ATL: ISAIAS - Post-Tropical - Discussion

[ouragans]

Once again, no data from best track at 6z

[STRiZZY]

A below the belt blow?

GFS is hinting at the possibility that if this doesn't develop in the Bahamas or remains weak, the wave will continue west, consolidate in the W Carib and move into the GOM with possible development.

At this point, its a TX / LA landfall.

Looks like one way or the other, something is going to happen.

https://i.imgur.com/Pi5TtWn.png

https://i.imgur.com/LPzf8M4.png

The GFS takes 92l through the Bahamas and runs it up the FLA/GA/SC coast. I think the system hitting LA at 300hr isn't a part of 92l.

https://www.tropicaltidbits.com/analysis/models/gfs/2020072800/gfs_z850_vort_watl_35.png
You can see what becomes of 92l off the FL space coast and the system that ends up hitting LA is NW of Jamaica, S of Cuba on this vorticity map.

Its the remnant of the wave currently associated with 92L.
Follow the MSLP & PWAT forecast.
PWAT is the same as TPW. Its what you would see on CIMSS's MIMIC-TPW.

https://i.imgur.com/tmxFrf6.png

Yeah I'm not seeing how that's associated with 92l at all tbh. That energy comes from deep in SE Caribbean (just north of Venezuela) while what becomes of 92l is off the coast of FL. If I could post from Maue's site id show you the integrated vapor transport map that shows this more clearly. Either way that's something to watch for in the future.

[GCANE]

Mixed message from IR satellite as if this is closed off or not at this time.
However, good solid warm core, but very broad.

[GCANE]

The GFS takes 92l through the Bahamas and runs it up the FLA/GA/SC coast. I think the system hitting LA at 300hr isn't a part of 92l.

https://www.tropicaltidbits.com/analysis/models/gfs/2020072800/gfs_z850_vort_watl_35.png
You can see what becomes of 92l off the FL space coast and the system that ends up hitting LA is NW of Jamaica, S of Cuba on this vorticity map.

Its the remnant of the wave currently associated with 92L.
Follow the MSLP & PWAT forecast.
PWAT is the same as TPW. Its what you would see on CIMSS's MIMIC-TPW.

https://i.imgur.com/tmxFrf6.png

Yeah I'm not seeing how that's associated with 92l at all tbh. That energy comes from deep in SE Caribbean (just north of Venezuela) while what becomes of 92l is off the coast of FL. If I could post from Maue's site id show you the integrated vapor transport map that shows this more clearly. Either way that's something to watch for in the future.

They way I look at it is: what happens to the moisture, where does it go.
Its along the lines of conservation of mass.
If the LL vort deepens, it entrains more moisture and shoots it up in the atmosphere as convection.
If the vort is weak, less convection and more moisture remains in the wave.

[STRiZZY]

A lot of shear north and west of 92l.

[GCANE]

A lot of shear north and west of 92l.

http://tropic.ssec.wisc.edu/real-time/atlantic/winds/wg8shr.GIF

It's under an anticyclone and the shear gradients are whats firing the convection due to associated lift.

http://www.geosci.sfsu.edu/geosciences/ ... /print.htm

Vertical wind shear influences storm organization by enhancing the ability of a thunderstorm outflow (or cold pool) to trigger new storms. By itself, a cold pool can only trigger new cells if the upward motion at its leading edge can lift the warm air to its LFC. In a uniform environment, when the vertical wind shear is weak, no one portion of the gust front especially favors new cell growth. Of course, since the atmosphere is generally NOT uniform, there are usually areas along the outflow boundary where lifted warmer air may more easily reach the LFC.

As vertical wind shear increases, the interaction between the shear and the cold pool becomes an additional factor that can enhance the lifting on a preferred storm flank. This enhanced lifting occurs even in a relatively uniform environment. We can describe this shear/cold pool interaction through the concept of horizontal vorticity.

[STRiZZY]

A lot of shear north and west of 92l.

http://tropic.ssec.wisc.edu/real-time/atlantic/winds/wg8shr.GIF

It's under an anticyclone and the shear gradients are whats firing the convection due to associated lift.

http://www.geosci.sfsu.edu/geosciences/ ... /print.htm

Vertical wind shear influences storm organization by enhancing the ability of a thunderstorm outflow (or cold pool) to trigger new storms. By itself, a cold pool can only trigger new cells if the upward motion at its leading edge can lift the warm air to its LFC. In a uniform environment, when the vertical wind shear is weak, no one portion of the gust front especially favors new cell growth. Of course, since the atmosphere is generally NOT uniform, there are usually areas along the outflow boundary where lifted warmer air may more easily reach the LFC.

As vertical wind shear increases, the interaction between the shear and the cold pool becomes an additional factor that can enhance the lifting on a preferred storm flank. This enhanced lifting occurs even in a relatively uniform environment. We can describe this shear/cold pool interaction through the concept of horizontal vorticity.

Thanks for that link.

