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

[Superstorm93]

12z ECMWF is way west of the 00z and decently stronger.

I think this is the first time I have seen it moving WNW in the Gulf.

Bomb in the central Gulf by 138 hours.

EDIT: Intense system well south of CLA and moving WNW.

Server crashed

[andyhb]

The 12z Euro has a lot less weakness due stronger ridges and the Central Plains ridge building east...if it becomes the main steering mechanism it would be going towards TX...probably even C/S TX

If it does have stronger steering in the Gulf, it would probably be stronger at landfall, thanks to less time for dry air intrusion and upwelling. The waters near the Texas/LA coast are also boiling...

Nearing landfall as possibly a major in southwestern LA at 168...

[isnice]

Forget the intensity on the Euro- compare the size of the system with the GFS. It's huge!

[Superstorm93]

Texas/Louisiana border by 174 hours

I'd call that a decent shift from Pensacola

[HurricaneJosh]

The 12Z Euro looks very Rita-ish-- the location and angle of approach.

The intensity modeling reminds of Ernie's-- just all over the place.

[wxmx]

The 12z Euro has a lot less weakness due stronger ridges and the Central Plains ridge building east...if it becomes the main steering mechanism it would be going towards TX...probably even C/S TX

Not this run, of course, but my main point is that if it gets under the CP ridge, it's a whole new game.

[jrodd321]

Texas/Louisiana border by 174 hours

I'd call that a decent shift from Pensacola

[Superstorm93]

Verbatim ECMWF: Isaac would have approximately 72 hours to spend in the Gulf over 29-32C temps

ECM ensembles are going to be very interesting.

[Ian]

The 12Z Euro looks very Rita-ish-- the location and angle of approach.

The intensity modeling reminds of Ernie's-- just all over the place.

[N. OF PIKE]

this 12z euro run has me thinkin of going long oil futures

highest winds this first pass i've seen so far is

URNT15 KNHC 231818

AF300 0709A ISAAC HDOB 24 20120823

181000 1526N 06537W 8427 01547 0076 +160 +160 193040 042 033 001 01

181030 1526N 06536W 8432 01544 0075 +160 +160 193041 042 033 001 01

181100 1525N 06534W 8429 01547 0077 +160 +160 197043 044 034 001 01

181130 1525N 06532W 8430 01546 0078 +160 +160 199045 046 034 001 01

181200 1524N 06531W 8429 01547 0079 +160 +160 199046 047 034 001 01

181230 1524N 06529W 8429 01547 0080 +150 +150 198045 046 033 001 01

181300 1524N 06528W 8430 01546 0079 +150 +150 199044 046 033 001 01

181330 1523N 06526W 8428 01551 0080 +160 +160 199042 044 034 001 01

181400 1523N 06524W 8432 01547 0084 +150 +150 196043 044 033 001 01

181430 1522N 06523W 8428 01552 0088 +150 +150 193041 043 032 002 01

181500 1522N 06521W 8430 01552 0086 +150 +150 192039 040 031 000 01

181530 1521N 06520W 8429 01552 0087 +150 +150 193034 037 032 001 01

181600 1521N 06518W 8430 01552 0085 +150 +150 193030 032 032 000 01

181630 1521N 06516W 8429 01555 0089 +150 +150 190031 032 032 001 01

181700 1520N 06515W 8432 01551 0090 +150 +150 189030 032 032 001 01

181730 1520N 06513W 8429 01555 0089 +150 +150 187029 030 029 001 01

181800 1519N 06511W 8430 01553 0088 +150 +150 186029 029 029 000 01

181830 1519N 06510W 8429 01556 0086 +150 +150 184029 030 030 002 01

181900 1519N 06508W 8430 01553 0088 +160 +160 184029 032 031 002 01

181930 1518N 06507W 8432 01553 0091 +150 +150 186033 034 031 003 01

$$

[HurricaneJosh]

Good analog for the 12Z Euro track-- in terms of landfall location and angle of approach:

[wxmx]

Product: Air Force Vortex Message (URNT12 KNHC)

Transmitted: 23rd day of the month at 18:34Z

Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)

Storm Number & Year: 09L in 2012

Storm Name: Isaac (flight in the North Atlantic basin)

Mission Number: 7

Observation Number: 09

A. Time of Center Fix: 23rd day of the month at 17:51:40Z

B. Center Fix Coordinates: 15°39'N 66°26'W (15.65N 66.4333W)

B. Center Fix Location: 193 miles (310 km) to the S (187°) from San Juan, Puerto Rico (USA).

C. Minimum Height at Standard Level: 1,459m (4,787ft) at 850mb

D. Estimated (by SFMR or visually) Maximum Surface Wind: 22kts (~ 25.3mph)

E. Location of the Estimated Maximum Surface Wind: 57 nautical miles (66 statute miles) to the NNW (335°) of center fix

F. Maximum Flight Level Wind Inbound: From 70° at 21kts (From the ENE at ~ 24.2mph)

G. Location of Maximum Flight Level Wind Inbound: 60 nautical miles (69 statute miles) to the NNW (332°) of center fix

H. Minimum Sea Level Pressure: 1004mb (29.65 inHg)

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 19°C (66°F) at a pressure alt. of 1,525m (5,003ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 1,527m (5,010ft)

