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

[Derecho!]

GFDL came back east to the Florida Panhandle....

[PatrickSumner]

I wouldn't say windshield wipering. To be honest, the westward shift has strong meteorological basis given the likely building back of the ridge. Minor changes are still likely, but to be honest, I think landfall is probably going to fall in a zone from Houma, LA, to Mobile, AL. And the fact of the matter is, whether we like it or not, NOLA is in that region, and it takes a full 72 hours to properly execute an evacuation. We are about 72 hours out already. If a proper evacuation of NOLA is to occur, it has to start tomorrow, whether we as meteorologists are certain about impacts to the city or not. It's just the way it is unless we want to risk having what happened with Katrina happen again.

For what it's worth, I agree with you. Decisions need to be made...even if the eventual track is uncertain. As the saying goes, "better safe than sorry." I certainly hope and pray New Orleans will miss the brunt of Isaac.

[Superstorm93]

GFDL came back east to the Florida Panhandle....

Interested to see what it's ensembles do.

[HurricaneJosh]

I wouldn't say windshield wipering. To be honest, the westward shift has strong meteorological basis given the likely building back of the ridge. Minor changes are still likely, but to be honest, I think landfall is probably going to fall in a zone from Houma, LA, to Mobile, AL. And the fact of the matter is, whether we like it or not, NOLA is in that region, and it takes a full 72 hours to properly execute an evacuation. We are about 72 hours out already. If a proper evacuation of NOLA is to occur, it has to start tomorrow, whether we as meteorologists are certain about impacts to the city or not. It's just the way it is unless we want to risk having what happened with Katrina happen again.

I hear ya, and to be clear, I wasn't suggesting this was model static. But some funny things have happened in the last day, like the GFS and Euro switching sides, etc. And also, it's rare when any model nails it 72 hr out. I agree with you-- New Orleans needs to mobilize fast-- but I also understand what Thunder Road was getting at.

I should also point out that New Orleans has been hit by hurricanes many times in its history. Before Katrina, there was Betsy 1965, which hit the city directly as a Cat 3-- and they got through it. I just don't think every hurricane in SE LA will necessarily be a Katrina-- even if it's strong.

[CooL]

Euro out to 60 and its a good bit west of the 12z run. But not as far west as the GFS.

Edit: Hr 66 - Just offshore of the western tip of the FL panhandle

[phil882]

Where it should go for now. I understand the point made by Tony but history has shown us that the discussion quickly unravels into nothing but doomsday talk.

Agreed. While there is certainly the thread for a NOLA impact, for the sake of thread, I would prefer to keep the discussion meteorologically based rather than talk about opinions about potential destruction.

ECWMF is rolling in now... will be interesting to see if it trends further west after the GFS has been heading in that direction.

[Superstorm93]

00z ECMWF has Isaac a hair south of MS by 72 hours.

[Dsnowx53]

Euro appears to be just south of the AL coastline at 72 hours, heading for the AL/MS border.

[phil882]

Interested to see what it's ensembles do.

Seems like a rather unlikely solution at this time. Isaac would have to immediately start moving NW from its current position, and that seems unlikely at the ridge continues to build back in.

[Srain]

Where it should go for now. I understand the point made by Tony but history has shown us that the discussion quickly unravels into nothing but doomsday talk.

I tend to agree. Let's keep the New Orleans doomsday talk in the banter thread. We've had some awesome discussions in this thread. Let's keep that it way as we move closer to a US landfall. The banter thread was started for a reason by Adam...

[atownwxwatcher]

From what i have seen thus far the 00 Z GGEM, Nogaps, GFS, HWRF all have New Orleans (LA region) as its target zone.....

[Superstorm93]

Didn't think I would only make it to one center fix, but the satellite blackout is killing me.

Just north of Cuba. Not moving NW or anything crazy...

[Ian]

[Derecho!]

Didn't think I would only make it to one center fix, but the satellite blackout is killing me.

Just north of Cuba. Not moving NW or anything crazy...

It's right in the middle of all the model tracks. Baffled as to what people were posting about it deviating from expectations.

[turtlehurricane]

Lowest 850 geopotential height recon observed on this pass was 1460 m, 10 m lower than last mission, so this might be 1-2 mb stronger than before. They didn't fly through the center either since it's close to the Cuban coast. Looks like it's lost some latitude.

[tornadotony]

I hear ya, and to be clear, I wasn't suggesting this was model static. But some funny things have happened in the last day, like the GFS and Euro switching sides, etc. And also, it's rare when any model nails it 72 hr out. I agree with you-- New Orleans needs to mobilize fast-- but I also understand what Thunder Road was getting at.

I should also point out that New Orleans has been hit by hurricanes many times in its history. Before Katrina, there was Betsy 1965, which hit the city directly as a Cat 3-- and they got through it. I just don't think every hurricane in SE LA will necessarily be a Katrina-- even if it's strong.

