ATL: SALLY - Post-Tropical - Discussion

[Hypercane_Kyle]

From the 11 AM discussion.

Northwesterly shear continues over the cyclone, but this shear is
expected to decrease later today and tonight as Sally moves beneath
a narrow upper-level ridge axis. This more conducive upper-level
pattern is expected to allow the tropical storm to strengthen while
it moves over the north-central Gulf of Mexico tonight and Monday.
Most of the intensity guidance calls for Sally to become a hurricane
in about 24 hours and so does the official forecast. Additional
strengthening is expected after that time and Sally could be
slightly stronger at landfall than indicated below since it is
forecast to reach the coast between the 36 h forecast point and
48 h when it is inland over southeast Louisiana. The NHC intensity
forecast is close to the consensus aids through 24 hours and at or
just above the SHIPS, LGEM and HFIP corrected consensus aids at 36
and 48 hours.

[GCANE]

Another warm-core signature from the last tower.

Hi gcane, can you explain what you mean by a warm-core signature?

Think of it as a mini eye.
ON IR, you have to watch where a tower fires and how it rotates. The tower is a cold top.
When the tower dissipates, there is a small warm spot around the center of where the rotation was.
Its latent heating of the upper troposphere.
The more and rapid this happens, it creates a larger area of above ambient warm air. That is the warm core.
When new towers then fire and circulate around the warm core, that is eyewall building and then the eye forms.

[GCANE]

Miss Piggy on the way in.

[GCANE]

Pretty much on forecast track

[pcolaman]

Pretty much on forecast track

https://i.imgur.com/tZ7ls83.png

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

Looks Just a hair north of track.

[Sanibel]

Sally is a flooder...We are at flood level here on Sanibel Island with the pond over its banks and wetlands flooded...Not the worst I've seen but getting there...Haven't seen tropical storm flooding like this in over 15 years...

[tropicwatch]

Getting tropical storm force gusts near Apalachicola. Sustained TS winds approximately 20 miles south of St. George Island.

[gfsperpendicular]

Another warm-core signature from the last tower.

Hi gcane, can you explain what you mean by a warm-core signature?

Think of it as a mini eye.
ON IR, you have to watch where a tower fires and how it rotates. The tower is a cold top.
When the tower dissipates, there is a small warm spot around the center of where the rotation was.
Its latent heating of the upper troposphere.
The more and rapid this happens, it creates a larger area of above ambient warm air. That is the warm core.
When new towers then fire and circulate around the warm core, that is eyewall building and then the eye forms.

Thank you gcane (and nimbus), I can see what you are talking about.

[GCANE]

Diurnal pressures about to max out.
Will begin to fall in about 3 hours.
Will give Sally a boost.
Should see some good organization towards sunset.

[GCANE]

Hi gcane, can you explain what you mean by a warm-core signature?

Think of it as a mini eye.
ON IR, you have to watch where a tower fires and how it rotates. The tower is a cold top.
When the tower dissipates, there is a small warm spot around the center of where the rotation was.
Its latent heating of the upper troposphere.
The more and rapid this happens, it creates a larger area of above ambient warm air. That is the warm core.
When new towers then fire and circulate around the warm core, that is eyewall building and then the eye forms.

Thank you gcane (and nimbus), I can see what you are talking about.

My pleasure.

[Shell Mound]

Be careful saying things like "shear is no longer an issue". The TC is still being sheared. The TC is still very asymmetric. However, recent trends show an uptick in precipitation near the TC center. We saw a similar process for a stretch about ~6 h ago, but that reach toward symmetry failed. We will have to see if convection can successfully migrate toward the upshear regions, or if this is just another temporary blip. On radar, I can see what seems to be some mid-level precip cells still getting ripped off to the SSW, indicating the presence of persistent mid-level shear. I am skeptical we will see any rapid uptick in organization as long as this is occurring. Even if the storm intensifies, shear will still affect the system.

Today is a very important day for the future intensity of Sally. If the storm becomes aligned and more symmetric by tonight, like the 00Z HWRF showed, the potential for a stronger hurricane exists. If not, Sally will likely have a much more limited amount of time to significantly intensify before landfall.

One major negative factor is the massive AWB just south of Long Island, NY. When combined with the large-scale ULL/TUTT over the southernmost Sargasso Sea, this kind of pattern fosters convergence, sinking air, and the formation of a small but potent ULL over the Carolinas. This setup imparts persistent northwesterly shear over Sally, despite otherwise conducive conditions for RI, with large-scale flow favouring dual outflow channels to the west, east, and north, given Sally’s ideal position in the col, between two retrograding ULLs, with robust anticyclonic flow partly established over the circulation and a continental trough approaching. However, the AWB results in a sharper trough axis with greater linear forcing over portions of the Mississippi River Valley. Had the pattern been less amplified, perhaps Sally would have intensified faster at this point. The fact that the LLC is somewhat north of the NHC’s track in the short term also indicates that the system is more disorganised than some of the guidance may have anticipated, even the HWRF. Cf. Dolly (2012): a weaker system would, in this case, likely make landfall farther east than the NHC and most of the guidance officially indicates. The HMON’s eastward track would end up being closest to reality, with landfall closer to the MS/AL border than to NOLA. The faster-than-expected short-term movement may also end up favouring this outcome, if sustained.

[mpic]

Will this move inland quickly? Seeing projections from local Houston weather people of possible 25" of rainfall and that was what they said about Harvey.

[Aric Dunn]

land based convection throughout the day today over florida should help feed the north quad and push the remaining shear axis north allowing sally to wrap up.

should see begin to occur over the next several hours.

[PTPatrick]

12z Gfs shifted to east side of New Orleans metro and up the pearl river. A fairly good shift East. Just a tad late for nhc 11 am advisory. Waiting for Hwrf, cmc, and euro...but icon and gfs are now East of lake ponchartrain. This is what I have been watching for...my fam in east Jackson county will probably have to get out for a track East of the lake.

[us89]

Will this move inland quickly? Seeing projections from local Houston weather people of possible 25" of rainfall and that was what they said about Harvey.

It won't be fast, but it will at least make progress (unlike Harvey, which did not). Harvey pretty much sat over the same area in Texas for days. Sally will be moving slowly northward for about a day or so after landfall before it picks up speed and moves off to the northeast.

[robbielyn]

Yep. In the 10-15 inch location area here at the house. Have not had any rain here this month so that may help a lil bit, not much, but a little.

10-15 inches not out of the realm of possibilities. Key West Airport has recorded 9.71 inches so far from Sally....and its still raining.

and we here in hernando have nothing

[RL3AO]

Looks like the recent convective burst wasn't enough yet. Center starting to become more exposed as it leaves the convection behind.

[Dave C]

Looks like the recent convective burst wasn't enough yet. Center starting to become more exposed as it leaves the convection behind.

This is awesome to see, people really need to catch a break after the sad outcome with Laura.

[LarryWx]

Sally fortunately still doesn’t look like it is on the verge of anything approaching RI based on it still looking sheared pretty decently to the east in vis loops but of course that can still change later.

[johngaltfla]

Yep. In the 10-15 inch location area here at the house. Have not had any rain here this month so that may help a lil bit, not much, but a little.

10-15 inches not out of the realm of possibilities. Key West Airport has recorded 9.71 inches so far from Sally....and its still raining.

and we here in hernando have nothing

I'll ship you some of my floating back yard. I see what Sanibel was talking about as we've had non-stop rain since about 1 a.m.

Good luck to Louisiana, as if this is a rain even, 20+ inches would not surprise me with Sally if she slows down and spreads out as she approaches the coastline.