ATL: DELTA - Post-Tropical - Discussion

[aspen]

Delta is reminding me a lot of 2002 Lili. Fast moving storm that reached its peak in the central gulf before weakening prior to landfall. The increased organization were seeing today already is pretty concerning.

Chances growing this becomes strongest storm of the season

It has 130kt Laura to beat out for that distinction so .

That’s definitely not impossible, and the latest trends make that look more likely. The center reformation has led to a much better structure than expected, as well as a stall in its forward motion that’ll keep it in the ultra-favorable WCar for longer. Assuming no hiccups like random dry air intrusion or an EWRC counter the highly favorable 30C SSTs, extremely high OHC, low shear, and favorable UL pattern, Delta could explode to surpass Laura’s peak and perhaps make a run at Cat 5 status. 48 hours over waters capable of supporting a <890 mbar hurricane with basically nothing to stop it is not a very comforting thing to see.

[Weatherboy1]

Considering that Gamma is going nowhere fast ... and that all the models that had it heading W/WSW to the BOC have failed miserably ... I'd keep a close eye on Delta. If the circulation of Gamma doesn't exit stage right anytime soon, I would expect that to have an impact on the path of Delta. Perhaps lead to an earlier turn to the N and/or the storm not getting as far west as currently forecast. Will have to see how next day or shakes out.

[AutoPenalti]

Looks like the dry slot that was trying to filter in to Delta seems to be clearing out rapidly.

[tolakram]

Visible loop
https://whirlwind.aos.wisc.edu/~wxp/goes16/grb/meso_vis/meso1_60.html

source: https://www.aos.wisc.edu/weather/wx_obs/GOES16.html

[PTrackerLA]

[GCANE]

Looking at CIMSS, the PV Streamer appears to have gotten over the CoC.
These things can be very deceptive.
What appears to be a warm-core feature may in fact be the PVS.
It would put a lid on getting the vorts stacked.
A lot of convection firing around this though.
Usually takes about 12 hrs or so for it to shake out.
Once the PVS goes, that trof to the east would likely setup a good poleward outflow channel.

[HurricaneAndre2008]

11:00 AM EDT Mon Oct 5
Location: 16.4°N 78.6°W
Moving: W at 7 mph
Min pressure: 1002 mb
Max sustained: 45 mph

[NXStumpy_Robothing]

Going off of purely convective trends, it seems like the system is wanting to consolidate further SSW than may have been initially forecasted. Such a scenario, were it to actually pan out, has some interesting implications on the future track and strength of TD26/Delta.

<Snip>

However, such a scenario also leads to a slightly more unfavorable environment in the mid-term (post-Cuba until Gulf landfall):
1) A storm that is on the southern edge of the cone would be sheared more by the outflow of Gamma as it approaches and passes through the Yucatan Channel;
2) This track would also be more prone to the steering influence of Gamma, which could drag it further westward before it's allowed to move north;
3) It's displaced further from the anticyclone that is forecast to establish itself in the eastern Gulf of Mexico;
4) Such a location could allow the southwesterly flow aloft in the western Gulf of Mexico to disrupt the core of the system more, which could induce a greater weakening trend as it approaches landfall.

<Snip>

Solid post.

One thing I will add is that IMO #1 and #2 are pretty much non-issues now, since Gamma has become completely decoupled. There is (and likely will be) little to no outflow generated by Gamma itself anymore. The larger (synoptic scale) 200mb ridge is much more dominant and is soon to be very favorably cololated with the center of TD 26/Delta as it moves WNW, while Gamma continues to find itself in hostile (and at best marginal in the future) enviromental conditions for the remainder of its existence. And while there will be some binary interaction between the two cyclones once 26/Delta approaches, Gamma will only become weaker/shallower, while 26/Delta becomes vertically deeper and much stronger. This will likely make 26/Delta the more successively dominant steering influence in terms of binary interaction between the two cyclones.

