Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
Reged:
Posts: 2565
Loc: Melbourne, FL
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Area of Interest - Invest 91L
Tue Aug 12 2003 07:15 PM
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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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