ATL: ISAAC - Post-Tropical - Discussion

[ConvergenceZone]

Until Isaac can convince me otherwise, I'm just assuming it will be landfalling as
a tropical storm. Isaac has cried wolf too many times, but nothing ever happened.
If the circulation was small, I'd be all on board with strengthening, but with a
poorly constructed core and organization, I'm not buying the intensification,
but it's always welcome to prove me wrong

[DukeDevil91]

So the strengthing ridge would make it go more west?

yes... depending, of course on how far west the ridge was.

[KWT]

Until Isaac can convince me otherwise, I'm just assuming it will be landfalling as
a tropical storm. Isaac has cried wolf too many times, but nothing ever happened.
If the circulation was small, I'd be all on board with strengthening, but with a
poorly constructed core and organization, I'm not buying the intensification,
but it's always welcome to prove me wrong

It is small, wxman57 said earlier on the wind field is probably smaller than the average, its certainly not a big storm!

I think it will strengthen, how much though seems up in the air, I'd go for 85kts at the moment but given there are still some models bombing towards landfall, it'd be a little unwise ruling anything out now.

[Time_Zone]

UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 27 AUG 2012 Time : 144500 UTC
Lat : 26:04:25 N Lon : 85:15:27 W


CI# /Pressure/ Vmax
3.4 / 986.4mb/ 53.0kt


Final T# Adj T# Raw T#
3.3 3.2 3.2

Center Temp : -61.5C Cloud Region Temp : -58.3C

Scene Type : UNIFORM CDO CLOUD REGION

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : ON
Rapid Dissipation Flag : OFF

C/K/Z MSLP Estimate Inputs :
- Average 34 knot radii : 140km
- Environmental MSLP : 1009mb

Satellite Viewing Angle : 32.5 degrees

[CronkPSU]

Until Isaac can convince me otherwise, I'm just assuming it will be landfalling as
a tropical storm. Isaac has cried wolf too many times, but nothing ever happened.
If the circulation was small, I'd be all on board with strengthening, but with a
poorly constructed core and organization, I'm not buying the intensification,
but it's always welcome to prove me wrong

this is exactly where I am at...everytime I thought for sure it was going to strengthen, it hasn't, the east side of the storm now looks terrible (of course I am going through a feederband in Orlando as I type this but there is just dry air from here to the core basically), I just don't see it doing anything more than the NHS predicts and that may be too strong as well

[wxman57]

Could someone draw a circle on a satellite image to show just exactly where the center is? I'm ''image challenged'' I guess.

Here's a shot from my workstation indicating the center JUST to the east of the east Gulf buoy (989.1mb there).

[Stormtrack]

I could see the hurricane warning for the panhandle being lowered to tropical storm warning later...they are not in the forecast cone any longer and the forecast radius of hurricane force winds based on current forecast is 30 miles to the ne and se of the center. Panhandle will see t.s. conditions unless a major jump north happens.

Also note that part of sw LA in the cone has only a tropical storm watch in effect by comparison. I could see that becoming a ts warning later...

Wow! Looks like N.O. is firmly in the cross hairs. I just hope and pray this thing stays this side of a cat 1 or less. The unfortunate thing is Katrina did her damage there as a low end cat 2. I hope the levees are shored up and the pumps are in good working order.

But Katrina was pushing a Cat4/5 surge. Yeah, it's intensity decreased as it approached landfall, but the surge remained. Post-storm studies shows 20+' surge.

Yes and Ike in 2008, the 2nd costliest hurricane ever, was the same way. High Cat 2 winds at Galveston, but Cat 4 surge.

[CalmBeforeStorm]

Until Isaac can convince me otherwise, I'm just assuming it will be landfalling as
a tropical storm. Isaac has cried wolf too many times, but nothing ever happened.
If the circulation was small, I'd be all on board with strengthening, but with a
poorly constructed core and organization, I'm not buying the intensification,
but it's always welcome to prove me wrong

It is small, wxman57 said earlier on the wind field is probably smaller than the average, its certainly not a big storm!

I think it will strengthen, how much though seems up in the air, I'd go for 85kts at the moment but given there are still some models bombing towards landfall, it'd be a little unwise ruling anything out now.

From the NHC Discussion at 11:00 AM;
THE LACK OF STRENGTHENING APPEARS TO TO BE DUE TO THE
LARGER-THAN-AVERAGE WIND RADII...WHICH HAVE YET TO CONTRACT
INWARD.

