ATL: HERMINE - Post-Tropical - Discussion

[Aric Dunn]

No upgrade tonight folks, low isn't closed yet.

yeah, it is. Look at the ASCAT

Yeah its pretty much closed. The signs started being present many hours ago. The shear likely helped the convection .. next question how will it survive.

[SoupBone]

the circulation is closed, but it is getting BLASTED by wicked northerly shear

Early Tuesday may be the earliestwhen this could become a TD

This area of shear has been steadily growing and increasing in wind speed all day today.

[Aric Dunn]

Fresh new convection build around llc.. thats different

[slamdaddy]

Favorable windshear is marginal at best for the moment...lest it can navigate on a dime to avoid it...just look at the cimss site.

[floridasun78]

upper low now north Bahamas that will kill 99l soon untill get into gulf

[slamdaddy]

just look..http://tropic.ssec.wisc.edu/real-time/w ... oom=&time=

[NDG]

[Aric Dunn]

upper low now north Bahamas that will kill 99l soon untill get into gulf

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

[tarheelprogrammer]

ULLs seem more prevalent in recent years. Crazy how they always arrive to limit storms when they get near the US. We will take it in coastal communities though. Life savers.

[slamdaddy]

more shear is coming...no chance for development for at least 48 hours...then after that, it will probably change again...its an hour by hour change

[SeGaBob]

more shear is coming...no chance for development for at least 48 hours...then after that, it will probably change again...its an hour by hour change

NHC doesn't agree with you.

[bella_may]

I've seen a few mets within the past 30 minutes say it's building storms around the center. Might be a TD now

[AJC3]

The low or whatever it is is SSW of Abaco

You mean Andros Island

[SoupBone]

upper low now north Bahamas that will kill 99l soon untill get into gulf

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?

[SFLcane]

Yea it will find those favorable conditions just like those its been encountering in the Bahamas.

[Aric Dunn]

upper low now north Bahamas that will kill 99l soon untill get into gulf

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?

Yes, in the short term of enhancing convection to help produce a surface circ. Afterwards you dont want shear or well you know. The timing has to be within a certain period or it just will shear apart.

[HurriGuy]

Honestly judging by the location of the lower level vorticity from latest ASCAT, and seeing how well GFS initialized, sheer is not that bad around the circulation. Now on the north side of the circulation, nothing can stand a chance with the ripping sheer, but it is understandable why storms are able to fire near the llc.



It needs to get imbedded in the upper high (the lightly blue shaded area) to get some protection from the ULL to the north

[mobilebay]

Yea it will find those favorable conditions just like those its been encountering in the Bahamas.

Yea. The models have been showing " favorable conditions in a couple days" for a week now. Problem is the couple days never get here. Its either a dust thing, or a dry air thing, or an upper low causing shear thing. I surrender

[AJC3]

upper low now north Bahamas that will kill 99l soon untill get into gulf

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.

[slamdaddy]

Its the worst it has looked so far...toaster leavins...done...no deal, not yet.