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

[LakeEffectKing]

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.

This times one thousand.

[winterymix]

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?

No experience, but otherwise, I was remarking on the same idea that you have.

It seems that from the standpoint of classic statistics, one would want to

see a couple more model cycles before upping one's confidence.

If I were giving guidance to the general public, it would be socially responsible

to explain the reasons for the cone of uncertainty at landfall. Once we are 48

hours out from landfall on the southern GOM, I'd hope that the site-of-landfall confidence is

tighter for those making preparations.

NHC does a good job explaining the cone of uncertaintly but I think it has to be

put into terms that a person with an eighth grade education can grasp. Too many

people think that the zone of uncertainty is a cop out implying that Mets are clueless.

[Dsnowx53]

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.

Right, well stated. Though even perhaps the far W Panhandle is still the in-between zone. The in-between scenario would kind of be "threading the needle", so to speak, between the weakness, trough, and ridge, which I feel is unlikely. The west/central FL Panhandle is track "A", IMO, and MS/AL border/MSY is track "B". The in-between zone is not a huge one, but certainly big enough to where I think it is worth mentioning as an area of unlikely landfall relative to the areas west and east of it.

I'm honestly leaning towards the west camp. I am by no means an expert, but I'm very much in the belief that taking a step back and looking at the pattern in a broad, synoptic sense, the ridging is a large scale feature that we kinda know will exist and be a strong potential factor. The troughing and ULL, while not insignificant features, are a small enough scale so that there is less room for error in Issac's track that would actually result in a very direct impact from them.

The fact that ALL the models, even when shifting east, had shown Issac stalling for days is a strong indicator that the ridging will definitely become dominant at some point. The trough catching Issac in time, however, is much less certain. So as you said, a bit of a faster forward speed is all that needs to happen for the trough to miss this thing.

[jhamps10]

First thoughts on seeing the spaghetti plots, I hope the Army Corps have the flood walls in New Orleans fixed, Correct me if I am wrong mets, but would a ESE/WNW track like that get New Orleans in the prime storm surge spot, with it coming in from the Lake, and the GOM? This is quite the shift, and one would expect the NHC to be forced to move the track west at 11PM because it looks like maybe 1 or 2 models on the spaghetti charts come anywhere near the NHC's current forecast...

[KBPPradmet11]

Did recon really just find windspeeds at 108 mph?

I might be going out on a limb here, but I'll say probably not.

[Sunny and Warm]

Some great insight in the last hour. It appears final track may be dependent on both intensity as well as speed of Isaac. Faster and weaker may provide a left solution. Slower and stronger a more right solution, with something in between for less of each. Isaac is moving more quickly than anticipated than at this time yesterday, so a faster solution is on the table in the near term where the ridge should influence a greater left turn. On the other hand, Isaac is getting its act together this evening more robustly than I anticipated, so that tendency is more right possibly. All that said, I agree with others that it is not apparent yet that left or right is correct, and that a middle ground does exist where one parameter cancels out the other. However, I tend to believe that a faster pace for Isaac will lead to a left solution, as it may overpower any effects intensity may have.

[turtlehurricane]

The 60 mph winds that NHC is using to define Isaac's intensity are over 100 miles from the center, winds anywhere near the center on the recent pass are 30-50 mph. This has been the case all day, the strongest winds are in the easterlies north of the storm since that's the part that's been over water, and the wind pattern has been sporadic bursts more than truly organized. I think it's a bit dishonest to keep Isaac as a strong tropical storm all day as if it hasn't weakened... especially given the lack of convection and tenuous sfc circulation most of the day.

It is finally gaining convection near the center but its got a long way to go before it can ever reasonably called a hurricane. I don't disagree with the NHC forecast that much since it makes sense that it could become a cane by the time it enters the Gulf, but I don't see the reason for hurricane advisories in South Florida besides a watch in the lower and middle keys. It's not like hurricane force winds are going to be over a broad area immediately when it crosses the hurricane threshold, only a small region will see that.

[CUmet]

Echoing what other good mets have said here, but the upper air setup as depicted by various reliable global models from here on out is very favorable for a lot of intensification. Given how little interaction this will have with Cuba and the remaining amount of time over water, a major hurricane landfall is becoming a very real possibility. I expect Isaac to take its time organizing its inner core over the next 24 hours, and I don't expect RI to occur until at least it clears the Florida Keys.

[Superstorm93]

Recon will be taking off in 20 minutes

Won't have our first center fix until 1:30am or so.

Center has probably become at least marginally better defined. It is also plausible that Isaac may have even been able to lower it's pressures a bit since the USAF plane left.

Pressures fell from 999 or so (when this left Cuba), to 996 when they were leaving.

