ATL: ISAAC - Post-Tropical - Discussion

[Shuriken]

Here's a really awesome Water Vapor Loop and a cool Website @ PSU.

http://www.meteo.psu.edu/~gadomski/SAT_ATL/atlanimwv.html

I see you, and raise you: http://www.atmos.washington.edu/~ovens/ ... nhanced+24

Mwahahahahah....

- - - -

Personal forecast 'til morning: The CDO-ish feature will appear to go stationary and warm, maybe even nearly dying off -- but this is only temporary as the various coalescing centers swirl around a common rotational axis at about 15N. (All the board fan-peeps will groan as their big proto-hurricane appears to fizzle once again.) About 9am EST tomorrow, the surface and mid-level centers complete stacking, and Isaac begins an uninterrupted, and at times rapid, intensification trend.

[Shuriken]

ZCZC MIATCPAT4 ALL
TTAA00 KNHC DDHHMM

BULLETIN
TROPICAL STORM ISAAC INTERMEDIATE ADVISORY NUMBER 8A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
200 AM AST THU AUG 23 2012

...RECONNAISSANCE AIRCRAFT FINDS THE CENTER OF ISAAC IS REFORMING
FARTHER SOUTH...


SUMMARY OF 200 AM AST...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...15.5N 63.5W
ABOUT 265 MI...425 KM SE OF SAN JUAN PUERTO RICO
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...W OR 260 DEGREES AT 20 MPH...32 KM/H
MINIMUM CENTRAL PRESSURE...1003 MB...29.62 INCHES

[ncweatherwizard]

I probably ought not be saying much since I've only looked at some data for only 10 minutes or so. My experience though tells me that not too many storms (granted there will be counter-examples; e.g. 2006 Ernesto) that cross mountainous terrain in the way that the current NHC projection shows actually continue northwest in the manner that the guidance is showing unless a huge gap in ridging is present. Currently, there's weak ridging that extends into the eastern GOM, and mid-level ridging is in place over the southern US. If the center were to move over Haiti or Cuba, there would be a fair chance that the LLC and MLC would become decoupled. Then the surface low would have to redevelop, and it would get steered by the low-level flow. If there's even weak ridging in place, that flow would probably favor a more westerly motion than northerly.

Besides, if the thing keeps flying along in the short-term, then we might be focusing on the left side of the guidance envelope anyway. Either way, if I had to bet, I wouldn't put my money on even close to a FL peninsula strike. I've been known to lose bets before.

Scott

[Texashawk]

I swear, every tropical system I've seen this year, especially in the Caribbean, has gone just like this....

http://www.youtube.com/watch?v=Sp3YfmL9RwU

[ROCK]

the reformation delays it arrival into the GOM if that is where it ends up.....still moving west at a fast clip and the steering flow is

http://tropic.ssec.wisc.edu/real-time/d ... oom=&time=

[Shuriken]

In the recon thread, plane's found a potential center at 14.4N -- over a degree south of the last official fix.

-- It appears the old mid-level low is burrowing down to the surface.

viewtopic.php?f=59&t=113392&start=320

(Linking AJC3's pic)

[Caribwxgirl]

If the the centre has reformed further south shouldn't the NHC have adjusted the track even a tad south? I mean i'mnot questioning them saying it will move wnw eventually but that move moment should start from further dont you think? How can the track be exactly the same with such a center shift? I'm confused someone please explain thanks

[Cyclenall]

Personal forecast 'til morning: The CDO-ish feature will appear to go stationary and warm, maybe even nearly dying off -- but this is only temporary as the various coalescing centers swirl around a common rotational axis at about 15N. (All the board fan-peeps will groan as their big proto-hurricane appears to fizzle once again.) About 9am EST tomorrow, the surface and mid-level centers complete stacking, and Isaac begins an uninterrupted, and at times rapid, intensification trend.

Do you mean 9:00 am today (August 23) or literally tomorrow (August 24)? Sometimes people don't remember we're on a new day once it gets late. I would take this seriously as you were spot on with the convection fading and pulsing back up at a certain time a couple days ago, it was very accurate.

If the the centre has reformed further south shouldn't the NHC have adjusted the track even a tad south? I mean i'mnot questioning them saying it will move wnw eventually but that move moment should start from further dont you think? How can the track be exactly the same with such a center shift? I'm confused someone please explain thanks

The NHC doesn't do track adjustments during intermittent advisories so even if the center was 200 miles south, they wouldn't touch it unless a special package came out. They should do something at 5:00 am EDT.

[GeneratorPower]

I'm sure this has been mentioned but I haven't read all 99 pages. The thing that strikes me about this is how freaking huge this system is. It's big. It's taking a long time to spin up, partly because of that. But man, this could be a serious problem for someone given it's size and the fact that entry into the Gulf of Mexico is pretty much assured.

[Shuriken]

I probably ought not be saying much since I've only looked at some data for only 10 minutes or so. My experience though tells me that not too many storms (granted there will be counter-examples; e.g. 2006 Ernesto) that cross mountainous terrain in the way that the current NHC projection shows actually continue northwest in the manner that the guidance is showing unless a huge gap in ridging is present. Currently, there's weak ridging that extends into the eastern GOM, and mid-level ridging is in place over the southern US. If the center were to move over Haiti or Cuba, there would be a fair chance that the LLC and MLC would become decoupled. Then the surface low would have to redevelop, and it would get steered by the low-level flow. If there's even weak ridging in place, that flow would probably favor a more westerly motion than northerly.

