Tropical Storm Isaac, Part 2: Isaac Moving Into The Gulf Of Mexico-Hurricane Warnings For Morgan City, LA/MS/AL & FL Panhandle To Destin, FL

[dan88]

New vortex, gaining some lattitude, pressure down a bit. Drop had <5kt winds from 850mb (flight level) to surface

000

URNT12 KNHC 252323

VORTEX DATA MESSAGE AL092012

A. 25/23:09:40Z

B. 21 deg 44 min N

076 deg 31 min W

C. 850 mb 1403 m

D. 56 kt

E. 079 deg 43 nm

F. 141 deg 46 kt

G. 080 deg 41 nm

H. 997 mb

I. 15 C / 1523 m

J. 21 C / 1528 m

K. 16 C / NA

L. NA

M. NA

N. 1345 / 8

O. 0.02 / 1.5 nm

P. AF303 1609A ISAAC OB 16

MAX FL WIND 46 KT E QUAD 22:56:30Z

[Drz1111]

Bingo.

Sorry Phil, I kinda disagree. Horizontal mass transport at the bottom of the Ekman layer should still be along isopycnals. So if you have upwelling in a warm column down to only 200 m or so, and there is a need to pull in more water from the central Gulf to maintain mass continuity, you're still predominantly just advecting (relatively warm) 200 m water from the central-Gulf.

Also, I believe horizontal Ekman transport is usually only up to ~1 m/s even under strong winds, so it would probably only be relevant to a very slow moving storm. You're correct that it occurs during the development of La Nina, but that's over much longer time scales.

[Superstorm93]

Gaining latitude while pressures are dropping.

Lowest on the latest pass was 996

[NavarreDon]

Here is a crude picture of the gulf. In the Northern Gulf you can see a deepwater finger called the Desoto Caynon. This is a deep water area that comes fairly close to the coast

Here is a link to NOAA chart 411 for depth of the Gulf of Mexico. Thought these might be useful so there is a clear idea of what the storm will be working with as far a depth where ever it goes.

http://www.oceangraf.../zoom?chart=411

[Calderon]

Here is a crude picture of the gulf. In the Northern Gulf you can see a deepwater finger called the Desoto Caynon. This is a deep water area that comes fairly close to the coast

Here is a link to NOAA chart 411 for depth of the Gulf of Mexico. Thought these might be useful so there is a clear idea of what the storm will be working with as far a depth where ever it goes.

http://www.oceangraf.../zoom?chart=411

That's apparently one of the reasons why areas from Pensacola-Destin are more at risk for higher surges.

[masswinter]

Not sure if these have been mentioned on here or not? It is the GFDL ensemble forecast. The interesting thing about this ensemble is that the initial environmental conditions are not perturbed...instead the vortex structure and intensity, SST's or inner core moisture are slightly altered in each ensemble run. Specific details on how each ensemble member is perturbed are given on the webpage. The latest run is from 12z...but show that indeed the runs that used the weaker vortex and lower inner core moisture are the furthest west. In theory, these ensembles should give an idea on how the track could alter if the storm behaves different than expected in the short term. Eight of the runs are initialized with GFS fields and the other eight the GFS ensemble mean fields. This results in not much of a track difference in the 12z runs...but interestingly if one looks at the 6z runs...all the GFS ensemble initialized run were much further east than the OP GFS initialized runs.

http://data1.gfdl.noaa.gov/hurricane/gfdl_ensemble/

[tmagan]

00Z Observations

[Superstorm93]

Check out the SRSO IR loop.

We have some serious convection developing over the LLC. Recon isn't scheduled to make a fix until 1:30am

[winterymix]

http://data1.gfdl.no.../gfdl_ensemble/

That is a nice tool, thanks for posting it. It is a red flag,however, that the

track shifted west about 80 miles in a single run to run comparison.

I'd be trust a blend before accepting such a large disconnect. It also

totally disregards the EURO.

