ATL: HERMINE - Post-Tropical - Discussion

[slamdaddy]

and the drier air is pushing west to east in the gomex...just look...http://www.ssd.noaa.gov/goes/east/carb/flash-wv.html

[SoupBone]

Again as we have seen many many many times before shear can aide development during genesis and not to be forgotten. .

Do we have a deep understanding of why it can both help and hinder a system?

Largely, yes.

First off, mid or upper tropospheric wind shear can be divergent, convergent and neutral.

Divergent upper level wind/shear leads to upward vertical motion, which can aid a storms outflow/venitlation, provided the upper trough/low inducing the shear is properly placed, and eventually backs away from the system in due course.

Convergent winds/shear lead to downward vertical motion, which does the opposite. Obviously neutral shear is neither convergent nor divergent.

The extent of how detrimental shear is depends on a myriad of factors such as:

1. Magnitude (strength),
2. Level, and depth (where in the mid/upper troposphere it is and how deep of a layer it is), and
3. Whether or not it is accompanied by dry air within the shear layer.

Published studies (I think Alyono may have done some research toward this end, he can correct me if he has not) have shown that shear coupled with dry air is extremely detrimental to a TC.

Thanks for that explanation. I'll be researching this topic more, as I find it fascinating.

[HurriGuy]

 https://twitter.com/EricBlake12/status/769749388428136448

[Aric Dunn]

decided to take a comparison with the current motion of the upper low causing the shear. gfs has it staying in slight wsw motion till late tomorrow. as of right now its already due west and will soon start interacting with the upper low in the gulf. I suspect that it will begin its northerly retreat much sooner than tomorrow afternoon in which case shear may start relaxing more. 00z runs of both gfs and hwrf are nearly identical to their 12 and 18z runs euro will likely follow suit. given the high likelihood of already having a closed circ and the progression of the surrounding environment we may see a much more organized system tomorrow closer in line with the hwrf.

[SeGaBob]

40-60

[SoupBone]

decided to take a comparison with the current motion of the upper low causing the shear. gfs has it staying in slight wsw motion till late tomorrow. as of right now its already due west and will soon start interacting with the upper low in the gulf. I suspect that it will begin its northerly retreat much sooner than tomorrow afternoon in which case shear may start relaxing more. 00z runs of both gfs and hwrf are nearly identical to their 12 and 18z runs euro will likely follow suit. given the high likelihood of already having a closed circ and the progression of the surrounding environment we may see a much more organized system tomorrow closer in line with the hwrf.

So you're thinking it's going to skirt the western spine of Florida?

[slamdaddy]

decided to take a comparison with the current motion of the upper low causing the shear. gfs has it staying in slight wsw motion till late tomorrow. as of right now its already due west and will soon start interacting with the upper low in the gulf. I suspect that it will begin its northerly retreat much sooner than tomorrow afternoon in which case shear may start relaxing more. 00z runs of both gfs and hwrf are nearly identical to their 12 and 18z runs euro will likely follow suit. given the high likelihood of already having a closed circ and the progression of the surrounding environment we may see a much more organized system tomorrow closer in line with the hwrf.

Really !?!?!?

[Aric Dunn]

decided to take a comparison with the current motion of the upper low causing the shear. gfs has it staying in slight wsw motion till late tomorrow. as of right now its already due west and will soon start interacting with the upper low in the gulf. I suspect that it will begin its northerly retreat much sooner than tomorrow afternoon in which case shear may start relaxing more. 00z runs of both gfs and hwrf are nearly identical to their 12 and 18z runs euro will likely follow suit. given the high likelihood of already having a closed circ and the progression of the surrounding environment we may see a much more organized system tomorrow closer in line with the hwrf.

So you're thinking it's going to skirt the western spine of Florida?

im just talking about genesis. track right now has to many variables. also I rarely bother with the track long term.

[Aric Dunn]

center has moved and been sheared ( which was expected) away from the convection now easily seen on miami radar and RGB satellite. this process is going to keep happening. LLC after LLC developing in the convection then being sheared . this one looks a little stronger and may start more convection soon. it rotated a little north west out of the convection but has since been straight west. still has a lot of battling and if deeper convection forms again further east and se like today yest another circ may take its place.

[Aric Dunn]

Also just as I suspected the Euro has followed suit. that upper low does not look like it will dive any further south as the uppler low over the western gulf is not moving much. which should force this upper low to turn back to the nw giving the system a good shot.

[HurriGuy]

Also just as I suspected the Euro has followed suit. that upper low does not look like it will dive any further south as the uppler low over the western gulf is not moving much. which should force this upper low to turn back to the nw giving the system a good shot.

I still think it is too early to be looking 2 days past this system as bad as that sounds.

We have already been burned once looking 5 days out. I still rather wait until we get a storm and how far south and west in tracks into the Gulf

[Aric Dunn]

Also just as I suspected the Euro has followed suit. that upper low does not look like it will dive any further south as the uppler low over the western gulf is not moving much. which should force this upper low to turn back to the nw giving the system a good shot.

I still think it is too early to be looking 2 days past this system as bad as that sounds.

We have already been burned once looking 5 days out. I still rather wait until we get a storm and how far south and west in tracks into the Gulf

again only looking at model genesis. all are within 12 to 20 hours from now. thats not far out. after that im not worried about.

[Aric Dunn]

center has moved and been sheared ( which was expected) away from the convection now easily seen on miami radar and RGB satellite. this process is going to keep happening. LLC after LLC developing in the convection then being sheared . this one looks a little stronger and may start more convection soon. it rotated a little north west out of the convection but has since been straight west. still has a lot of battling and if deeper convection forms again further east and se like today yest another circ may take its place.

for those who want to see and dont have programs..

watch the last of the loop a little faster clearly the circ popped out of the convection from shear and is moving west.. but again we could easily get another circ develop if convection build east of it like it has the last couple times spitting out new circ's

http://flhurricane.com/imageanimator.php?217

[STRiZZY]

If 99L develops it should be known as 99L.. Not Hermine lol.. Tropical storm 99L l, Hurricane 99L..

[Orlando]

I am a long time reader of this forum, but just now signed up to post. It is such a pleasure to have so many brilliant weather minds to study with. You all are so good at keeping us informed with maps and information and speculation. I am grateful to everyone here.

This has been the most mystifying storm that I have seen since I have been following these kinds of events. For what it's worth, I forecast weather for myself by how much pain my arthritis gives me. Sometimes, I am more accurate than the local weather man based on my degree of pain. This go around, I do not have much pain--yet, but I anticipate having more as the storm intensifies. At any rate, I'm hoping for everyone that the damage from this storm is extremely minimal to non-existent.

Thanks, everyone, for keeping us informed!

[Airboy]

With the ASCAT and the current IR sat images I would guess it's a TD right now or will be soon.

[tropicwatch]

It appears that some sort of circulation is showing up on the radar out of Key West.

[bamajammer4eva]

This is radar estimate of echo tops along with the sat pic

[Frank2]

As the past several days, there are still several weak circulations embedded in the system as it moves slowly to the west, but the large ULL is moving along with it - hard to see anything else coming from 99L for now if at all.

If the ULL were not there that'd be another matter and perhaps the models would be right this time, but not with the present environment.

http://www.goes.noaa.gov/HURRLOOPS/huwvloop.html

[JKingTampa]

http://www.ssd.noaa.gov/PS/TROP/floater ... -long.html

Shortwave IR looking more TD-like but doubtful it'll be able to sustain it very long.