[otowntiger]

Until Isaac can convince me otherwise, I'm just assuming it will be landfalling as
a tropical storm. Isaac has cried wolf too many times, but nothing ever happened.
If the circulation was small, I'd be all on board with strengthening, but with a
poorly constructed core and organization, I'm not buying the intensification,
but it's always welcome to prove me wrong

I agree with you and feel the same way at this point. I also hope this to be true for everyone's sake given the forecasted track.

[wxman57]

From the NHC Discussion at 11:00 AM;
THE LACK OF STRENGTHENING APPEARS TO TO BE DUE TO THE
LARGER-THAN-AVERAGE WIND RADII...WHICH HAVE YET TO CONTRACT
INWARD.

The NHC is clearly being a bit cautious with that statement, as it does not agree with their Hurricane Research Division analysis. I think that Isaac IS consolidating now, and the wind field is definitely shrinking to below average. I think that the lack of strengthening is due to a number of factors:

1. Evidence of southerly wind shear tilting the core northward (upper low to its SW)
2. Influx of dry air in the mid levels
3. Layer of warmer air aloft as evident by the current Gulf instability analysis
4. Lower oceanic heat content in the eastern Gulf

I think that Isaac's previously larger than average size may have slowed its consolidation, but that's no longer a factor.

[otowntiger]

From the NHC Discussion at 11:00 AM;
THE LACK OF STRENGTHENING APPEARS TO TO BE DUE TO THE
LARGER-THAN-AVERAGE WIND RADII...WHICH HAVE YET TO CONTRACT
INWARD.

The NHC is clearly being a bit cautious with that statement, as it does not agree with their Hurricane Research Division analysis. I think that Isaac IS consolidating now, and the wind field is definitely shrinking to below average.

Not to nitpik your wording here but if the NHC was being cautious wouldn't they be acknowleding the contraction of wind or does that not mean intensification? It would seem they are downplaying the contraction?
:edit: oh nevermind, I just read your edit addtion at the end regarding the reasons for not intensifying.

[wxman57]

From the NHC Discussion at 11:00 AM;
THE LACK OF STRENGTHENING APPEARS TO TO BE DUE TO THE
LARGER-THAN-AVERAGE WIND RADII...WHICH HAVE YET TO CONTRACT
INWARD.

The NHC is clearly being a bit cautious with that statement, as it does not agree with their Hurricane Research Division analysis. I think that Isaac IS consolidating now, and the wind field is definitely shrinking to below average.

Not to nitpik your wording here but if the NHC was being cautious wouldn't they be acknowleding the contraction of wind or does that not mean intensification? It would seem they are downplaying the contraction?

The NHC's job is to get/keep people out of harm's way. They're not going to say anything at this point to get the general public to take Isaac more lightly. I think that's prudent. Any hurricane is very dangerous. But the are overstating the size component in their advisories - and that's a fact borne out by current analyses, not just my opinion.

[Blinhart]

From the NHC Discussion at 11:00 AM;
THE LACK OF STRENGTHENING APPEARS TO TO BE DUE TO THE
LARGER-THAN-AVERAGE WIND RADII...WHICH HAVE YET TO CONTRACT
INWARD.

The NHC is clearly being a bit cautious with that statement, as it does not agree with their Hurricane Research Division analysis. I think that Isaac IS consolidating now, and the wind field is definitely shrinking to below average. I think that the lack of strengthening is due to a number of factors:

1. Evidence of southerly wind shear tilting the core northward (upper low to its SW)
2. Influx of dry air in the mid levels
3. Layer of warmer air aloft as evident by the current Gulf instability analysis
4. Lower oceanic heat content in the eastern Gulf

So you think it will intensify or not??

What I'm looking at for the large storm is the size of where the storms are. From just off New Orleans, to off the East Coast of Florida, to South of Cuba. That is a large canopy to be wrapped together, so it should take a long time for the winds to catch up to the pressure drops.

[GCRain]

Could someone draw a circle on a satellite image to show just exactly where the center is? I'm ''image challenged'' I guess.

Here's a shot from my workstation indicating the center JUST to the east of the east Gulf buoy (989.1mb there).
http://home.comcast.net/~cgh57/isaac2.gif

Thanks wxman57.That helps a bunch.