Hey, just catching back up on this thread/reply. You're right on pointing out how the first two points have been close to nullified thanks to Delta's organizational trends and Gamma's lack of well... much of anything, really. However, wouldn't Gamma still impart a mild amount of shear at the low to mid-levels? This probably would not have much of an impact on Delta (if it organizes a strong inner core like it appears to be doing so), but it might be worth seeing if it serves as a bit of an inhibitor on Delta's potential as it approaches Cuba.

In terms of Gamma pivoting Delta westward, such a scenario seems to be getting further and further unlikely. Although, it must then be wondered why this morning's runs have shifted westward regardless...

[kevin]

Part of the new NHC discussion:

"Delta is forecast to traverse very warm waters over the northwestern
Caribbean Sea and be in a very low vertical wind shear environment
during the next couple of days. These conditions should allow for
significant strengthening during that time, and the NHC intensity
forecast is at or above the various intensity aids. It is somewhat
surprising that the intensity aids were generally a little lower
this cycle, but the expected low shear and SHIPS rapid
intensification index support the higher than climatological rate
of intensification. After 72 hours, increasing southwesterly shear
and the cooler shelf waters over the northern Gulf are likely to
induce some weakening later in the period. The updated NHC
intensity forecast calls for a faster rate of intensification over
the next 48-60 hours, but is similar to the previous advisory
thereafter.

FORECAST POSITIONS AND MAX WINDS

INIT 05/1500Z 16.4N 78.6W 40 KT 45 MPH
12H 06/0000Z 17.1N 79.6W 50 KT 60 MPH
24H 06/1200Z 18.7N 81.7W 60 KT 70 MPH
36H 07/0000Z 20.8N 84.3W 75 KT 85 MPH
48H 07/1200Z 22.8N 86.8W 85 KT 100 MPH
60H 08/0000Z 24.6N 89.1W 90 KT 105 MPH
72H 08/1200Z 26.0N 90.7W 90 KT 105 MPH
96H 09/1200Z 28.8N 91.1W 85 KT 100 MPH
120H 10/1200Z 33.1N 88.2W 40 KT 45 MPH...INLAND"

[cp79]

Speed is going to be important because it does seem like a trough will pick it up long term and push it NE. When that happens, I don’t know. Some want to do it before it makes landfall and some after. Its slow movement this morning may support the Ne turn before land, but timing will be everything.

[Steve]

I wish no one would have to deal with this but I have to say I'm encouraged that Michael affected areas are not likely to be impacted much, if at all by Delta if the current trends continue...

Hopefully. I'm not saying you did, but I personally wouldn't slam the door on Panama City. While the current cone runs to Walton?Bay County on its eastern extreme, cone of uncertainty could have an eastern periphery another 100-150 miles east (or west) in the next 3-4 days. Models are pretty tightly clustered, but we all know the later in the season it gets, the more likely Gulf systems would be on the easterly side of a potential threat area (this is NOT 100% ). Just the same, there looks to be a push from the east in the Atlantic almost guaranteeing that there's some point along the Panhandle that would be too far east for it to get to. Look at Water Vapor:

Water Vapor
https://cdn.star.nesdis.noaa.gov//GOES1 ... 00x540.gif


Now run (press the play button) the GFS @ 500mb. This is easy to match up with the Water Vapor as you can see the ridging across Florida from the W Atlantic not relenting. This ridging (looks like a mid-upper level finger ridge) is clearly the feature that will direct Delta NW for a while before rounding the western periphery. BUT, down the line, the GFS has sort of backed off on the approaching long wave that was set to follow Delta by a couple of days. Now a small buckle (a really shortwave) picks it up and directs it out. The upper trough/longwave now lifts up and out after Delta does, so now there really isn't a large scale continental trough that can push it up farther east more quickly.

GFS @ 500mb
https://www.tropicaltidbits.com/analysi ... 00506&fh=6

If things stay as they are, we can narrow the expected landfall area almost to Morgan City to Navarre Beach and should be able to further hone it in as the week goes on. But again for now, there's no way Panama City should be considered out of the woods IMHO.