[dan88]

The 60 mph winds that NHC is using to define Isaac's intensity are over 100 miles from the center, winds anywhere near the center on the recent pass are 30-50 mph. This has been the case all day, the strongest winds are in the easterlies north of the storm since that's the part that's been over water, and the wind pattern has been sporadic bursts more than truly organized. I think it's dishonest to keep Isaac as a strong tropical storm all day as if it hasn't weakened... especially given the lack of convection and tenuous sfc circulation most of the day.

The recon plan did have a dropsonde with 47kt at the surface at 4:21 this afternoon, shortly before the 5pm advisory, which had a splash point roughly 40nm from where recon fixed the center at 5:14 this afternoon, or about 25nm from the 5pm advisory location, which at least at that point in time seems to justify the 5pm intensity of 50kt.

[LakeEffectKing]

Echoing what other good mets have said here, but the upper air setup as depicted by various reliable global models from here on out is very favorable for a lot of intensification. Given how little interaction this will have with Cuba and the remaining amount of time over water, a major hurricane landfall is becoming a very real possibility. I expect Isaac to take it's time organizing its inner core over the next 24 hours, and I don't expect RI to occur until at least it clears the Florida Keys.

As the NHC pointed out, if a well developed core can materialize, then this could be off to the races.....if this takes its time in doing so, it may actually be a bad thing for the N.O.- Panama City area, from the aspect of limited the time up to any intensification halting. eye wall restructuring.

Getting caught up to speed after a couple day vacation. Looks like the models are still a bit inconsistent wrt LF position. I'm still not jamming on the idea that there is going to be any "driving" mechanism to bring this northward in an expedient fashion.

I mentioned a stall or "quasi-stall" a coupled days back....anytime that is implied in the models there is larger uncertainty as to ultimate path/LF point.

Not going too gung ho yet about this being a slam dunk "biggie"....but as you mention...there are some seemingly decent signals that are emerging that we may be dealing with a storm that ends a long drought of US LF'ing majors....

[turtlehurricane]

The recon plan did have a dropsonde with 47kt at the surface at 4:21 this afternoon, shortly before the 5pm advisory, which had a splash point roughly 40 miles from where recon fixed the center at 5:14 this afternoon, which at least at that point in time seems to justify the 5pm intensity of 50kt.

Yup, that area of winds 50 miles to the NE of the center on the pass before the last pass is what they cited in the discussion, flight level was 60 mph in the same area. On the pass after that in the same quad the winds were only 30-50 mph and the strongest winds were 100 miles to the NW. Hence why I think it's been more sporadic wind than the true wind field so far as far as 60 mph winds go. I'd estimate the max wind speed associated with the vortex itself is 50 mph based on that last pass.

[Hurriplane]

Tropical Storm ISAAC Forecast Discussion

WTNT44 KNHC 260244

TCDAT4

TROPICAL STORM ISAAC DISCUSSION NUMBER 20

NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012

1100 PM EDT SAT AUG 25 2012

SATELLITE AND RADAR DATA FROM CUBA SHOW THAT ISAAC IS MOVING

PARALLEL TO...BUT OFFSHORE OF...THE NORTHERN COAST OF CUBA.

THE HURRICANE HUNTER AIRCRAFT DID NOT FIND ANY STRONGER WINDS

DURING THE LATTER PORTION OF THE FLIGHT AND THE INITIAL WIND

SPEED REMAINS 50 KT. HOWEVER...THUNDERSTORM ACTIVITY HAS

INCREASED IN A BAND TO THE NORTH AND EAST OF THE CENTER DURING

THE PAST FEW HOURS AND ISAAC MAY BE ON THE VERGE OF STRENGTHENING.

THE NEXT RECONNAISSANCE FLIGHT IS EXPECTED TO BE IN THE CYCLONE

AROUND 0600 UTC.