K. Dewpoint Temp (collected at same location as temp inside eye): 17°C (63°F)

K. Sea Surface Temp (collected at same location as temp inside eye): Not Available

L. Eye Character: Not Available

M. Eye Shape: Not Available

N. Fix Determined By: Penetration and Wind

N. Fix Level: 850mb

O. Navigation Fix Accuracy: 0.02 nautical miles

O. Meteorological Accuracy: 15 nautical miles

Remarks Section:

Maximum Flight Level Wind Outbound: 47kts (~ 54.1mph) in the east quadrant at 18:12:00Z

Maximum Flight Level Temp: 21°C (70°F) which was observed 49 nautical miles (56 statute miles) to the NNW (339°) from the flight level center

[wxsmwhrms]

This is 5 or 6 runs in a row that the ECMWF has shown this system to undergo major strengthening in the Gulf and make landfall somewhere in the central Gulf coast region from LA to MOB, and it has had consistent support from its ensembles. I would say that's a pretty strong signal.

[Cheeznado]

I never trust a model when it swings wildly like the Euro has been recently, still think the most prudent course is to ignore this run. The UKMET has been much more steady, I still think Biloxi to AQQ is the best forecast. Now if the Euro sticks to its guns a few more runs, all bets are off.

[Superstorm93]

First VDM of the mission.

[HurricaneJosh]

This is 5 or 6 runs in a row that the ECMWF has shown this system to undergo major strengthening in the Gulf and make landfall somewhere in the central Gulf coast region from LA to MOB, and it has had consistent support from its ensembles. I would say that's a pretty strong signal.

I never trust a model when it swings wildly like the Euro has been recently, still think the most prudent course is to ignore this run. The UKMET has been much more steady, I still think Biloxi to AQQ is the best forecast. Now if the Euro sticks to its guns a few more runs, all bets are off.

Discuss.

[phil882]

12z Euro is waaay faster after Hispaniola, and a tad left...central plains ridge is flatter, but bridge is stronger(building east, uh oh)...trough is flatter also..

i'd say ridging is a bit more robust hr 96 to 120 lol

wow @ 120 hr position on 12z euro (west shift)

As I have been saying from the beginning... the strength of the mid-level ridging is the driving factor in the medium range with this system. I had mentioned several days back that there doesn't seem to be a major trough influencing the motion of Isaac. With only a ridge as the driving factor, the storm is more likely to track further west. In addition, its a typical bias in the models to be too weak with mid-level ridging, especially over the Atlantic basin. I know many have highlighted the ECMWF has been overzealous with ridges this year in the midwest, but the weakness that was being shown in the GFS was a response to weaker mid-level high over the West Atlantic. If this builds in stronger (like the ECMWF suggests) then it links the gap between the Bermuda high and the high that has been dominating the midwest and we see Isaac continue westward. This solution has been on the table for a while, and now that the model consensus seems to be shifting west, it doesn't seem so farfetched anymore.

Getting the impression from recon that this isn't organizing much at all despite better looks... going to have a hard time becoming a hurricane before hitting Hispaniola, which may be more favorable for Isaac to survive the island since storms with tight inner cores generally have the worst time. I don't think this will organize nearly as fast as the NHC is calling for after it's done with the mountains either, this reminds me of Ernesto 2006.

This is not a good comparison. Ernesto was battling strong southwesterly shear for its entire life in the Caribbean. Isaac's main problem is dry air entrainment, not vertical wind shear. Once this entraining finally dampens as the entire atmospheric column moistens up, we should see the storm intensify. If anything, Isaac's future is brighter now given its initial more southward location.

[Superstorm93]

[Cheeznado]

Discuss.

The Euro went from FL to almost TX in one run, I call that a pretty big change. The UKMET has never wavered really from a AL/ FL Panhandle hit. I am not saying the new Euro track is impossible, but it would be premature to get on board with a LA or even TX landfall until it steadies out on that track and the other models begin to move in that direction as well. One thing I do know, the Republicans can breathe a bit easier now, this is probably not going to come that close to Tampa.

[40/70 Benchmark]

Discuss.

Man, would I take that.....

[Ground Scouring]

It may be worth noting that the E-W elongation of the vector field on the ECMWF suggests the possibility of greater vulnerability to dry-air intrusion from the WNW, particularly given the low precipitation levels and high subsidence over the the south-central Plains in recent months. The possibility of an MCS southwest of the system might also make Isaac more vulnerable to weakening in the last 36 hours before landfall, given its enlarging circulation over the Caribbean and Gulf, as would be expected due to a more southerly track. Records of N-Gulf landfalling TC intensities during Plains drought years might be interesting.

