thewxmann Posted August 22, 2012 Share Posted August 22, 2012 This system still appears to be heavily disorganized. To my eyes, it seems like the mid level center passed over the islands, while the actual low level center is approaching Guadalupe. (METAR and radar used) Blame it on the background low-level flow. Hard to get an LLC organized or strong low-level convergence when the 850mb flow is easterly at 20kt. Models caught onto that early. Link to comment Share on other sites More sharing options...
LakeEffectKing Posted August 22, 2012 Share Posted August 22, 2012 12Z GGEM/CMC has shifted way west and now is a lot more in line with other guidance- skims eastern FL with a landfall JAX/SAV then right over me in ATL. Probably not correct, very unusual track to be sure but the key takeaway is that it is now not a big outlier. Also...take note of what it does to Joyce at h+180..appears to slow her down and turn her back westward. Link to comment Share on other sites More sharing options...
icebreaker5221 Posted August 22, 2012 Share Posted August 22, 2012 Looking at the WV imagery, one could easily be fooled into thinking that dry air to the NE of the system is causing the biggest woes. However, TPW suggests the dry air wrapping in from the W is a far greater problem in terms of actually affecting the core of the system. One can also see the advantage of looking at systems from a co-moving (LaGrangian) framework. This is done by simply subtracting the wave's phase speed from the wind field at every point. An earth-relative framework depicts virtually no ingestion of dry air into Isaac (right), while the co-moving framework shows lower TPW air working its way S, SE, and eventually E into the heart of the vortex (left). 00Z GFS analysis (sorry, don't have 12Z yet) with LaGrangian wind vectors depicts the ingestion of dry air nicely. We can see how the LaGrangian wind vectors are nearly parallel to the TPW gradient along the path of the dry air, suggesting significant advection of dry-air. This leads to dry-air entrainment, a large saturation deficit in the core of the storm, and dry convective downdrafts destroying any secondary circulation that is trying to develop. This is what was occurring last night and is still occurring somewhat right now. Note that wind vectors (red) are indicated between the two outer-most closed 700 mb streamlines, as this is a reasonable estimate of the outer-most environment affecting the storm. You can see that the GFS forecast for 00Z today suggests an entirely different situation. Wind vectors are nearly perpendicular to the TPW gradient (again, within the outer-most closed streamlines) and there is significantly less advection of dry air into the center of circulation. Essentially the system has "closed off" and isolated itself from the dry air. An expected decrease in wind shear is certainly a large contributor as to why this becomes possible. I suspect that the GFS is slightly too quick as to when this will occur (00Z tonight seems a bit too soon to me). But I have a feeling that by tomorrow morning we'll see much less dry air infiltrating Isaac, and we should have a hurricane on our hands. [TPW imagery courtesy CIMSS, all other products courtesy Montgomery Research Group.] Link to comment Share on other sites More sharing options...
wxmx Posted August 22, 2012 Share Posted August 22, 2012 Recon fix around 16.1N 60.4W...~1005mb Link to comment Share on other sites More sharing options...
isnice Posted August 22, 2012 Share Posted August 22, 2012 96 hours out, center of low pressure is a good bit south of central Cuba on the ECMWF. Link to comment Share on other sites More sharing options...
Superstorm93 Posted August 22, 2012 Share Posted August 22, 2012 ECMWF is pretty much unchanged through 108 hours. Looks to be holding steady. EDIT: Honestly, the main reason I think that the ECM is staying south is the Lee cyclone that comes off of Hispaniola. Ridging is definitely stronger than the GFS, but that doesn't appear to be as major as the physics of this storm. Link to comment Share on other sites More sharing options...
Srain Posted August 22, 2012 Share Posted August 22, 2012 ECMWF is pretty much unchanged through 108 hours. Looks to be holding steady. Link to comment Share on other sites More sharing options...
Cheeznado Posted August 22, 2012 Share Posted August 22, 2012 Euro coming in- bit of a north/east shift, Keeps it pretty weak but barely avoids Hispaniola and eastern Cuba, over west Cuba at 120. EDIT- a small but significant NE shift by 132- still SW of the other models, but no longer as huge of an outlier Link to comment Share on other sites More sharing options...
