Tropical Storm Isaac, Part 2: Isaac Moving Into The Gulf Of Mexico-Hurricane Warnings For Morgan City, LA/MS/AL & FL Panhandle To Destin, FL

[hm8]

It's interesting to see that the models with the lowest error on intensity forecasts generally are keeping below 60 knts for the next 48 hrs and avg. max intensity is 61 knts at 72 hours. Not saying that they will verify just interesting contrast to the 85 kt forecasts from NHC

Are those models with the lowest error on intensity forecast based on this season, or lifetime score? I'm asking because, up into this point in the season, we haven't really had a good chance for sig. intensification in the GOM to really test a forecast on. Come to think of it, the majority of all tropical cyclones never really have the chance for this, so couldn't it be the case that models that don't go gung-ho on intensification naturally have higher verification scores?

[QVectorman]

Are those models with the lowest error on intensity forecast based on this season, or lifetime score? I'm asking because, up into this point in the season, we haven't really had a good chance for sig. intensification in the GOM to really test a forecast on. Come to think of it, the majority of all tropical cyclones never really have the chance for this, so couldn't it be the case that models that don't go gung-ho on intensification naturally have higher verification scores?

It's the score for just the life of this storm. Over the years I've noticed that individual models end up performing better than others based on the storm. But the models that seem to take the lead so to say end up maintaining the lowest error for the entire storm. I just look at it as a tool to discern which models may have a better handle on the environment during the course of the life of the TC. Usually SHIP is always a contender although I haven't seen it performing too well this season so far.GPMN is the ensemble mean for the GFDL hence it's higher. GPM2 is the 12 hour interpolated version of GPMN. SHFR is the 3 day forecast SHIP intensity model. I don't know you may be on to something, but I'm not sure I haven't seen any seasonal scores for intensity error from year to year. Maybe someone else has.

[Buckeye05]

I would think that the radar presentation would have to improve drastically before we see any kind of really serious intensification. If I am looking at it right, more than half of this thing is dry. Satellite presentation looks way better though.

[wxmeddler]

Watching the radar cloud tops over the past few hours the tops have decreased near the COC for the past few hours. The subtle strengthening continues.

[hm8]

It's the score for just the life of this storm. Over the years I've noticed that individual models end up performing better than others based on the storm. But the models that seem to take the lead so to say end up maintaining the lowest error for the entire storm. I just look at it as a tool to discern which models may have a better handle on the environment during the course of the life of the TC. Usually SHIP is always a contender although I haven't seen it performing too well this season so far.GPMN is the ensemble mean for the GFDL hence it's higher. GPM2 is the 12 hour interpolated version of GPMN. SHFR is the 3 day forecast SHIP intensity model. I don't know you may be on to something, but I'm not sure I haven't seen any seasonal scores for intensity error from year to year. Maybe someone else has.

Gotcha, makes sense. Again my only concern about using a model that has been performing well so far with the storm is that it's environment is about to change rather drastically, and it may be that other models will be more suited to handle it. The fact that the none of the current best performing models so far barely even get Isaac above 60kts may even be a red flag in of itself, as that little of intensification is really tough to imagine even if Isaac runs into shear, upwelling problems, etc.

It'll be interesting to see how it plays out.

[Superstorm93]

I would think that the radar presentation would have to improve drastically before we see any kind of really serious intensification. If I am looking at it right, more than half of this thing is dry. Satellite presentation looks way better though.

Exactly. Convection actually has to wrap around the LLC in order for an inner-core to form.

If we can get an inner-core, intensification should pick up. Not sure how much though, since the environment has become questionable.

[CUmet]

This is a storm that would have potential for TS wind radius around 250-300 miles and hurricane maybe 80-100 in the worst case situation. The good news possibly with Isaac is that even if it does become a major hurricane it may do so late enough that the surge may be lagging a bit much as was the case with Charley in 04 which had nothing even resembling a cat 4 as far as storm surge since the storm had only become a cat 4 hours before landfall.

The storm surge is much more a function of storm size, particularly the RMW and the extent of gale-hurricane force winds than it is of previous 24 hour maximum intensity. The concept of the storm surge having a "memory" of the max intensity, or there being some sort of lag was popularized immediately following the 2005 Gulf hurricanes, but the papers I've read about the topic since then suggest that the effect, if any, is small. For example, Charley had a small surge mostly because its wind field was small and the angle of approach may not have been optimal, not because it underwent RI just prior to landfall.

[Indystorm]

How is the environment questionable? Shear is forecast to relax. ULL moving out of the way. Water is warm and land masses not a concern now.

[turtlehurricane]

How is the environment questionable? Shear is forecast to relax. ULL moving out of the way. Water is warm and land masses not a concern now.

If there wasn't southerly shear and dry air it would be a hurricane already.

[lakeeffectkid383]

8:00 PM EDT Sun Aug 26

Location: 24.1°N 82.6°W

Moving: WNW at 15 mph

Min pressure: 991 mb

Max sustained: 65 mph

[QVectorman]

Gotcha, makes sense. Again my only concern about using a model that has been performing well so far with the storm is that it's environment is about to change rather drastically, and it may be that other models will be more suited to handle it. The fact that the none of the current best performing models so far barely even get Isaac above 60kts may even be a red flag in of itself, as that little of intensification is really tough to imagine even if Isaac runs into shear, upwelling problems, etc.

It'll be interesting to see how it plays out.

Did some looking and found the NHC site with stats. ICON IVCN LGEM and DSHP are the best performers from 2009-2011 but I also added them to the chart for this storm.

