moving too fast" and the "vortex is tilted/centers are misaligned" scenario as much this time.

I agree. In addition, the shear vector is in a direction that won't be injecting the system with continued bouts of dry air, since the TPW to the east of TD#9 is actually quite high.

1t5szr.gif

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The over or N of Guadeloupe seems unrealistic (this is shown by the models, even the current 12z GFS)...that would mean gaining over 1 degree in latitude...it should be moving 280-285 by now, which it isn´t. This may seem as nitpicking, but this could mean a farther south track off Hispaniola (or La Española *winks* PSUBlizzicane). There´s even some NEerly shear, which might hint at a stronger than progged mid/upper level ridge.

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