ATL: ISAAC - Post-Tropical - Discussion

[tailgater]

They might think it will be a low end Cat 2 because the pressure gradient will increase as that high builds back in, just me spitballing.

[nautical wheeler]

First time poster long time lurker. Amazing what I've learned on the site over the years - especially that there is quite an art to forecasting these things it seems. Some people have a better "sense" for the behavior and interactions of the atmosphere than others. I'm just your everyday weather buff who used to watch TWC for hours as a kid instead of cartoons.

Im from "that Land Mass between New Orleans and Mobile" as CNN continuously refers to Mississippi - yea that area that took the direct hit from Katrina.


Anyway, it looks to me like Isaac is trying its best to fight the dry air as noted by the convection and moisture trying to wrap around, however there is one large pocket of particularly dry air in the NE quad that it needs to "flush out" before it can do any significant strengthening. Overall structure looks quite good beyond the dry air. If it can cycle that out and completely wrap around the center I could see a low end Cat. 2 right before landfall - as is forecast by the NHC - however it's certainly running out of time to do so.

[ncweatherwizard]

Current IR satellite imagery continues to show relatively unimpressive structure. As we've seen through the past 36 hours, there is intense convection in only ~1/2 of the circulation. Yesterday, it's was primarily located in the northwestern 1/2 of the storm. This morning, most of the convection was "lop-sided" to the western 1/2 of the circulation. As of the latest image I've seen, nearly all of the precipitation is located in the southern semicircle. The upper-level anticyclone associated with Isaac is dislocated to the north of the center of circulation, resulting in some ~10 kt northeasterly shear over the center (and more over the western side of the storm). Although current precipitation water satellite data doesn't really suggest much in the way of dry air in the northern half of the storm, Isaac's appearance on satellite through the past couple of days certainly has shown signs of significant dry air entrainment.

So, the question is whether or not conditions will improve. Considering the warm water and "only" 10 kts of deep vertical wind shear, I would have expected to have seen appreciable intensification already if you had asked me a couple of days ago. However, the storm has looked "off" for the past few days, with strange wind structure as observed by recon (a few days ago, it was a very large area of weak winds near the center of circulation -- yesterday it was multiple eddies flying around). The structure of the winds around the circulation has improved and looks more "classic" now, but the lack of much convection in the northern semicircle doesn't bode well for significant intensification. I'm still waiting for the hammer to drop, so to say, and I'm waiting to see a symmetric blowup of convection around the center, but it's uncertain whether that will happen.

The longer Isaac stays in this 50-60 kt sfc peak wind state, the less time it has over water to intensify. Since I'd rather not see an intensifying hurricane slam into southeastern LA or coastal MS, this is probably a good thing. Landfall may not be that far off; each additional hour that recon flies through and sees only 55-60 kt surface winds is one less hour that intensification can occur. We can hope that Isaac maintains status quo of slow intensification and it makes landfall as a Cat 1. Considering the potentially "worst case scenario" track of putting New Orleans in the front right quad of the storm, this is much better than a major hurricane...

Plus, once this gets close to land, it's very likely that the eastern half of the cyclone will entrain dry continental air. It would not completely shock me if there are no measurements of sustained hurricane force winds anywhere when this thing makes landfall, even if it is classified as a hurricane at landfall (See Irene 2011 for an example).

[SouthFloridawx]

Hey Kool Aid Man!
h0ttp://img16.imageshack.us/img16/5741/heykoolaidman.jpg
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I know we aren't supposed to use one-liners, but that's pretty funny!

[EBrads146]

11 PM stays at 70 mph

[PTPatrick]

Still a TS!

[pwrdog]

979mb still 70 mph..

It moved slightly more west than north 0.4 north & 0.5 west..

[tailgater]

Hey Kool Aid Man!



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yeah the shrinks could use Isaac's IR pics instead of ink blots.

[monicaei]

What are y'all thoughts on Isaacs chances, realistically, of achieving hurricane status prior to landfall? Gotta say, he's an underachiever thus far, and I'm pretty thrilled about it!

[fasterdisaster]

I'm guessing they held back on upgrading because of the satellite presentation.

[hurricanes1234]

Imagine this - Isaac is now more intense than Ernesto by 1 mbar and it hasn't even made it to hurricane strength yet. This storm will definitely go down in my book as one of the oddest storms I've tracked yet. And of course, it will be in the same list as Daniel from earlier this year!

[tolakram]

I'm guessing they held back on upgrading because of the satellite presentation.

I did not see any reliable surface wind measurements of hurricane strength or above. Did I miss one?

[JamesCaneTracker]

What are y'all thoughts on Isaacs chances, realistically, of achieving hurricane status prior to landfall? Gotta say, he's an underachiever thus far, and I'm pretty thrilled about it!

IMO when/if he goes he's going to do very quickly... If the winds ever decide to respond to the pressure he will most certainly become a cat 2 Hurricane or greater considering the pressure is already that of a cat 2 and still falling.

Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

[ROCK]

the center is probably migrating to the cold convection tops to the SW some....if that ever wrapped around it would probably shoot more north...I dont doubt the more west than north either....

[tolakram]

What are y'all thoughts on Isaacs chances, realistically, of achieving hurricane status prior to landfall? Gotta say, he's an underachiever thus far, and I'm pretty thrilled about it!

NHC predictions look good to me. I'm hoping it keeps having dry air issues all the way to the coast, but it must be watched since a lot of reliable guidance does show intensification just before landfall.

[jasons2k]

What are y'all thoughts on Isaacs chances, realistically, of achieving hurricane status prior to landfall? Gotta say, he's an underachiever thus far, and I'm pretty thrilled about it!

The NHC says it will be, and it's always good to prepare for at least one category up. Especially in this case, the surge will be a problem. In the end, the story may be incredible flooding since it's such a slow mover.

[rainstorm]

What are y'all thoughts on Isaacs chances, realistically, of achieving hurricane status prior to landfall? Gotta say, he's an underachiever thus far, and I'm pretty thrilled about it!

pressurewise its already a low end cat2.

here is an interesting chart

http://www.weather.com/encyclopedia/cha ... scale.html

979 is a minimal cat2. if the winds catch up withthe pressure it will go up quickly.

[fasterdisaster]

I'm guessing they held back on upgrading because of the satellite presentation.

I did not see any reliable surface wind measurements of hurricane strength or above. Did I miss one?

No, you're right. I should have clarified: the flight level winds combined with the lack of surface winds by themselves meant the NHC could go either way, but the satellite presentation is what convinces them (and me FWIW) that this is still a TS. That's all random conjecture of course.

[rainstorm]

i dont think 960 mb at landfall is out of the question now.

[nautical wheeler]

The moisture envelope around Isaac appears to be improving - the dry air slot is filling in. Better outflow on the southern side of the storm as well. Will Isaac respond though?