I understand where you're coming from. You just can't take chances though. Betsy still killed 76 people and flooded entire neighbors in a similar manner as Katrina did. That's neither here nor there to the Isaac discussion, though.

00z Euro takes Isaac into Mobile sub-960mb. Potent stuff. 00z RAOBS from the US caught the poleward outflow channel for Isaac really well, with a respectable-by-August-standards 55 kt at 250mb at Charleston, SC. Certainly supports the outflow and ventilation we've been seeing thus far. Upper-level conditions seems to be fixin' an interesting future for Isaac.

[deltadog03]

EURO is landfall near PNS and creeps north...near Montgomery at hr 108

[Superstorm93]

Lowest 850 geopotential height recon observed on this pass was 1460 m, 10 m lower than last mission, so this might be 1-2 mb stronger than before. They didn't fly through the center either since it's close to the Cuban coast. Looks like it's lost some latitude.

It's south of the 6z position, but I don't believe that it has actually lost latitude. Steadily paralleling the Cuban coast for now.

Just has to get some convection over the circulation, and a hurricane passing through the straights shouldn't be too far off from reality.

I'm out.

[turtlehurricane]

It's south of the 6z position, but I don't believe that it has actually lost latitude. Steadily paralleling the Cuban coast for now.

Just has to get some convection over the circulation, and a hurricane passing through the straights shouldn't be too far off.

2 am EDT latitude is 22.9 °N, recon says it must be south of 22.75 °N. That corroborates the radar trends.

[Superstorm93]

2 am EDT latitude is 22.9 °N, recon says it must be south of 22.75 °N. That corroborates the radar trends.

"It's south of the 6z position"

My point is, it has not actually lost latitude by having some sort of southerly component.

[dan88]

996mb pressure on drop

[Derecho!]

00z GFDL at 24 hrs

That's what I thought it might be.

GFDL has a weird dual vortex structure at 12 hours (another one to the North) which instantly reforms about halfway in-between at 18 hours, which results in it clipping FL at 24.

[Dsnowx53]

The 00z Euro had more westward extension/influence of the Atlantic ridge, and a bit weaker of a trough compared to the 12z Euro.

It's faster as well. All leading to the west shift.

[tmagan]

06Z Observations

[phil882]

The ECMWF has made one large shift in the 00z run. The upper level low that was expected to shift out into the West Gulf of Mexico is significantly further east over the first 24-48 hours. While this won't be enough to inhibit strengthening, its not nearly as favorable as the GFS 200 hPa solution. A quick glance at the latest water vapor animation suggests that a less progressive 200 hPa low in the Gulf of Mexico is more likely to verify.

[turtlehurricane]

"It's south of the 6z position"

My point is, it has not actually lost latitude by having some sort of southerly component.

Terrain might be inducing a southward component, the green area on the south central cuban coast in this image is a mountain range with 1050 m peaks and higher terrain extends to the coast. The air ascending over the terrain becomes anticyclonic due to conservation of PV, pulling the circulation south since it's at the right spot. This effect could also slow the forward speed.

[turtlehurricane]

18z UW-NMS keeps Isaac a tropical storm until 12 hours after landfall in the middle Florida Keys at hour 30, peaking to strong cat 1 before weakening over shelf waters before landfall near Pensacola at hour 66. http://cup.aos.wisc....nd&hour=Animate

[Derecho!]

Terrain might be inducing a southward component

If there was a southward component that needed explaining (which there doesn't appear to be) I guess that would explain it (a single small plateau on the south side of Cuba isn't much, though).

Given forward speed it's going to be past that tiny range pretty fast.

And honestly in terms of things to induce a wobble the giant convective blob over Andros Island would seem to matter as much.

[turtlehurricane]

Recon finding hurricane force winds (75 mph) at flight level 100 miles from the center, what a strange structure. Big convective burst in that quadrant, but we'll see if it persists.

If there was a southward component that needed explaining (which there doesn't appear to be) I guess that would explain it (a single small plateau on the south side of Cuba isn't much, though).

You can't just ignore the recon data which shows this is a bit south.

[phil882]

I think a better explanation is mainly that the mid-level and low-level centers are once again not vertically aligned. The low-level vortex is feeling the effects of binary interaction with the other low level vortex over the Caribbean, while the mid-level vortex is more influenced by the ese/wnw oriented mid-level ridge. There is also moderate southerly shear over Isaac currently.

While I was pretty optimistic about Isaac's future given the favorable upper level pattern depicted by both the 12z GFS and 12z ECMWF, there is a fly in the ointment. There is a pretty strong upper level low located around 22N 87W. This feature is moving very slowly and will quickly start to disrupt Isaac's outflow if it doesn't start moving eastward. Thus, I don't think we will see much development over the next 12-24 hours given both the center decoupling and this unfavorable position of the ULL. The models ultimately have this same ULL enhancing outflow in the 48-72 hour period, but this will depend on if it can move out of the way in the short term.