THE INITIAL MOTION ESTIMATE IS 305/15 KT. ISAAC SHOULD CONTINUE ON

A WEST-NORTHWESTWARD TO NORTHWESTWARD MOTION DURING THE NEXT 24

HOURS OR SO BETWEEN A LARGE LOW/MID-LEVEL LOW PRESSURE SYSTEM OVER

THE NORTHWESTERN CARIBBEAN SEA AND A MID-LEVEL RIDGE OVER THE

WESTERN ATLANTIC. THE MODEL GUIDANCE IS TIGHTLY CLUSTERED DURING

THIS TIME AND SHOWS A TRACK OVER THE STRAITS OF FLORIDA AND NEAR OR

OVER THE FLORIDA KEYS. IN ABOUT 48 HOURS...ISAAC WILL BE NEARING

THE WESTERN PORTION OF THE RIDGE AND SHOULD MOVE IN A GENERAL

NORTHWESTWARD HEADING OVER THE EASTERN GULF OF MEXICO...BUT LARGE

DIFFERENCES EXIST BETWEEN THE LATEST ECMWF AND GFS MODELS AFTER

THAT TIME. THE ECMWF RECURVES ISAAC AHEAD OF A MID-LATITUDE

TROUGH OVER THE EASTERN UNITED STATES...WHILE THE GFS SLOWS ISAAC

DOWN AS THE TROUGH BYPASSES THE SYSTEM AND THE MODEL THEN TURNS

THE CYCLONE WESTWARD TO THE SOUTH OF A DEVELOPING MID- TO

UPPER-LEVEL RIDGE. THIS BIFURCATION IS ALSO SEEN IN THE MOST RECENT

ECMWF AND GFS ENSEMBLES WITH ABOUT AN EQUAL NUMBER OF MEMBERS

SHOWING RECURVATURE VERSUS A CONTINUE NORTHWESTERLY TRACK TOWARD

THE NORTHERN GULF COAST. SINCE THE UNCERTAINTY IS LARGE AND EITHER

OF THESE SCENARIOS ARE POSSIBLE AT THIS TIME...THE NHC FORECAST IS

LIES BETWEEN THEM. THE UPDATED TRACK IS VERY CLOSE TO THE PREVIOUS

ADVISORY THROUGH 36 HOURS. AFTER THAT TIME...THE TRACK HAS BEEN

ADJUSTED WESTWARD...BUT IT REMAINS EAST OF THE DYNAMICAL MODEL

CONSENSUS TO RETAIN SOME CONTINUITY WITH THE PREVIOUS FORECAST.

THE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO BECOME MORE CONDUCIVE FOR

STRENGTHENING DURING THE NEXT COUPLE OF DAYS AS ISAAC MOVES OVER

THE WARM WATERS OF THE FLORIDA STRAITS AND EASTERN GULF. STEADY

STRENGTHENING IS EXPECTED AND ISAAC IS EXPECTED TO BE AT OR NEAR

HURRICANE STRENGTH WHEN THE CENTER REACHES THE FLORIDA KEYS.

ADDITIONAL STRENGTHENING IS LIKELY WHILE THE CYCLONE MOVES OVER THE

EASTERN GULF OF MEXICO. THE NEW INTENSITY FORECAST IS A LITTLE

HIGHER THAN THE PREVIOUS ADVISORY AND IS BETWEEN THE SHIPS/LGEM

GUIDANCE AND THE MORE AGGRESSIVE HWRF MODEL.

IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK SINCE

SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER. SINCE LARGE

UNCERTAINTIES REMAIN IN THE EXTENDED PORTION OF THE FORECAST...IT

IS TOO EARLY TO DETERMINE EXACTLY WHERE AND WHEN ISAAC WILL MAKE

LANDFALL ALONG THE GULF COAST.

FORECAST POSITIONS AND MAX WINDS

INIT 26/0300Z 22.1N 77.2W 50 KT 60 MPH

12H 26/1200Z 23.4N 79.4W 55 KT 65 MPH

24H 27/0000Z 24.6N 81.8W 65 KT 75 MPH...NEAR FLORIDA KEYS

36H 27/1200Z 25.8N 83.7W 75 KT 85 MPH

48H 28/0000Z 27.2N 85.2W 85 KT 100 MPH

72H 29/0000Z 29.5N 86.5W 90 KT 105 MPH

96H 30/0000Z 31.5N 86.5W 50 KT 60 MPH...INLAND

120H 31/0000Z 34.0N 86.0W 25 KT 30 MPH...INLA

[PSUBlizzicane2007]

I will caution everyone on taking the 00Z early cycle guidance too seriously. That west jump is a direct response to the 18Z GFS west jump. Early cycle guidance uses the previous run's data and extrapolates it. This is why I don't take early cycle guidance too seriously, and why I think posting it without proper explanations is fairly irresponsible. The 00Z GFS can just as easily shift eastward from its 18Z run, and it likely will.

[EasternUSWX]

This is a bad post. Maximum sustained winds means maximum sustained winds. It doesn't mean pick a lower value just so it matches satellite appearances.

Agreed and looked at mission and seen plenty of higher winds nearer the center and not 100 miles away.

This one was 48 miles NE on final pass

Time: 22:56:30Z

Coordinates: 21.8667N 75.7833W

Acft. Static Air Press: 842.7 mb (~ 24.88 inHg)

Acft. Geopotential Hgt: 1,492 meters (~ 4,895 feet)

Extrap. Sfc. Press: -

D-value: -

Flt. Lvl. Wind (30s): From 142° at 45 knots (From the SE at ~ 51.7 mph)

Air Temp: 15.1°C* (~ 59.2°F*)

Dew Pt: -*

Peak (10s) Flt. Lvl. Wind: 46 knots (~ 52.9 mph)

SFMR Peak (10s) Sfc. Wind: 59 knots (~ 67.8 mph)

SFMR Rain Rate: 34 mm/hr (~ 1.34 in/hr)

(*) Denotes suspect data

There were a lot of plots like this and some higher too. 50KTS seems like a good number for now. Plus they had limited fly space due to cuba.

