Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
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Loc: Melbourne, FL
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Worth noting that this system evolved from a cutoff upper level low that had its origins at 40N 50W many days ago. It moved around the back of the Atlantic ridge (actually through a weakness in the ridge) and at 18Z this Tuesday afternoon was centered near 26.0N 68.7W so its already had a long journey. On Sunday at 12Z it was at 26.8N 57.2W so movement has been just south of due west for the last two days. It has some good convection with it this afternoon and I'm sure that this is the 'second center' that some of you have observed, however, this is a mid to upper level center.
A few days ago the upper level low generated a reflection at the surface and that low level center has maintained itself rather well. At 12/18Z, the low level center was located at 23.2N 71.8W and it was moving to the west at about 18mph. Although the circulation itself is healthy, there is only minimal and sporadic convection with the low level center. On Sunday at 12Z this center was located at 24.0N 58.4W, so overall movement has also been just south of due west.
Will it intensify and where will it go? This year (and probably like most any other) those are tough questions  Most of the models slowly intensify the system and send it toward northeast Mexico (south of Brownsville). Well...maybe, on both questions. There are two primary players in the eventual future of 91L...and I don't believe that the Atlantic ridge is one of them. An upper level low, currently southeast of Jamaica, was forecast to move to the west southwest toward Nicaragua/Honduras in the model runs of a couple of days ago, but the low is just about stationary with maybe a slow westward drift. Invest 91L is moving westward at a steady clip as influenced by the northern circulation around the upper level low. The upper level low itself has intensified and expanded westward but the center has not moved westward - at least not at the same speed.
High pressure aloft, from Kansas to south Texas, is diving southward into northern Mexico. The east coast trough extends from southern Mexico to the Carolinas but it has not moved all that much. It has oriented a little more southwest to northeast - probably associated more with the intensification/expansion of the upper low near Jamaica rather than the anticipated retrogression of the east coast trough. The Texas high seems to have blocked the westward expansion of the Atlantic ridge - at least for the moment. Net result of all this is that some slow intensification of 91L is certainly possible and that a near-term westward track seems likely - but I'm not as convinced about the long-term projections for this system. As always, counterpoints are welcomed.
Cheers,
ED
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HanKFranK
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Loc: Graniteville, SC
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my obs: think the northern part of the system is going to become dominant. there is an elongation to it, and the upper extent of the low/trough has an anticyclone apparent overhead. also the low level easterlies are weaker at that subtly northern latitude.. suspect this area where convection is present and regenerating is where a real SFC center will evolve.
as far as future track goes.. i'll just set some landmarks and see how they turn out.
tomorrow this time, close to the coast in SE florida, tropical storm. onshore overnight.
late thursday, tropical storm, west of naples, south of the panhandle.
from there i think it will head more or less due west, reaching the western gulf coast on sat night/sun morning.
going to once over the models and see what support for these ideas is there. sort of unusual to start making predictions before checking resources.. but that's my gut talking.
anyhow, if ed's implying a recurvature in the gulf i'm skeptical of the idea. mostly because this trough has to get out of here some time soon or i'll go nuts.
by the way, see the convection in west africa? no, not the level stuff, i'm talking over mauritania and the western sahara. what in the world? maybe our SAL layer or super-dry air mass is about to change.
HF 2326z12august
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Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
Reged:
Posts: 2565
Loc: Melbourne, FL
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I agree regarding the northern system becoming dominant. Late this afternoon the swirl at 23N really got elongated east-west, probably due to some strong easterlies, and tonight the system is difficult to identify. The mid-level center has weakened some, but it is still well organized and may indeed get strong enough to generate a new low-level circulation.
I wasn't thinking about recurvature though, I was actually thinking about more of a movement to the southwest from about mid-Gulf westward. But that was with the southern center which may no longer be a player. I haven't checked out Africa in awhile - guess I should.
Cheers,
ED
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Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
Reged:
Posts: 2565
Loc: Melbourne, FL
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Tough to find a center on IR, but at 14/03Z I placed it at 26.4N 78.2W (at 13/18Z it was roughly at 26.0N 75.8W). This track would put the center near Lake Worth between 4 and 5am Thursday morning.
ED
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