[Srain]

Seems as is we've seen this before except in the long range GFS...

[wxsmwhrms]

The Euro went from FL to almost TX in one run, I call that a pretty big change. The UKMET has never wavered really from a AL/ FL Panhandle hit. I am not saying the new Euro track is impossible, but it would be premature to get on board with a LA or even TX landfall until it steadies out on that track and the other models begin to move in that direction as well. One thing I do know, the Republicans can breathe a bit easier now, this is probably not going to come that close to Tampa.

No, I generally agree with you. My point was just that the EC has been quite consistent in a general sense on two points: a very strong system, and a central Gulf Coast landfall. If you pinned me down to a most likely scenario based on what I see right now, I would generally say somewhere MSY to PAM. It is looking increasingly likely that the primary steering mechanism for this system is going to be the ridge east of FL, and experience tells me that when you have that setup you usually get a central Gulf Coast impact.

[wxsmwhrms]

Overall winds seem a bit more impressive this recon flight than the previous one.

[CUmet]

The 850 mb circulation looks substantially better defined than yesterday based on the strong winds in the east quad, and you can start to see low cloud elements rapidly moving eastward on the visible loops just west/northwest of the new convective tower. The center dropsonde isn't as indicative of a tilted vortex either, although it's doesn't say anything about what's happening above 850 mb. There is still some turning in the mid-levels on visible loops and long range San Juan radar SW of the low-level center, but the vortex appears to have gradually become less tilted today, and I think we are seeing the beginnings of legitimate intensification (finally).

[HurricaneJosh]

No, I generally agree with you. My point was just that the EC has been quite consistent in a general sense on two points: a very strong system, and a central Gulf Coast landfall. If you pinned me down to a most likely scenario based on what I see right now, I would generally say somewhere MSY to PAM. It is looking increasingly likely that the primary steering mechanism for this system is going to be the ridge east of FL, and experience tells me that when you have that setup you usually get a central Gulf Coast impact.

This is my feeling as well. The Euro swung a bit this run, but the overall gist of it has been consistent. I expect it'll windshield wipe a bit over the next day-- so that the next run will come back E-- but the overall vibe is strongly suggestive of a C-Gulf-Coast landfall.

[andyhb]

This is my feeling as well. The Euro swung a bit this run, but the overall gist of it has been consistent. I expect it'll windshield wipe a bit over the next day-- so that the next run will come back E-- but the overall vibe is strongly suggestive of a C-Gulf-Coast landfall.

Either way, regarding overall model trends currently and the way they have trended over the past 24-48 hrs, score a big one for the Euro, considering how much of an outlier it was a couple days ago.

[HurricaneJosh]

Either way, regarding overall model trends currently, score a big one for the Euro, considering how much of an outlier it was a couple days ago.

Well, let's see what actually verifies.

But if this does end up hitting the C Gulf Coast, then, yeah-- it would be a big score for the Euro in what's been a tough season for it.

[LakeEffectKing]

My take is that if the Euro indeed has the mid-level ridging properly modeled out in time, then solutions further west than even what the Euro (and every other model out there) have currently, are NOT off the table.....It's not like we have a massively digging trough that turns Isaac. And with the ongoing drought feeding back into the seasonal propensity to hold strongly onto ridging across the deep south, I wouldn't overlook the potential of Isaac to head back westward, once/if he reaches the GOM.

Definitely agreed with this. If Issac can stay far enough south, it might even feel the effects of the "death ridge" near the southern Plains, and turn much more westerly towards Texas, even. The fact that all the data seems to stall Issac once it hits land is indicative of the lack of a steering flow. There is a weak trough that enters the midwest, which combined with a potential weakness in the Atlantic ridge that Issac could run into once it hits the Gulf, that could turn him northward towards the western Florida Panhandle. But if that is not enough, Issac could bend well back to the west, and hopefully relieve some drought conditions in the southern Plains.

I can see a Track "A" scenario with Issac approaching the western FLA Panhandle area, and a track "B" scenario of it bending much further west. Not sure I see an in-between scenario at this time.

Strongly agree here. I was going to post in response to wxmann's post about the WPAC typhoon and mention the differences in ridging to the north of each storm making them incomparable, but you said it best here already. I really think we might see a virtual collapse of the steering currents once he does get near/in the GOM, which would cause all kinds of track forecast problems.

12z Euro must have read our postings!!

[LakeEffectKing]

Either way, regarding overall model trends currently, score a big one for the Euro, considering how much of an outlier it was a couple days ago.

Can't score anything yet!!! System is still in the E/C Carribean!!!!