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

[turtlehurricane]

I made a schematic of the possible effect the Cuban coastline could have on Isaac's motion. Rising is favored west of the center where air converges at the coast, thus generating lower pressure, and sinking is favored east of the center where air diverges at the coast, generating higher pressure. This results in the low propagating westward along the coast since it travels in the direction of falling pressure. This sort of effect can dominate in weak systems and keep them stuck to the coast, Ernesto 2006 is a good example.

[ALhurricane]

I like the steady state idea. GFS slows it down tremendously and adds a NNW component. Shear should be low near FL/AL landfall and this should balance the lack of latent heat in the north GOM esp. with upwelling. At landfall, the winds will be a lesser factor than 9+ inch rains and spin up tornadoes. My stoopid SIL lives in Spanish Fort, AL hee hee.

That track is a bad scenario for Mobile Bay surge. It would be significant. I am in Daphne and really don't care to see this thing come that far west. Need to see how it survives in the next 24 hours first.

[tmagan]

16Z Observations

[PSUBlizzicane2007]

I really, really, really doubt that will occur, given the average to below-average OHC in the region plus the potential for upwelling due to such slow movement. Plus, I am no longer so sure that Isaac will retain enough structure to re-intensify by the time it leaves Cuba...particularly with the LLC becoming detatched from the MLC and remaining over land.

This post makes no sense. The OHC is fine in the Gulf, shear and dry air will be a nonfactor there, and models generally are not worried about what is happening right now with respect to Isaac.

[WhiteoutWX]

Currently Issac is having to fight off frictional effects of the higher terrain in eastern Cuba as well as the low pressure in close proximity to its west. It will be interesting to see what we have left when it finally clears the Cuban coast later today/tonight.

[Superstorm93]

I really wasn't expecting to come in and see such major problems with Isaac this afternoon.

I'll be very surprised if this is a hurricane by the time it reaches the keys due to the significant land interaction that has taken place.

[Ginx snewx]

well lets see what happens now, off the coast and ready to rock?

[icebreaker5221]

Word of caution: OHC is a good indicator of potential for upwelling over deep waters (inversely proportional of course) but has to be interpreted differently near the shore. This is especially true in the NE GOM where ocean depth is only ~100 m or so within 200 km of the west coast of FL. OHC is a calculation of vertically integrated heat. So no matter how warm the shallows are, you're still going to get low OHC just because you're integrating over a relatively small depth. Most storms weaken in the N Gulf because of increased shear and dry air coming in off the plains, not because of upwelling.

Second, although the GFS and ECMWF are both strengthening Isaac very rapidly in the Gulf, they may be overly ambitious in terms of recovery time for the core. I believe this to be somewhat of a model resolution issue. Unless you have 1 km resolution or less, turbulent structures in the core of the storm that act to dissipate kinetic energy will be "smoothed out" in the model, allowing the vortex to regain symmetry much more quickly than it should. It doesn't me we won't see RI, just a word of caution.

[wxsmwhrms]

Two points:

First off, is it a big surprise that Isaac is weaker this afternoon and probably not going to make hurricane before S FL. I mean, I was one of the ones that was trying to minimize people writing off Isaac because of going over Hispaniola, but even I was thinking more about that it wouldn't be so decimated that it couldn't intensify over the Gulf. I don't think any of the models have shown any significant increase in intensity until it gets close to the Keys.

Secondly, I have seen the GFS try to show this major slowing as a storm approaches the northern Gulf Coast more times than I can count. That kind of track rarely occurs, Georges being a notable exception. Not saying it can't or won't happen, I just wouldn't be banking on it as far as upwelling, etc.

[wxsmwhrms]

12Z GFS ensemble has made a large shift left. Farthest east member for landfall (based on 1000 mb contour) looks to be about Panama City, with SW member threatening Houston/Galveston.

[WhiteoutWX]

12Z GFS ensemble has made a large shift left. Farthest east member for landfall (based on 1000 mb contour) looks to be about Panama City, with SW member threatening Houston/Galveston.