Besides, if the thing keeps flying along in the short-term, then we might be focusing on the left side of the guidance envelope anyway. Either way, if I had to bet, I wouldn't put my money on even close to a FL peninsula strike. I've been known to lose bets before.

Scott

Agreed -- exactly happened to Gustov, which was supposed to run up over Haiti into Florida at one point, instead it decoupled over Haiti with the surface low moving southwest around Jamaica, with the eventual track being hundreds of miles farther west.

[ROCK]

they wont have this data in the 06Z run BTW

[Hammy]

moving SSW or so it looks like based on wind plots relative to the last fix--I'm thinking its rotating around whats left of the old center or doing a loop of some sort before resuming a W-WNW motion

[Caribwxgirl]

Personal forecast 'til morning: The CDO-ish feature will appear to go stationary and warm, maybe even nearly dying off -- but this is only temporary as the various coalescing centers swirl around a common rotational axis at about 15N. (All the board fan-peeps will groan as their big proto-hurricane appears to fizzle once again.) About 9am EST tomorrow, the surface and mid-level centers complete stacking, and Isaac begins an uninterrupted, and at times rapid, intensification trend.

Do you mean 9:00 am today (August 23) or literally tomorrow (August 24)? Sometimes people don't remember we're on a new day once it gets late. I would take this seriously as you were spot on with the convection fading and pulsing back up at a certain time a couple days ago, it was very accurate.

If the the centre has reformed further south shouldn't the NHC have adjusted the track even a tad south? I mean i'mnot questioning them saying it will move wnw eventually but that move moment should start from further dont you think? How can the track be exactly the same with such a center shift? I'm confused someone please explain thanks

The NHC doesn't do track adjustments during intermittent advisories so even if the center was 200 miles south, they wouldn't touch it unless a special package came out. They should do something at 5:00 am EDT.

Ok thanks I was really confused.

[Shuriken]

Personal forecast 'til morning: The CDO-ish feature will appear to go stationary and warm, maybe even nearly dying off -- but this is only temporary as the various coalescing centers swirl around a common rotational axis at about 15N. (All the board fan-peeps will groan as their big proto-hurricane appears to fizzle once again.) About 9am EST tomorrow, the surface and mid-level centers complete stacking, and Isaac begins an uninterrupted, and at times rapid, intensification trend.

Do you mean 9:00 am today (August 23) or literally tomorrow (August 24)? Sometimes people don't remember were on a new day once it gets late. I would take this seriously as you were spot on with the convection fading and pulsing back up at a certain time a couple days ago, it was very accurate.

(Thanks.)

Today the 23rd.

(It's puking right on cue, I see.)

...you may be wondering how I came up with that forecast -- answer: my elephantine memory remembers another storm of similar size and strength at-that-point do exactly the same thing in the same vicinity -- Hurricane Gilbert (which also busted every model run for a week straight predicting recurvature...of course they're a lot better these days, but interesting nonetheless).

[Shuriken]

Recon center-fix is due west of Martinique, or about 14.7ish N.

[Cyclenall]

About 9am EST tomorrow, the surface and mid-level centers complete stacking, and Isaac begins an uninterrupted, and at times rapid, intensification trend.

Fits with this:

Prob of RI for 25 kt RI threshold= 55% is 4.3 times the sample mean(12.8%)
Prob of RI for 30 kt RI threshold= 44% is 5.2 times the sample mean( 8.4%)
Prob of RI for 35 kt RI threshold= 32% is 6.3 times the sample mean( 5.0%)
Prob of RI for 40 kt RI threshold= 17% is 5.1 times the sample mean( 3.4%)

Is there a reason recon hasn't found any TS-force winds yet? Is it in the convection where recon hasn't gone yet or something?

[southerngale]

With the latest recon fix at 14.7N, Isaac is further south than it was when it was classified as a TD. So the motion for the past 3 days has been a little south of west.

[meriland23]

my big question is how will this sudden south motion effect the path

[USTropics]

my big question is how will this sudden south motion effect the path

Still a lot of variables to be determined (like if/when Isaac's inner core becomes situated) but if it stays weak and follows the low level steering (i.e. the Euro solution) a track further west is likely. If Shuriken is correct, which seems plausible, and this begins to intensify later this morning at the current center relocation we're looking at less land interaction initially and Isaac would likely feel the weakness in the ridge more effectively, with a path similar to the NHC occurring. I haven't looked at JB's recent thoughts but I'm assuming he has a deepening system also being influenced more by the weakness and heading towards the EC of Florida.

[Shuriken]

my big question is how will this sudden south motion effect the path

Still a lot of variables to be determined (like if/when Isaac's inner core becomes situated) but if it stays weak and follows the low level steering (i.e. the Euro solution) a track further west is likely. If Shuriken is correct, which seems plausible, and this begins to intensify later this morning at the current center relocation we're looking at less land interaction initially and Isaac would likely feel the weakness in the ridge more effectively, with a path similar to the NHC occurring. I haven't looked at JB's recent thoughts but I'm assuming he has a deepening system also being influenced more by the weakness and heading towards the EC of Florida.

I wouldn't be so quick to draw that conclusion.

A track which misses Haiti and eastern Cuba will -- better odds than not this time of season should it wander into the northwestern Caribbean heat-sink -- result in a cat-4 or -5 system (and they usually get that way after a relatively short period of not-forecast explosive intensification) easily capable of modifying its environment in ways the models can't parse from this far out. Storms of that intensity also respond to mean steering different from weaker systems.