[GCANE]

A lot of shear north and west of 92l.

http://tropic.ssec.wisc.edu/real-time/atlantic/winds/wg8shr.GIF

It's under an anticyclone and the shear gradients are whats firing the convection due to associated lift.

http://www.geosci.sfsu.edu/geosciences/ ... /print.htm

Vertical wind shear influences storm organization by enhancing the ability of a thunderstorm outflow (or cold pool) to trigger new storms. By itself, a cold pool can only trigger new cells if the upward motion at its leading edge can lift the warm air to its LFC. In a uniform environment, when the vertical wind shear is weak, no one portion of the gust front especially favors new cell growth. Of course, since the atmosphere is generally NOT uniform, there are usually areas along the outflow boundary where lifted warmer air may more easily reach the LFC.

As vertical wind shear increases, the interaction between the shear and the cold pool becomes an additional factor that can enhance the lifting on a preferred storm flank. This enhanced lifting occurs even in a relatively uniform environment. We can describe this shear/cold pool interaction through the concept of horizontal vorticity.

Thanks for that link.

Your welcome

[GCANE]

CIRA Snow / Cloud showing a very well UL Outflow / Divergence

[supercane4867]

I doubt this system, once developed, will fall apart as quickly as some global models suggested. While a large circulation like this takes more time to consolidate, it is also more resilient to wind shear and land interaction. Dry air is not going to kill it off but may get entangled into the core which would limit intensification, and that's about it.

[Dean4Storms]

I doubt this system, once developed, will fall apart as quickly as some global models suggested. While a large circulation like this takes more time to consolidate, it is also more resilient to wind shear and land interaction. Dry air is not going to kill it off but may get entangled into the core which would limit intensification, and that's about it.

Depends on how strong the wind shear and if it’s surface low is tangling with the Greater Antilles and those mountains as well. If that is happening at the same time it’s doomed.

[SouthFLTropics]

I doubt this system, once developed, will fall apart as quickly as some global models suggested. While a large circulation like this takes more time to consolidate, it is also more resilient to wind shear and land interaction. Dry air is not going to kill it off but may get entangled into the core which would limit intensification, and that's about it.

Depends on how strong the wind shear and if it’s surface low is tangling with the Greater Antilles and those mountains as well. If that is happening at the same time it’s doomed.

I think there is a good possibility that the islands may help, not hurt, 92L. We have seen many times before where the frictional effects of land help a loosely organized system consolidate. I think that is what 92L needs more than anything right now is some help bringing everything together. PR and Hispaniola might be exactly what the doctor ordered.


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[Aric Dunn]

Morning visible is pointing towards the western convention with the southerly flow curving to the NW.

[Aric Dunn]

Well at least we know moisture wont be a problem.. lol

And honestly, it does not matter where the LLC finally consolidates..

it wont miss the islands.

[Weatherboy1]

Still looking in track to be designated this morning, as I expected yesterday afternoon. Only missing ingredient was increased convection and clearly over the last 12 hours, we’ve gotten that. May not be a strong consolidated center but think we see that soon and it’s a TD at 11 am, again IMO

[USTropics]

Another sign the SW lobe is becoming the focal point, watch how the vorticity signature in the mid-upper levels has propagated from the NE to the SW over the past 18 hours:

mid-level


upper-level

[toad strangler]

That's a pretty decent signature up at 500mb

[Do_For_Love]

The western lobe looks strong, the rest of it not as much. Maybe the elongation will keep it from being able to consolidate? Or maybe it will be a very lopsided storm? Idk.

[Aric Dunn]

Here is the general Idea right now... and yes my mouse drawing skills still suck..

The eastern lobe is in a losing battle both by size and momentum.

Eventually the eastern lobe will get strung out as the western low deepens throughout the day.

There is definitely curved inflow going into the western lobe which there is likely a LLC.

But the eastern lobe has no curved inflow... just into the convection then back out.

[Shell Mound]

If the southwestern lobe manages to become dominant, then the weaker, northeastern lobe, combined with the TUTT, could drag 92L/Isaias a bit farther north as it nears the northeastern Caribbean, especially if current trends continue and the SW lobe manages to consolidate faster within the next day or so. As angular momentum transfers to the southwestern lobe, the weakening, northeastern lobe rotates counterclockwise around the dominant lobe, while the circulation (wave axis) begins to align at the middle and upper levels. As the deepening system interacts with the TUTT near the islands, the dominant, southern lobe will still be drawn northward, then begin to push the TUTT away by days three through five, given an early start on development within the next twenty-four to thirty-six hours. So 92L/Isaias could still manage to avoid the larger islands of the Greater Antilles and instead interact with Puerto Rico and the Leewards at most (prior to the Bahamas, of course). Given current trends toward a slower, deeper shortwave trough over the southern Plains, a stronger 92L/Isaias could reinforce the stronger ridging to its north via diabetic outflow, which also serves to weaken the nearby TUTT, primarily by days three through five. This would imply a greater threat to FL/GA and perhaps the extreme eastern Gulf of Mexico. Current trends on satellite definitely suggest imminent development, with widespread deep convection persisting through the early diurnal minimum. For once the GFS-Parallel and the HWRF may be onto something.