Link? The farthest left member I can find on the e-wall page is around New Orleans.

[BeauDodson]

New EC struggles with intensity. Was hoping for it to maintain some west trend - looks east. We desperately need rain in this region. 12z appears to be the Florida Panhandle.

[MN Transplant]

Guess I'll post it

[Nikolai]

12z EURO is dramatically different from 00z by hour 21... pressure around 990MB and center offshore Cuba while the 00z had it barely sub-1000 and still straddling the coast.

[deltadog03]

EURO goes EAST landfall near PCB....Weakness is DEF. stronger this run...AND this is a potent CANE

[MN Transplant]

Looks like Apalachicola for the Euro.

[Brewers]

Link? The farthest left member I can find on the e-wall page is around New Orleans.

[wxsmwhrms]

Too funny, GFS goes left, ECMWF goes right and it now the right most model over AQQ. WTF?! :-)

Consistency, baby!

[WhiteoutWX]

Thanks I wasn't looking at the storm specific ensemble tracks.

I don't know what to make of the Euro shifting right. GFS and Euro have now flipped their respective solutions with the GFS west and Euro east. I suspect they are windshield wiping right now and will settle somewhere in the middle.

The fact that a signifcant number of GFS ensemble members are west gives some pause,however. If the majority of Euro ensembles stay west of the OP would lead me to believe the 12z OP Euro was just a blip.

[Ground Scouring]

Isaac is looking better on recent satellite frames...the recent increase near the center may indicate dry air is mixing out. Also, the shape of the cluster is similar to situations in which I have seen systems steadily intensify...if convection continues to increase, the center may actually reform NE, off NE Cuba, and then quickly haul WNW as shown on the ECMWF in 24 hours. Currently, the central vorticity is being stretched over Cuba, potentially leading to differential vorticity advection co-locating with the convergence offshore.

[Shawn]

Rest of the Run: http://meteocentre.com/models/explorateur.php?lang=en&map=na&run=12&mod=gemglb&stn=PNMPR&hh=000&comp=1&runb=12&mod2=gemglb&stn2=PNMPR&hh2=144&fixhh=1

[Dunkman]

Here's the wundermap version of the Euro landfall at 84.

[wxsmwhrms]

So just to summarize the landfall points:

Today's 12Z runs:

Canadian - MSY

GEFS mean - MS coast

GFS - MS/AL border

GFDL and UK - Destin

ECMWF - PCB-AQQ

Yesterday's 12Z runs:

Canadian - E of FL

GEFS mean and GFS - Near AQQ

UKMET - Destin-PCB

ECMWF - MS/AL border

One thing I will say is that while the ops ECMWF has been waffling around between runs to LCH and PCB for the last few days, the ensemble mean has been more consistent, gradually shifting from SE LA to more like the MS/AL line over the last several runs. Want to see what it shows.

Also, here's the other question, is this a case where it ends up in the middle (which is probably the best you can do for a forecast right now), or is this a case where there is a very subtle difference in the trough/ridge interaction and it will be either one or the other (NE turn toward PCB/AQQ or more NW motion continuing toward MS/AL)? The last time we had a situation with Debby where either the ridge was going to guide it west to TX or the trough take it NE toward FL, the trough won. But it was the GFS that showed that correctly, not the Euro, LOL.

[OUGrad05]

Thanks I wasn't looking at the storm specific ensemble tracks.

I don't know what to make of the Euro shifting right. GFS and Euro have now flipped their respective solutions with the GFS west and Euro east. I suspect they are windshield wiping right now and will settle somewhere in the middle.

The fact that a signifcant number of GFS ensemble members are west gives some pause,however. If the majority of Euro ensembles stay west of the OP would lead me to believe the 12z OP Euro was just a blip.

I agree, we need to see if the Euro position to the east is just an anomaly. But I have a feeling this is going to bounce around a bit in the coming hours. Until it reorganizes some over water it will be a volatile situation for predicting landfall.