Derecho! Posted August 22, 2012 Share Posted August 22, 2012 Recon fix around 16.1N 60.4W...~1005mb Center is still really, really broad though. Link to comment Share on other sites More sharing options...
Superstorm93 Posted August 22, 2012 Share Posted August 22, 2012 Deeper and a bit NE of the 00z by 132 hours. Off of the NW tip of Cuba. Link to comment Share on other sites More sharing options...
Dunkman Posted August 22, 2012 Share Posted August 22, 2012 Center is still really, really broad though. And there are basically no west winds...it looks pretty awful. Link to comment Share on other sites More sharing options...
phil882 Posted August 22, 2012 Share Posted August 22, 2012 Looking at the WV imagery, one could easily be fooled into thinking that dry air to the NE of the system is causing the biggest woes. However, TPW suggests the dry air wrapping in from the W is a far greater problem in terms of actually affecting the core of the system. One can also see the advantage of looking at systems from a co-moving (LaGrangian) framework. This is done by simply subtracting the wave's phase speed from the wind field at every point. An earth-relative framework depicts virtually no ingestion of dry air into Isaac (right), while the co-moving framework shows lower TPW air working its way S, SE, and eventually E into the heart of the vortex (left). 00Z GFS analysis (sorry, don't have 12Z yet) with LaGrangian wind vectors depicts the ingestion of dry air nicely. We can see how the LaGrangian wind vectors are nearly parallel to the TPW gradient along the path of the dry air, suggesting significant advection of dry-air. This leads to dry-air entrainment, a large saturation deficit in the core of the storm, and dry convective downdrafts destroying any secondary circulation that is trying to develop. This is what was occurring last night and is still occurring somewhat right now. Note that wind vectors (red) are indicated between the two outer-most closed 700 mb streamlines, as this is a reasonable estimate of the outer-most environment affecting the storm. You can see that the GFS forecast for 00Z today suggests an entirely different situation. Wind vectors are nearly perpendicular to the TPW gradient (again, within the outer-most closed streamlines) and there is significantly less advection of dry air into the center of circulation. Essentially the system has "closed off" and isolated itself from the dry air. An expected decrease in wind shear is certainly a large contributor as to why this becomes possible. I suspect that the GFS is slightly too quick as to when this will occur (00Z tonight seems a bit too soon to me). But I have a feeling that by tomorrow morning we'll see much less dry air infiltrating Isaac, and we should have a hurricane on our hands. [TPW imagery courtesy CIMSS, all other products courtesy Montgomery Research Group.] Excellent post Will... I completely agree with you, that the main problem is that the mid-level circulation has not been "closed" on the southwestern flank... allowing for the advection of dry air in the mid levels. My only question is that despite this, why is all of the deep convection on both satellite imagery and microwave imagery focused on the southern flank. If there was dry air being ingested from the SW, why is it not resulting in displaced convection to the NE or E of the circulation center? Link to comment Share on other sites More sharing options...
Superstorm93 Posted August 22, 2012 Share Posted August 22, 2012 VDM of 1004 mbs just east of Guadalupe. EDIT: Still poorly define Horribly "defined" circulation. Link to comment Share on other sites More sharing options...
Superstorm93 Posted August 22, 2012 Share Posted August 22, 2012 North of the Yucatan channel by 150 hours and intensifying quickly. This run seems to be a compromise of the 00z ECM and the 12z GFS. Link to comment Share on other sites More sharing options...
Ian Posted August 22, 2012 Share Posted August 22, 2012 North of the Yucatan channel by 150 hours and intensifying quickly. This run seems to be a compromise of the 00z ECM and the 12z GFS. Still drifting NW at 162... 988ish east central gulf. Link to comment Share on other sites More sharing options...
tmagan Posted August 22, 2012 Share Posted August 22, 2012 18Z Observations Link to comment Share on other sites More sharing options...
Dunkman Posted August 22, 2012 Share Posted August 22, 2012 Looks like recon just found the "other" center. How strange...at least there are west winds associated with this one. So basically the actual wind shift occurred 65 miles SE of where the lowest pressure was found. Link to comment Share on other sites More sharing options...
