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

[thewxmann]

Funny thing, Hispaniola and/or Cuba may be the best thing to happen to Isaac thus far. We may very well see a spike in intensity - as well as a legitimate organization of an LLC - when Isaac crosses the coastline. Frictional convergence might just be the kick that will focus the low-level vorticity within Isaac.

[Superstorm93]

I'm not even sure what the NHC will do with this.

There isn't any evidence of a surface low to the north of this one, so you really can't dispute it. The big question is if they just play everything the same and forecast a sharper WNW/NW movement into Hispaniola, or do they make some rather large changes at 5am. I mean a correction one hundred and ten nautical miles south west of your previous estimate is big.

Based on mid-level winds, this new surface low is still displaced to the east of the mid-level low.

[QVectorman]

Looks like we have a general consensus..

Now my only question is this..

If the center is not located where NHC has it located and it is further south west (as previous microwave image posted seemed to support) .Would this not throw the solutions off of what we are seeing now? What implications would IF it is further SW overall have?

ECM and GFS are in agreement for this first time.

Now we just need a center fix and for the NHC to actually acknowledge it.

Nearly identical with euro and gfs now....I would expect a little nudge right/east for the 5am update....euro crawls this NNE onshore btw...

Looks like that G-IV jet and Hurricane Hunter data ingested for the 0z run certainly helped out the models

[U_Thant]

I said this elsewhere, but the RECON wind presentation has gone from something that looks like it was drawn by my 6-month old daughter to a REALLY, REALLY clean looking one in one short mission.

[Dunkman]

Funny thing, Hispaniola and/or Cuba may be the best thing to happen to Isaac thus far. We may very well see a spike in intensity - as well as a legitimate organization of an LLC - when Isaac crosses the coastline. Frictional convergence might just be the kick that will focus the low-level vorticity within Isaac.

I'd love to hear what the pros think about this. I know the Euro ends up around where the last VDM is and still hits Hispanola but that is one hell of a right turn. It has to go at 306 degrees to just clip the peninsula from here and 322 degrees to clip the mainland of Haiti.

[wxsniss]

Looks like that G-IV jet and Hurricane Hunter data ingested for the 0z run certainly helped out the models

The G-IV and Hunter data included the current mess of vorticity centers, and yet we have relatively good consensus on landfall in the 0Z suite. Perhaps our attempts to identify a COC is not as critical as we think now?

[valkhorn]

I'd love to hear what the pros think about this. I know the Euro ends up around where the last VDM is and still hits Hispanola but that is one hell of a right turn. It has to go at 306 degrees to just clip the peninsula from here and 322 degrees to clip the mainland of Haiti.

That won't be happening. Recall that a sw trend with Katrina changed models significantly. The same will likely happen with Isaac. Just my personal opinion here, but west or WNW is where it's going for a while, and maybe NW, but not N or NNE for days.

[Superstorm93]

I have my own custom RSO loop in GEMPAK which has been running for over three hours now, and I'm really not even sure the convective mass is moving west all that much.

Eager to read the 5am Disco

[thewxmann]

The G-IV and Hunter data included the current mess of vorticity centers, and yet we have relatively good consensus on landfall in the 0Z suite. Perhaps our attempts to identify a COC is not as critical as we think now?

Yeah I was thinking the same thing. Maybe some of the pros can elucidate this for us. Not sure whether the new LLC will just pivot back into the original position, so to speak, or if this is a legitimate change with major implications down the road. Also not sure if all the data captured this development.

[U_Thant]

Yeah I was thinking the same thing. Maybe some of the pros can elucidate this for us. Not sure whether the new LLC will just pivot back into the original position, so to speak, or if this is a legitimate change with major implications down the road. Also not sure if all the data captured this development.

Legit if you ask me, the entire swath of RECON HDOB winds looks too good for this not to be.

[HurricaneJosh]

So we think it's at ~15.0N now, based on the VDM?

[U_Thant]

So we think it's at ~15.0N now, based on the VDM?

I do...little doubt to me.

[Superstorm93]

Legit if you ask me, the entire swath of RECON HDOB winds looks too good for this not to be.

Regarding what you said earlier...

The wind field does look much better organized than 12 hours ago. Especially so on the latest pass.

I'm not going to go all out and say it's strengthening, but it does have an expanding cirrus canopy with a new LLC under some heavy convection.

NOAA P-3 mission is en-route

[Scott747]

Going in for another fix before the next advisory....

[Srain]

I'd like to see the second pass to confirm that this is in fact the 'true center'.

[dan88]

Newest microwave, pass done 2.5 hours ago

[HurricaneJosh]

Well, based on that, it's certainly not up near 17N.

[dan88]

For 5am

TROPICAL STORM CENTER LOCATED NEAR 16.1N 70.0W AT 24/0900Z

POSITION ACCURATE WITHIN 40 NM

[HurricaneJosh]

The 5 am EDT forecast has it near Pensacola with winds of 75 kt at Day 5.

[phlwx]

Well, based on that, it's certainly not up near 17N.

beat me to it...i was just going to say there's no way in hell this is near 17 N.

It's also going to be pretty tough to get that sharp NW movement to match the 0z guidance positioning from the EC and GFS by tonight/tomorrow.