[wxsmwhrms]

Anybody have any new thoughts on the track? GFDL and HWRF all made serious shifts left, and there is now strong clustering of all the models no farther east than Destin other than the EC, and the EC ensemble implies a lot of members are quite a ways west. I am wondering if the fast forward speed (20 mph) is something that is being picked up on with later models and is enabling the system to get farther west before the weakness develops? Will be interesting to see if NHC shifts the track farther west tonight.

[DopplerWx]

How is the shear? If it has abated we could be looking at some nice intensification tonight with the convection popping over and around the LLC.

[wxsmwhrms]

That is a nice tool, thanks for posting it. It is a red flag,however, that the

track shifted west about 80 miles in a single run to run comparison.

I'd be trust a blend before accepting such a large disconnect. It also

totally disregards the EURO.

Did you look at that ensemble from the 18Z run? OMG! The farthest EAST member is Gulf Shores, and everything else is MS/AL except for the one that goes to HOU. That is a HUGE shift west from the 12Z version of this product.

Anyone have much experience with this?

[Superstorm93]

We could see steady intensification once the inner core begins to really get itself established in the convection.

Once this starts to release enough latent heat, shear should be a non-factor.

[masswinter]

That is a nice tool, thanks for posting it. It is a red flag,however, that the

track shifted west about 80 miles in a single run to run comparison.

I'd be trust a blend before accepting such a large disconnect. It also

totally disregards the EURO.

Yeah the 18z GFDL and its ensembles shifted way west. Since the initial environmental conditions are not perturbed...it makes some sense that there could be large run to run shifts. This ensemble is likely not a good tool to determine an envelope of track possibilities. However it could be useful for other things. For example, ensemble 2 is perturbed by increasing the vortex intensity and size...and this run is well right of the ensemble mean. Meanwhile...ensemble 3 is perturbed by decreasing the vortex intensity and size...and its track is well left of the ensemble mean. Since both of these runs use the same environmental initial conditions...I would think we could say that...all else being equal...the longer the storm stays weaker and less organized the further west it will go. This type of ensemble is probably best used in comparing differences in one individual member to another ....not necessarily using it like we use the GFS or ECMWF ensembles.

[Nikolai]

The new core is shaping up and it's looking fantastic! Cheers to diurnal maximums...

The 00z EURO is what's most interesting out of tonight's model suite, given it's the only model to really diverge from a NOLA-Mobile spread.

[wxsmwhrms]

Yeah the 18z GFDL and its ensembles shifted way west. Since the initial environmental conditions are not perturbed...it makes some sense that there could be large run to run shifts. This ensemble is likely not a good tool to determine an envelope of track possibilities. However it could be useful for other things. For example, ensemble 2 is perturbed by increasing the vortex intensity and size...and this run is well right of the ensemble mean. Meanwhile...ensemble 3 is perturbed by decreasing the vortex intensity and size...and its track is well left of the ensemble mean. Since both of these runs use the same environmental initial conditions...I would think we could say that...all else being equal...the longer the storm stays weaker and less organized the further west it will go. This type of ensemble is probably best used in comparing differences in one individual member to another ....not necessarily using it like we use the GFS or ECMWF ensembles.

Excellent info! Thanks!

[David Reimer]

0Z Early-cycle track guidance is quite clustered this evening with a dramatic west/northwest shift.

[Superstorm93]

Wow...

Large shift west with the 00z Dynamic.

With three whole days in the Gulf, this could be significantly stronger than forecast.

[Sunny and Warm]

0Z Early-cycle track guidance is quite clustered this evening with a dramatic west/northwest shift.

That is eye opening considering the 12z GFS, and I was never in the western camp. That said, I note that the BAM models are clustered as well, which would be a good sign that shear is still forecast to be a non-factor out in time. I would be interested in intensity based on that. Do you have that?

[DopplerWx]

Wow, amazing agreement in the 00z model suites, 3 days over prime conditions for intensification. Going to be a fun one to watch.

[Ginx snewx]

Read up on the Hurricane of 1812

[Superstorm93]

That is eye opening considering the 12z GFS, and I was never in the western camp. That said, I note that the BAM models are clustered as well, which would be a good sign that shear is still forecast to be a non-factor out in time. I would be interested in intensity based on that. Do you have that?