[StPeteMike]

The slow movement west with little gain in latitude is concerning. Makes a NE turn before land more possible. Good news for the Cajun State, bad news for areas impacted by Sally.

[us89]

If the track holds, we will get some rain from this in Atlanta, and it will be our fifth tropical impact this season - after Marco, Laura, Sally, and Beta.

[Steve]

Part of the new NHC discussion:
96H 09/1200Z 28.8N 91.1W 85 KT 100 MPH

91.1W for now is the western periphery of the track. If you draw a line to the Gulf Coast, that's roughly around Amelia, LA (oil & gas, shipping area) which is a hair east of Morgan City and a bit west of Houma/Cocodrie.

[Kazmit]

Looking at least 55kt already, IMO.

[TheProfessor]

I wish no one would have to deal with this but I have to say I'm encouraged that Michael affected areas are not likely to be impacted much, if at all by Delta if the current trends continue...

Hopefully. I'm not saying you did, but I personally wouldn't slam the door on Panama City. While the current cone runs to Walton?Bay County on its eastern extreme, cone of uncertainty could have an eastern periphery another 100-150 miles east (or west) in the next 3-4 days. Models are pretty tightly clustered, but we all know the later in the season it gets, the more likely Gulf systems would be on the easterly side of a potential threat area (this is NOT 100% ). Just the same, there looks to be a push from the east in the Atlantic almost guaranteeing that there's some point along the Panhandle that would be too far east for it to get to. Look at Water Vapor:

Water Vapor
https://cdn.star.nesdis.noaa.gov//GOES1 ... 00x540.gif


Now run (press the play button) the GFS @ 500mb. This is easy to match up with the Water Vapor as you can see the ridging across Florida from the W Atlantic not relenting. This ridging (looks like a mid-upper level finger ridge) is clearly the feature that will direct Delta NW for a while before rounding the western periphery. BUT, down the line, the GFS has sort of backed off on the approaching long wave that was set to follow Delta by a couple of days. Now a small buckle (a really shortwave) picks it up and directs it out. The upper trough/longwave now lifts up and out after Delta does, so now there really isn't a large scale continental trough that can push it up farther east more quickly.

GFS @ 500mb
https://www.tropicaltidbits.com/analysi ... 00506&fh=6

If things stay as they are, we can narrow the expected landfall area almost to Morgan City to Navarre Beach and should be able to further hone it in as the week goes on. But again for now, there's no way Panama City should be considered out of the woods IMHO.

It's also important to note that you don't need to be inside the cone to have significant impacts, if the storm comes further east and you're on the east side of it, you're likely to be impacted in some fashion, even if you're not in the cone.

[GCANE]

Latest AMSU thermal-profile analysis shows a classic warm-core and cold-pool has developed.
Appears to have developed from a very deep cold-pool earlier.
Need to watch if the deep cold-pool pops back up.
If so, could be a monster that'll stop at nothing.

[Fancy1001]

Delta is reminding me a lot of 2002 Lili. Fast moving storm that reached its peak in the central gulf before weakening prior to landfall. The increased organization were seeing today already is pretty concerning.

Chances growing this becomes strongest storm of the season

CATEGORY 5 DELTA.

[GCANE]

A new hot tower zipping across east to west.
Should take the edge off the PVS.
Once the PVS goes, the lid comes off and this will likely RI.

[p1nheadlarry]

Looking at CIMSS, the PV Streamer appears to have gotten over the CoC.
These things can be very deceptive.
What appears to be a warm-core feature may in fact be the PVS.
It would put a lid on getting the vorts stacked.
A lot of convection firing around this though.
Usually takes about 12 hrs or so for it to shake out.
Once the PVS goes, that trof to the east would likely setup a good poleward outflow channel.

Might be a little over my head, but aren't upper level +PV anomalies cold? Wind shear from PVS is produced by vertical gradient where winds increase with height which in thermal wind balance means cold.