I'm hoping we have something more solid by this time tomorrow. I've got some friends at basically target zero, Pensacola FL.

[Srain]

MODEL DIAGNOSTIC DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD

239 PM EDT SAT AUG 25 2012

VALID AUG 25/1200 UTC THRU AUG 29/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR

INGEST...

FINAL 12Z MODEL EVALUATION INCLUDING THE ECMWF

INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY IMPACT THE

LARGE SCALE FORECAST.

...TROPICAL STORM ISAAC...

MODEL GUIDANCE CONTINUES TO INDICATE A TRACK TOWARD THE GULF COAST

OF THE U.S. IN ABOUT 4 DAYS. MID LATITUDE TROUGHING WILL WEAKEN

FROM THE NORTHEAST GULF UP THE EAST COAST OF THE U.S...WHICH

LEAVES ROOM FOR THE TROPICAL CYCLONE TO BE DRAWN UP TOWARD AND

EVENTUALLY INTERACT WITH A BAROCLINIC TROUGH THAT DIGS INTO THE

OHIO VALLEY TO LOWER MISSISSIPPI VALLEY BY THAT TIME. THERE IS

STILL CONSIDERABLE UNCERTAINTY ON THE SUB-SYNOPTIC

SCALE...HOWEVER...AND MODEL RUN TO RUN DIFFERENCES WITH RESPECT TO

THE EXACT TRACK WILL CONTINUE.

THE 12Z UKMET AND ECMWF ARE VERY CLOSE TO THE OFFICIAL TRACK. ONE

OF THE MORE VARIABLE MODELS HAS BEEN THE NAM...BUT OVER THE PAST

FOUR CYCLES IT HAS MOVED ITS TRACK FROM A POSITION WELL LEFT OF

THE OFFICIAL NATIONAL HURRICANE CENTER TRACK...TOWARD SOMETHING

THAT IS BETTER ALIGNED WITH THE OFFICIAL TRACK. THE 12Z NAM

DOES...HOWEVER...BEGIN ITS RUN WITH A NORTHWARD JOG THAT SPREADS

HEAVY RAIN A LITTLE FARTHER NORTHWARD IN FLORIDA ON SUNDAY

COMPARED TO CONSENSUS. THE 12Z GFS REMAINED CONSISTENT WITH ITSELF

AND THE OFFICIAL TRACK THROUGH MONDAY MORNING...BUT IT THEN LEANS

FARTHER WEST INTO THE GULF AFTER 27/12Z...WHICH IS AN IDEA THAT

HAD SUPPORT FROM MANY OF THE 00Z ECMWF ENSEMBLE MEMBERS. THE 12Z

CANADIAN IS EVEN FARTHER WEST. PLEASE REFER TO THE NATIONAL

HURRICANE CENTER FOR OFFICIAL TRACK AND STRENGTH FORECASTS...AND

ADDITIONAL INFORMATION.

[tmagan]

18Z Observations

[OUGrad05]

18Z Observations

That puts the center location well to the west of the official point.

[wxsmwhrms]

This to me is interesting from the PMD:

THE 12Z GFS REMAINED CONSISTENT WITH ITSELF

AND THE OFFICIAL TRACK THROUGH MONDAY MORNING...BUT IT THEN LEANS

FARTHER WEST INTO THE GULF AFTER 27/12Z...WHICH IS AN IDEA THAT

HAD SUPPORT FROM MANY OF THE 00Z ECMWF ENSEMBLE MEMBERS.

If anyone out there has access to the EC ensembles would be willing to post of discussion of what they show today, that would awesome.

[tmagan]

That puts the center location well to the west of the official point.

Don't get too caught up in that. Limited observations, didn't have time to quality control them.

[turtlehurricane]

Recon finding 50 mph southerly winds east of the center, should get a fix soon if it's over water, but that's not a sure thing.

Also checkout the new GFDL ensemble products, this will be a great tool http://data1.gfdl.noaa.gov/hurricane/gfdl_ensemble/?STORMID=09L&YMDH=2012082512_ISAAC09L∏=