For single-digit shear numbers, much less than I would expect.

[huronicane]

That is eye opening considering the 12z GFS, and I was never in the western camp. That said, I note that the BAM models are clustered as well, which would be a good sign that shear is still forecast to be a non-factor out in time. I would be interested in intensity based on that. Do you have that?

http://www.ral.ucar.edu/hurricanes/realtime/plots/northatlantic/2012/al092012/intensity_early/aal09_2012082600_intensity_early.png

For all early cycle, etc. guidance plots:

http://www.ral.ucar.edu/guidance/realtime/plots/northatlantic/2012/al092012/

[Dsnowx53]

Anybody have any new thoughts on the track? GFDL and HWRF all made serious shifts left, and there is now strong clustering of all the models no farther east than Destin other than the EC, and the EC ensemble implies a lot of members are quite a ways west. I am wondering if the fast forward speed (20 mph) is something that is being picked up on with later models and is enabling the system to get farther west before the weakness develops? Will be interesting to see if NHC shifts the track farther west tonight.

I feel that people have been making definite landfall zones way too early. There is still a lot to be ironed out. I feel that unless the weakness and trough can turn Issac NE towards Panama City, then it's going to turn back to the NW towards the MS/AL border and maybe even towards MSY.

Ensembles have been showing east and west clusters for a reason, IMO, as I stated earlier with regards to the GFDL ensembles. A blend of the models might not be a good thing to do since it might be hard (though not impossible) for a middle track between the clusters to actually occur, given the synoptic pattern.

[Superstorm93]

I'm going to focus on the rapidly developing convective pattern we have here

Over 29C waters:

[Sunny and Warm]

For single-digit shear numbers, much less than I would expect.

It would be shocking at this point if it did not intensify to cat 3 at some point in the gulf with such benign conditions, but we all know that is never a given. Little shear and previously untraveled water with a consolidated center is ripe for rapid intensification. I also note that it is reconsolidating quite nicely this evening off Cuba. I could definitely see this as a cat 1 near Key West based on these parameters as well.

[tnweathernut]

I know this is way too soon to discuss a definititve track, but considering New Orleans...........................how are the levees and all the work they did? Did they just restore them to previous effectiveness OR enhance their capabilities? It would seem the clustered track as shown would have a HUGE impact. The angle would maximize any storm surge with the system and the possibiity of a strengthening CAT3 hitting could once again be devastating.

[WeatherX]

I'm going to focus on the rapidly developing convective pattern we have here

Over 29C waters:

Quick drive by hit, but that shot looks very attractive.

[wxsmwhrms]

I feel that people have been making definite landfall zones way too early. There is still a lot to be ironed out. I feel that unless the weakness and trough can turn Issac NE towards Panama City, then it's going to turn back to the NW towards the MS/AL border and maybe even towards MSY.

Ensembles have been showing east and west clusters for a reason, IMO, as I stated earlier with regards to the GFDL ensembles. A blend of the models might not be a good thing to do since it might be hard (though not impossible) for a middle track between the clusters to actually occur, given the synoptic pattern.

I don't disagree with this at all. I have been pretty much telling people the most likely zone is pretty much where NHC has it, the far western FL panhandle, but still a lot of uncertainty. However, as you say this is kind of a compromise between two highly plausible solutions, it keeps moving WNW into MS/AL/SE LA, or it turns into the weakness into the western/central FL panhandle and then NE. The in between scenario could happen if the models are a bit off on either of the features and the turn happens just right.

From a model perspective, it seems like the EC is the one that really has the eastern solution now, with the UK kind of the "in between" scenario and the GFS/Canadian and all the GFS-based models all in on the western solution. The thing that bugs me is up until the 12Z run today the EC had been in the more western camp, and it looks like a lot of its ensembles are still over there. If this fast movement continues, it would seem to me like the western camp becomes more plausible.

[winterymix]

...I would think we could say that...all else being equal...the longer the storm stays weaker and less organized the further west it will go. This type of ensemble is probably best used in comparing differences in one individual member to another ....not necessarily using it like we use the GFS or ECMWF ensembles.

Thank you, now we are rolling with good info.