Superstorm93 Posted August 22, 2012 Share Posted August 22, 2012 Very large/strong system in the central Gulf by 174 hours. (Emphasis on strong) Don't want to say it's stalled, but it's really close. Gonna be nice to see those WU plots. Link to comment Share on other sites More sharing options...
CoastalWx Posted August 22, 2012 Share Posted August 22, 2012 Icebreaker that's a nice post and graphics to go along. Hopefully some of the non met enthusiasts were able to pick up on the different ways we have to look at storms. Link to comment Share on other sites More sharing options...
Ian Posted August 22, 2012 Share Posted August 22, 2012 Very large/strong system in the central Gulf by 174 hours. (Emphasis on strong) Don't want to say it's stalled, but it's really close. Gonna be nice to see those WU plots. Starting to head north at 180... should miss LA to east. Contours are too packed to count. Probably near 970? edit: jumps back nw a bit at 186. Link to comment Share on other sites More sharing options...
Cheeznado Posted August 22, 2012 Share Posted August 22, 2012 Euro says watch out New Orleans....The most consistent model recently is actually the UKMET with its just along or barely off the west coast of FL track headed for the panhandle- I think LEK has a very good track, that is pretty much what I am thinking also at this point. Link to comment Share on other sites More sharing options...
biodhokie Posted August 22, 2012 Share Posted August 22, 2012 Hopefully some of the non met enthusiasts were able to pick up on the different ways we have to look at storms. At the risk of admonishment from the mods, I'd like to say this is definitely educational and I'm enjoying reading you guys discuss the storm and thank you guys for keeping the thread going! Link to comment Share on other sites More sharing options...
Ian Posted August 22, 2012 Share Posted August 22, 2012 Euro says watch out New Orleans....The most consistent model recently is actually the UKMET with its just along or barely off the west coast of FL track headed for the panhandle- I think LEK has a very good track, that is pretty much what I am thinking also at this point. Looks like 964 coming into SE LA at 192? Inland or moving inland at 198. Link to comment Share on other sites More sharing options...
Superstorm93 Posted August 22, 2012 Share Posted August 22, 2012 Strong landfall near the MS/LA area by 198 hours. Impossible to tell due to the massive amount of isobars cluttering the area. (Definitely Sub-976mbs) Verbatim: Would be a very bad system for SE LA. Link to comment Share on other sites More sharing options...
LakeEffectKing Posted August 22, 2012 Share Posted August 22, 2012 Euro says watch out New Orleans....The most consistent model recently is actually the UKMET with its just along or barely off the west coast of FL track headed for the panhandle- I think LEK has a very good track, that is pretty much what I am thinking also at this point. Thanks Cheez...hopefully the extra albedo that Isaac creates will be enough to delay/offset AGW by a few days....or at least make up some for the lack of ice up north! Most of the models are consistent in one regard, irregardless of track, and that is a period of slow motion/quasi-stall in the day 6-7 timeframe....somewhere.... Link to comment Share on other sites More sharing options...
LakeEffectKing Posted August 22, 2012 Share Posted August 22, 2012 Link to comment Share on other sites More sharing options...
Ian Posted August 22, 2012 Share Posted August 22, 2012 Link to comment Share on other sites More sharing options...
LakeEffectKing Posted August 22, 2012 Share Posted August 22, 2012 Strong landfall near the MS/LA area by 198 hours. Impossible to tell due to the massive amount of isobars cluttering the area. (Definitely Sub-976mbs) Verbatim: Would be a very bad system for SE LA....and a very very very bad storm for KMOB. Link to comment Share on other sites More sharing options...
LakeEffectKing Posted August 22, 2012 Share Posted August 22, 2012 Link to comment Share on other sites More sharing options...
HurricaneJosh Posted August 22, 2012 Share Posted August 22, 2012 The Euro scenario is very Frederic-ish: weak over the Greater Antilles --> very strong on the C Gulf Coast: Link to comment Share on other sites More sharing options...
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