[WxGuy1]

I'm surprised that Isaac remains only a tropical storm considering the time it's been over very warm water. I expected disruption and delayed intensification from Cuba and Haiti, but I, and most folks, it seems, expected that the storm would become a hurricane given the very warm water and only light-moderate shear. As I'm sure we all know, we have comparatively less skill forecasting intensity (compared to track). Even if Isaac went through a period of rapid intensification, I think it's quite unlikely it would be any worse than a Cat 2 at landfall. It *could* be worse (Bastardi seems to make sure to mention how it could be worse -- see 960 mb by yesterday or Cat 5 by landfall), but it could also not intensify much further and make landfall as a Cat 1.

Note that the big surge producers tend to (a) be large in size and (b) have come from storm that previously had been Cat 4 or Cat 5. Katrina was only Cat 3 at main landfall IIRC, but it was carrying it's massive surge accumulated from the time it had been a Cat 5. Again, we're not very good with intensity forecasting, so this post gets the usual "caveat emptor" as any other post discussing intensity forecasts.

[ConvergenceZone]

Until Isaac can convince me otherwise, I'm just assuming it will be landfalling as
a tropical storm. Isaac has cried wolf too many times, but nothing ever happened.
If the circulation was small, I'd be all on board with strengthening, but with a
poorly constructed core and organization, I'm not buying the intensification,
but it's always welcome to prove me wrong

It is small, wxman57 said earlier on the wind field is probably smaller than the average, its certainly not a big storm!

I think it will strengthen, how much though seems up in the air, I'd go for 85kts at the moment but given there are still some models bombing towards landfall, it'd be a little unwise ruling anything out now.

KWT, if this is true, why were the NHC discussion writeups yesterday and the weather
channel yesterday stating that due to the large circulation, strengthening
should be slow? What has changed between yesterday and today regarding the
circulation? just curious.

[wxman57]

So you think it will intensify or not??

What I'm looking at for the large storm is the size of where the storms are. From just off New Orleans, to off the East Coast of Florida, to South of Cuba. That is a large canopy to be wrapped together, so it should take a long time for the winds to catch up to the pressure drops.

Yes, it will intensify. Question is, by how much? The tendency through its existence has been to over-forecast the intensity. I think that's probably still the case. Yes, it could reach strong Cat 1 or Cat 2, can't rule that out. However, more likely it will be a lower-end Cat 1 with a tiny area of hurricane force wind NE of the center (that remains mostly over water) at landfall.

[KWT]

KWT, if this is true, why were the NHC discussion writeups yesterday and the weather
channel yesterday stating that due to the large circulation, strengthening
should be slow? What has changed between yesterday and today regarding the
circulation? just curious.

Take a look at Wxman57's post above, it covers it all very nicely. I'd say probably the main factor is the shear which has helped to drive the moderate dry air into the system and really cause that lop-sided look it had this morning. It does seem to have shaken that off to some extent but its still got a way to go.

[wxman57]

KWT, if this is true, why were the NHC discussion writeups yesterday and the weather
channel yesterday stating that due to the large circulation, strengthening
should be slow? What has changed between yesterday and today regarding the
circulation? just curious.

Isaac's general wind field has been rather large, if you consider the whole circulation field (including the outer closed isobar). Yesterday, the tropical storm force winds DID extend out to 200 miles or so at one point, though there weren't TS winds from the center all the way out to 200 miles. As Isaac started developing a core of convection during the day on Sunday, those TS winds began to contract. At current values of around 150 miles northeast and southeast of the center they're just a little about average for all storms since 1988. However, that's VERY large for a tropical storm. Typical radii are closer to about 50-70 miles for a tropical storm. As a tropical storm, its wind field is too spread out for rapid intensification, though it is starting to contract now.

Oh, and I see the 12Z GFS has just about come to its senses and gave up on any mid to SW Louisiana coast hit.

[Smurfwicked]

From the NHC Discussion at 11:00 AM;
THE LACK OF STRENGTHENING APPEARS TO TO BE DUE TO THE
LARGER-THAN-AVERAGE WIND RADII...WHICH HAVE YET TO CONTRACT
INWARD.

The NHC is clearly being a bit cautious with that statement, as it does not agree with their Hurricane Research Division analysis. I think that Isaac IS consolidating now, and the wind field is definitely shrinking to below average.

Now that the wind field is shrinking how long does the increased storm surge from the prior large wind field stay with Issac? Is it safe to assume that given the proximity to landfall that the increased threat of a higher storm surge will still be present even if Issac tightens up to a much smaller wind field?