ATL: ISAAC - Models

[Wx_Warrior]

Gut tells me a trend west is coming tonight with 0z models.

[brunota2003]

I'm pretty sure most of the sondes made it into the 00Z...not sure about all of them, but a good portion should of at least.

[Jevo]

0z NAM +36

[Hurricane Andrew]

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0z Predictions
GFS: A touch west with both landfalls, with first landfall in extreme SW FL, and second in AL.
ECMWF: About the same.
HWRF: A touch east, MS/LA border final LF. First LF the same.
GFDL: A touch east with final landfall, first LF the same.

[jeff]

WV loop of the northern hemisphere showing the trough dropping south out of Alaska towards the west coast to what should be to pump a ridge across the midwest which should induce more trough on the east coast. How exactly all the features react will help guide Isaac.

WV loop: http://wxweb.meteostar.com/models/noaap ... UMBLOOP=10

Ah yes...very good....you are looking in the right place. Question is does it dig down pumping the ridge or dig and then shear out...some of the latest 18Z runs shear the trough out with the central plains ridge more ENE and expansive in a more zonal pattern than amplified.

ok, jeff, for this dummy here, what does that mean ?

The key to the final track and landfall of Isaac is with that trough heading down toward the PAC NW. A deeper and slower trough builds or amplifies the southern plains ridge and digs a downstream SE US trough pulling Isaac NW then NNW...a weakly defined omega pattern. However if that same NW PAC trough digs only some and then moves quickly ENE into the N Rockies and Canada the downstream ridge expands ENE out of the SW US and does not dig as deep of a downstream SE US trough..ie more ridging north of Isaac and the more westward path. I would really like to see these models hold a good consensus for 2 full runs (They had a good consensus lat evening at 00Z and this morning at 12Z, but 18Z has gone back to the shifting around, we need to see if that was a fluke and what the 00Z brings.

[Wx_Warrior]

If Isaac continues to just drift around, models will have to trend west. Storm speeds up, models stay east.

[jeff]

Need a Promet for this question.... If Im trying to look at upper air patterns that steer a storm... is that at the 500mb level or 850mb level?

It depends on the storm intensity...weaker system (weak TS) are steered more by the low level flow (850mb or below) while stronger systems (strong TS or hurricane) you want to look at the 700-200mb steering...or the 700/500/300mb charts out in time.

TY Jeff. Im pulling the 850mb charts for this NAM run.. Should I start using the 500mb at this point?

Need to look at the 500 and 300mb for the forecast...Isaac is a deep enough system.

[Jevo]

0z NAM +42

[jeff]

WV loop of the northern hemisphere showing the trough dropping south out of Alaska towards the west coast to what should be to pump a ridge across the midwest which should induce more trough on the east coast. How exactly all the features react will help guide Isaac.

WV loop: http://wxweb.meteostar.com/models/noaap ... UMBLOOP=10

Ah yes...very good....you are looking in the right place. Question is does it dig down pumping the ridge or dig and then shear out...some of the latest 18Z runs shear the trough out with the central plains ridge more ENE and expansive in a more zonal pattern than amplified.

ok, jeff, for this dummy here, what does that mean ?

The key to the final track and landfall of Isaac is with that trough heading down toward the PAC NW. A deeper and slower trough builds or amplifies the southern plains ridge and digs a downstream SE US trough pulling Isaac NW then NNW...a weakly defined omega pattern. However if that same NW PAC trough digs only some and then moves quickly ENE into the N Rockies and Canada the downstream ridge expands ENE out of the SW US and does not dig as deep of a downstream SE US trough..ie more ridging north of Isaac and the more westward path. I would really like to see these models hold a good consensus for 2 full runs (They had a good consensus lat evening at 00Z and this morning at 12Z, but 18Z has gone back to the shifting around, we need to see if that was a fluke and what the 00Z brings.

[BigB0882]

Looks like the NAM is moving it pretty much due West after barely getting off the North coast of Cuba. Not that you should focus on TC movement with the NAM but it certainly says something about the ridging, right?

[Jevo]

0z NAM +45 (Little alley opened there)

[BigB0882]

So we go from stronger ridging to an opening weakness in 24 hours? Things change so quickly with the weather!

[SouthFLTropics]

That 45 hour NAM is very interesting...Sure would like to know if the G-IV dropsonde data made it into this run. I know it's the NAM but last night it set the tone for the rest of the models.

SFT

[CYCLONE MIKE]

So what is your gut telling you Jeff? 18z a fluke or expect to see some shifts back to the west overnight? Gut is telling the trough will end up not digging as deep to influnece a due north motion. Maybe nw with some wnw mixed in but not as drastic as due north. And what about the stall along the coast after final landfall. A fluke or something we really need to be concerned about?

[Hurricane Andrew]

0z NAM is furthur off the coast of SW FL than the GFS, and slower.

[xcool22]

15 dropsonde in nam models

[thetruesms]

0z NAM +45 (Little alley opened there)

[img]http://img833.imageshack.us/img833/1270/nam2212012082500f45relv.png[img]

Rather than the height/vort image, you may want to show the height/winds image. The wind flow at 500 can sometimes give you a ballpark idea of the steering, as well. Granted, it's not perfect (and sometimes not very good), and you'd rather get a mean wind through the steering layer. But, in a pinch when there isn't much shear, the 500 winds could give you a general idea of steering flow here.

[Jevo]

0z NAM +54 (Alley closing)

[BigB0882]

Does the NAM show it falling apart on the 54 hour map? Probably not the thing to focus on but interesting....

[deltadog03]

pretty pronounced weakness.....



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