Added those models to the forecast. All of them cluster at the top with the 88kt peak at 60 hrs along with ramping up intensification this evening.

[CUmet]

Not saying this will necessarily undergo RI, although it wouldn't surprise me at all. But all of this "why isn't it intensifying yet?" type of impatience has happened with every significant TC intensification event that has ever occurred in the history of these boards. If Josh exhibited this type of impatience, he would've never pulled the trigger on the Ernesto chase (and he almost didn't). It was always understood among the good mets here that the inner core would take some time to recover from the island hits and the southwesterly shear that is currently decreasing. Nothing about what's happening right now is surprising at all.

[andyhb]

Not saying this will necessarily undergo RI, although it wouldn't surprise me at all. But all of this "why isn't it intensifying yet?" type of impatience has happened with every significant TC intensification event that has ever occurred in the history of these boards. If Josh exhibited this type of impatience, he would've never pulled the trigger on the Ernesto chase (and he almost didn't). It was always understood among the good mets here that the inner core would take some time to recover from the island hits and the southwesterly shear that is currently decreasing. Nothing about what's happening right now is surprising at all.

This post, so much.

Also, nice sunset shot.

[Uncle Bobby]

This is for sure the best radar presentation yet, from 0006Z

[turtlehurricane]

Partial eyewall structure becoming better organized, Doppler velocities still holding at 50 kt though. The incoming diurnal convective max should help convection continue, this could be one of those nights.

[CoastalWx]

Cirrus canopy on the SW side is also slowly getting better with time.

[Midlo Snow Maker]

[Buckeye05]

This is for sure the best radar presentation yet, from 0006Z

Is that clearing in the center the COC? If so, it looks like it is starting to wrap up nicely.

[EasternUSWX]

WNW of Dry Tortugas something is going on with radar. Convection building around a decreasing DBZ field. Also cloud tops are falling off there. IDK if it is the mid level circulation cause the latest recon fix is SE of that. Any mets chime in?

http://radblast-mi.wunderground.com/cgi-bin/radar/WUNIDS_map?station=BYX&brand=wui&num=1&delay=15&type=N0R&frame=0&scale=0.287&noclutter=0&t=1346026611&lat=0&lon=0&label=you&showstorms=0&map.x=400&map.y=240&centerx=675&centery=379&transx=275&transy=139&showlabels=1&severe=0&rainsnow=0&lightning=0&smooth=0

[Uncle Bobby]

Is that clearing in the center the COC? If so, it looks like it is starting to wrap up nicely.

Yes and yes.

[turtlehurricane]

I think that clearing is indeed the formative eye, system still isn't totally stacked yet but it looks like it's coming together.

[Uncle Bobby]

WNW of Dry Tortugas something is going on with radar. Convection building around a decreasing DBZ field. Also cloud tops are falling off there. IDK if it is the mid level circulation cause the latest recon fix is SE of that. Any mets chime in?

http://radblast-mi.w...ning=0&smooth=0

I'm finding the talk about low tops a little odd. GRL3 currently features a bunch of tops over 40K feet, and two towers at over 50K.

[calamity]

Here's a better animation with the 8 PM position (24.1°N 82.6°W) superimposed on the image.

[EasternUSWX]

I'm finding the talk about low tops a little odd. GRL3 currently features a bunch of tops over 40K feet, and two towers at over 50K.

I was talking about at the "eye" region. The clouds are thinning.

[Kmlwx]

I'm finding the talk about low tops a little odd. GRL3 currently features a bunch of tops over 40K feet, and two towers at over 50K.

They mean in the "eye" ....You don't want high cloud tops in the the eye itself.

[Ground Scouring]

Verification from CIMSS: 18Z HWRF forecasted the 00Z 250-850 mb mean shear west of Isaac almost perfectly...and in fact was slightly too high in regard to shear values.

[turtlehurricane]

The eye is 20-25 miles due north of the latest recon position, I think it's about to take over so we could see a slight northward jog, small win for chasers hoping for this to go further east to avoid the swamps.

[Sunny and Warm]

Here's a better animation with the 8 PM position (24.1°N 82.6°W) superimposed on the image.

I swear I'm seeing the LLC move rapidly north to a position just SE of the clearing and very close to alignment with the MLC. You can clearly see two rotations occurring in the imagery as they align better.

[CUmet]

Frank Strait did a pretty good unbiased video about why this might only be a category 1 or 2 and not a major hurricane. He also gave reasons why this system might not go through rapid intensification.

http://www.accuweath...rming-but/71045

This guy's reasoning is terrible except for the part about the continental shelf waters. The fact that Isaac has been somewhat of an underachiever for most of its life doesn't have any bearing on its future, because the atmospheric conditions are so different and the vortex structure has undergone much change having traversed parts of two islands. There is dry air around the storm, but how is it going to get into the inner core if there's no shear?

I'll never get those 4 minutes of my life back...

[QVectorman]

Not saying this will necessarily undergo RI, although it wouldn't surprise me at all. But all of this "why isn't it intensifying yet?" type of impatience has happened with every significant TC intensification event that has ever occurred in the history of these boards. If Josh exhibited this type of impatience, he would've never pulled the trigger on the Ernesto chase (and he almost didn't). It was always understood among the good mets here that the inner core would take some time to recover from the island hits and the southwesterly shear that is currently decreasing. Nothing about what's happening right now is surprising at all.

Agree plus, the better performing intensity models have been pretty much echoing this for the past 36 hours so it's not really surprising that intensification hasn't taken place yet...yet, lol.