[dan88]

Agreed and looked at mission and seen plenty of higher winds nearer the center and not 100 miles away.

This one was 48 miles NE on final pass

Time: 22:56:30Z

Coordinates: 21.8667N 75.7833W

Acft. Static Air Press: 842.7 mb (~ 24.88 inHg)

Acft. Geopotential Hgt: 1,492 meters (~ 4,895 feet)

Extrap. Sfc. Press: -

D-value: -

Flt. Lvl. Wind (30s): From 142° at 45 knots (From the SE at ~ 51.7 mph)

Air Temp: 15.1°C* (~ 59.2°F*)

Dew Pt: -*

Peak (10s) Flt. Lvl. Wind: 46 knots (~ 52.9 mph)

SFMR Peak (10s) Sfc. Wind: 59 knots (~ 67.8 mph)

SFMR Rain Rate: 34 mm/hr (~ 1.34 in/hr)

(*) Denotes suspect data

There were a lot of plots like this and some higher too. 50KTS seems like a good number for now. Plus they had limited fly space due to cuba.

That particular SFMR reading is likely invalid because of the heavy rainfall rate of 34mm/hr

[wxsmwhrms]

Let me be clear, this is NOT a post about the NAM for tropical forecasting. I was going to mention, though, that it has trended higher with the heights over the SE and Gulf at 72 hours and weaker with the trough moving into the NE US. Just something to watch.

[jasons]

This times one thousand.

This is what I meant two days ago by 'splitting hairs'. Seemed like people were already making LF calls (US) when we were't even sure yet if Isaac would hit or miss the shredder....

[Dsnowx53]

This times one thousand.

Glad to see we're still on the same page.

[masswinter]

The 60 mph winds that NHC is using to define Isaac's intensity are over 100 miles from the center, winds anywhere near the center on the recent pass are 30-50 mph. This has been the case all day, the strongest winds are in the easterlies north of the storm since that's the part that's been over water, and the wind pattern has been sporadic bursts more than truly organized. I think it's a bit dishonest to keep Isaac as a strong tropical storm all day as if it hasn't weakened... especially given the lack of convection and tenuous sfc circulation most of the day.

It is finally gaining convection near the center but its got a long way to go before it can ever reasonably called a hurricane. I don't disagree with the NHC forecast that much since it makes sense that it could become a cane by the time it enters the Gulf, but I don't see the reason for hurricane advisories in South Florida besides a watch in the lower and middle keys. It's not like hurricane force winds are going to be over a broad area immediately when it crosses the hurricane threshold, only a small region will see that.

I'm not going to agree or disagree with you with regards to the issued warnings...rather just point something out. The NHC produces a graphic of hurricane force wind speed probabilities. These probabilities max out around 10% on the Florida coast. By definition a hurricane warning is issued when hurricane conditions are expected. To me 10% is not expected...maybe 50 or 60%? Does anyone else see an inconsistency here? Again, I'm not saying the warnings should not be in place....just trying to understand if and why this inconsistency exists. Maybe I'm missing something....but I could see how this could be confusing to the public.

[WeSuck]

GFS at 63 hours is just south of New Orleans slowing down... Sticking to its guns

EDIT: Pretty much stalls over New Orleans through 72 hours so far

[janetjanet998]

00z gfs west

over MS delta at HR 72 moving slow

[Derecho!]

Well, so much for the GFS coming back east... it's a bit WEST of 18Z.

[Superstorm93]

Well, so much for the GFS coming back east... it's a bit WEST of 18Z.

Yeah, it actually is west of the 18z.

Wonder if the ECM will come back west...

[janetjanet998]

[EasternUSWX]

LA is completely creamed this run. New orleans gets the worst side for like 24 hours. almost craws along the shore.

[Dsnowx53]

Not surprising at all. I only looked at 500mb, but that level shows nothing which would pull this northward quickly. The west camp is looking better and better...

[WeSuck]

From 63-81 hours so far it just literally sits on Louisiana's beaches.

EDIT: By hour 90 it is over western Louisiana shoreline.

EDIT 2: Goes from only NO to TX/LA border on the beach between 66-102 hours. WOW!

[Superstorm93]

Crawls just inland along the LA/TX coast from 72-102 hours

A little further south and we're talking about a N-GOM stall/crawl.

[Dsnowx53]

We are not too far away from the 12z Euro solution from Thursday, to be quite honest.