[HurricaneJosh]

I get the impression that the 16.1N is a compromise value, because moving it 2 whole degrees S in one advisory would just be too weird.

[HurricaneJosh]

Not sure I agree.

Recon just hit 999mb at 15.08N

Yeah, as I posted just a second ago, I wonder if the 16.1N is a "continuity value".

Interesting how insistent they still are Re: Shredderola landfall, even though it's now halfway past the island and moving due W.

[Scott747]

The disco is going to require some delicate reasoning. Not to mention the movement W at 15.

[Superstorm93]

Check out the 50 knot south-westerly on the other side of the LLC

This has to be a compromise move.

I'll be back later today.

[HurricaneJosh]

Kind of a dry discussion. Just kind of blah.

[dan88]

51kt flight level winds, 46kt SFMR with 6mm/hr rain rate. Some higher SFMR values, however the higher values are all associated with higher rainfall rates and are likely invalid

[phlwx]

Kind of a dry discussion. Just kind of blah.

So...if the system is moving west...they are projecting a more northward component in their forecast track to compensate for the westward "jog". Yin and yang?

INIT 24/0900Z 16.1N 70.0W 40 KT 45 MPH

12H 24/1800Z 17.0N 71.9W 50 KT 60 MPH

24H 25/0600Z 18.8N 74.1W 45 KT 50 MPH

36H 25/1800Z 20.6N 76.7W 45 KT 50 MPH...INLAND

48H 26/0600Z 22.4N 78.9W 45 KT 50 MPH...OVER WATER

72H 27/0600Z 25.0N 82.5W 55 KT 65 MPH

96H 28/0600Z 28.0N 86.0W 65 KT 75 MPH

120H 29/0600Z 30.5N 87.5W 75 KT 85 MPH

.9 N, 1.9 W in first 12 hours

1.8 N, 2.2 W in 12-24

1.8 N, 2.6 W in 24-36

1.8 N, 2.2 W in 36-48

2.6 N, 3.6 W in 48-72

In contrast to 11 PM:

FORECAST POSITIONS AND MAX WINDS

INIT 24/0300Z 16.7N 68.7W 40 KT 45 MPH

12H 24/1200Z 17.5N 70.7W 55 KT 65 MPH

24H 25/0000Z 18.8N 73.1W 45 KT 50 MPH

36H 25/1200Z 20.2N 75.4W 45 KT 50 MPH...INLAND

48H 26/0000Z 21.8N 77.7W 45 KT 50 MPH...INLAND

72H 27/0000Z 24.8N 82.0W 55 KT 65 MPH...OVER WATER

96H 28/0000Z 27.5N 85.5W 70 KT 80 MPH

120H 29/0000Z 30.0N 88.0W 80 KT 90 MPH

.8 N, 2.0 W in first 12 hours

1.3 N, 2.4 W in 12-24

1.4 N, 2.3 W in 24-36

1.6 N, 2.3 W in 36-48

3.0 N, 4.3 W in 48-72

[jconsor]

The dropsondes that NHC mentioned in the 5AM discussion as putting the sfc center further north were released at 15N and 15.3N. So their center location is at best an estimate. Based on satellite loops and earlier dropsondes from NOAA around 0-2z which suggest the 850 mb and sfc centers were much closer to each other, I believe the sfc center is likely closer to 15.5N.

It's curious that no dropsondes have been released in the last 2 hours. Normally in order to fix a center, the recon plane will release a dropsonde as close as possible to the actual center, but this has not happened. Perhaps the recon plane is having some issues (note that with a few exceptions, it isn't transmitting pressure data.)

All the UKMET and ECMWF ensembles show a SW jog through 6z and then a sharp NW turn toward the SW tip of Haiti, but the only way I can see that happening is a reformation of the center. The steering currents do not support more than a gradual turn to the WNW.

[phil882]

Newest microwave, pass done 2.5 hours ago

I don't think I've ever seen a storm with such a discrepancy between the surface circulation and the 850 hPa center. Those centers are almost always co-located irregardless of the the circulations above. However, based on satellite, we might finally be getting the circulations to align as the convection slows down and takes on a markedly more banded appearance. I agree with the models that we should see this shoot to the NW or even NNW as the center finally consolidates, and starts feeling the weakness in the mid-level flow.

Its worth mentioning that the 06z GFS was farther east then the 00z run. Do to the way data assimilation (DA) works, the full benefit of the dropsonde observations from G-IV take several model cycles to really see their full impact (since DA only accounts for adjusting 15-20% of the initial conditions in the model cycle, with the rest primarily coming from previous model output).

One last thought, with the 00z ECMWF that I think is likely. There is a new center relocating further south at 850 hPa. The ECMWF shows this very well taking place where the center briefly drops to 15N or so before quickly cutting back to the NNW to make landfall in essentially the same place at the 12z solution. If this very poleward motion does not pan out, then there is still a shot Isaac misses Hispaniola.

[kwt]

315 motion from now on takes this through the 'flatter' part of Haiti, 305 takes keeps it totally offshore.

Going to be a close call, I agree that it will lift up NW/NNW for a short while as is normal when a strong LLC first forms.