99L a significant threat to the Bahamas; Could become huge east coast storm

By: Levi32 , 9:21 PM GMT on October 21, 2012

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12. WunderAlertBot (Admin)
4:17 PM GMT on October 23, 2012
Levi32 has created a new entry.
11. beell
11:12 PM GMT on October 22, 2012
NHC weighs in on the mechanisim for lifting Sandy out of the Caribbean. Previous runs of the GFS have not resolved this trough very well in the mid levels but has done a decent and consistent job with the amplifying (and shear producing) upper level trough. I suppose as Sandy strengthens, it will provide enough of a mid level weakness. I attributed it to the mid level ridge lifting north. We'll see, as you say!


TROPICAL DEPRESSION EIGHTEEN DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012
1100 AM EDT MON OCT 22 2012

A DEVELOPING MID- TO UPPER-LEVEL TROUGH OVER CUBA
SHOULD PULL THE DEPRESSION NORTH-NORTHEASTWARD TOWARD JAMAICA AND
EASTERN CUBA.

TROPICAL STORM SANDY DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012
500 PM EDT MON OCT 22 2012

GLOBAL MODELS PREDICT THAT THE
MID-TROPOSPHERIC RIDGE TO THE NORTH OF SANDY WILL GRADUALLY WEAKEN
WITHIN THE NEXT DAY OR SO...WHICH SHOULD ALLOW THE TROPICAL CYCLONE
TO BEGIN MOVING NORTH TO NORTH-NORTHEASTWARD SOON.
Member Since: September 11, 2007 Posts: 141 Comments: 16271
10. watercayman
8:31 PM GMT on October 22, 2012
Thanks Levi - welcome back.
Member Since: September 13, 2007 Posts: 0 Comments: 82
9. LakeWorthFinn
3:32 PM GMT on October 22, 2012
Thanks :)
Member Since: October 6, 2005 Posts: 67 Comments: 7281
8. originalLT
12:52 PM GMT on October 22, 2012
Thanks for taking time to post again, I was concerned that you were all right. Good to hear that you were "just" busy! Thanks again ,hope you will post more as this storm keeps developing.
Member Since: January 31, 2009 Posts: 0 Comments: 7450
7. beell
10:38 PM GMT on October 21, 2012
Quoting Levi32:


Well since heights are high over northern Mexico during the period, 99L can't really go west, so that option is shut off. I think it gets drawn north due to a kind of self-propagating mechanism. Since there is a strong pressure gradient over the Bahamas during the next 3 days, the convergence there will tend to lower pressures north of 99L's center, and since there is no dominant steering current, it ends up being drawn northward in the direction of falling pressures. We seem to see this kind of situation a lot with late-season Caribbean storms.


That might do it. I have the notion (emphasis on "notion", lol) that any LLC will make a cyclonic loop around the larger low pressure area covering most of the Caribbean-beginning with a SW turn. Your idea of a "self-propagating mechanism" may be more likely.

Thanks.
Member Since: September 11, 2007 Posts: 141 Comments: 16271
6. SunnyDaysFla
10:10 PM GMT on October 21, 2012
Thank you Levi. Great to see a "tidbit" again.
Member Since: September 19, 2008 Posts: 0 Comments: 522
5. Dakster
10:05 PM GMT on October 21, 2012
thanks Levi!

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4. Levi32
10:04 PM GMT on October 21, 2012
Quoting beell:
Great work, Levi. Thanks.
What, in your opinion, pulls 99L far enough N to allow the 500mb trough to grab/influence track? Models begin bringing 99L north well in advance of the trough.


Well since heights are high over northern Mexico during the period, 99L can't really go west, so that option is shut off. I think it gets drawn north due to a kind of self-propagating mechanism. Since there is a strong pressure gradient over the Bahamas during the next 3 days, the convergence there will tend to lower pressures north of 99L's center, and since there is no dominant steering current, it ends up being drawn northward in the direction of falling pressures. We seem to see this kind of situation a lot with late-season Caribbean storms.
Member Since: November 24, 2005 Posts: 635 Comments: 26566
3. Slamguitar
9:48 PM GMT on October 21, 2012
Great post Levi! Very informative.
Member Since: July 2, 2011 Posts: 0 Comments: 1183
2. beell
9:39 PM GMT on October 21, 2012
Great work, Levi. Thanks.
What, in your opinion, pulls 99L far enough N to allow the 500mb trough to grab/influence track? Models begin bringing 99L north well in advance of the trough.
Member Since: September 11, 2007 Posts: 141 Comments: 16271
1. Grothar
9:31 PM GMT on October 21, 2012
Good one. Very complete. Let's see what happens. We are looking for wet and windy week-end down here.
Member Since: July 17, 2009 Posts: 69 Comments: 25484

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Levi Cowan has been tracking tropical systems since 2002, and is currently working on his bachelor's degree in physics at UAF.

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