cieldumort
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Posts: 2306
Loc: Austin, Tx
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-Caribbean disturbances are gaining some respect-
Sat Oct 27 2007 07:22 AM
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Among some mets, bloggers & models, that is. And probably with some pretty good reason.
SSTs for each are fully supportive of tropical cyclogenesis. It's still October, and not mid-January, after all. So, when it comes down to if either of these guys can get going, we're mostly looking at the degree of spin/pressures, convection, and shear.
Invest 90L
Shear -
Invest 90L has begun freeing itself of the clutches of its parent ULL, continues to head WSW or SW, and by most reasonable shear measures, is now under 20 knots of shear, possibly a touch less if even figuring it as net-effective shear, and is on a heading that takes it well under 15 knots of shear during the weekend.. and possibly to even nuzzle under a very supportive upper-level wind-flow pattern with less than 5 knots shear by Sunday night. For your reference: UWCIMSS
Spin/Pressures -
90L has had a fairly well-defined surface circulation for the better part of this week. Winds have been enhanced along its northern semicircle due to a bit of a tight pressure gradient, even blowing upwards of 45 knots. Winds in the southern half have been running generally under 15 knots, with perhaps a few bouts of 20 knots per buoys, ships, NWS stations and scatterometer. Therefore, 15-20 knots is likely much more representative of the true surface circulation. Pressures have been running roughly 1005-1007 mb throughout.
Convection -
Perhaps the single largest impediment to 90L from having gotten beyond "almost there" on Thursday, at which time 90L was earning T numbers of 1.5 several times, to earning the kiss of death "too weak" during the day Friday, has been its inability to wrap deep convection about itself, because of high shear. This may, and tonight is to some extent, quickly change, should it indeed enter the low shear zone mentioned above.
Untagged area of interest in the western Caribbean
This feature has come about through the interaction of a powerful cold front which took up nearly stationary over the northwest Caribbean, a tropical wave, and a small upper-level low. System has featured an obvious mid-level cyclonic flow along with several small pockets of showers and a few thunderstorms rotating about the mid-level low, for two days or so now.
Shear-
Now down to about 10-15 knots (10 per CIMSS, but increasing a little bit in the vicinity of the mid-level low and recent burst of deep convection). For the most part, shear in the western Caribbean is favorable for further development this weekend.
Spin/Pressures-
The ULL looks to have continued to weaken, the front has begun retreating north and is washing out, and the formerly mid-level low now shows a clear and fairly robust surface reflection per the most recent QuikSCAT imagery. Pressures area-wide are relatively low.
Convection-
Somewhat intermittent and scattered at first, but not lacking tonight. A small MCS may have developed in the vicinity of the surface reflection.
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