cieldumort
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Loc: Austin, Tx
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For all practical intents and purposes, Isaac appears to behave like an off-and-on TD since its Final Advisory was written.
More recently, the old, primary LLC has become prominent again, with scatterometer passes showing a well defined surface circulation, but with visible satellite confirming only somewhat organized deep convection. However, trends this afternoon suggest that with the LLC now exiting the region of higher shear that exists over the central to eastern Caribbean, convection may be getting better organized, and it is looking more possible that Isaac may end up a TD or even a tropical storm again.
Movement the past two days has been towards the west-northwest to northwest. Interests in Hispaniola, Jamaica, Cuba, Yucatan peninsula and the Lower Keys may want to monitor this system closely. Heavy rains and gusts to tropical storm force are already occurring regardless of classification.
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cieldumort
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Reged: Mon
Posts: 2114
Loc: Austin, Tx
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Timely images
(Top): SSMIS F-18 Composite microwave from 2211z today lines up well with the blowup of banding convection and lighting that looks to be collocated with Isaac's re-energized LLC (Bottom).
Isaac may be very close to if not now becoming a bona fide TD again while just east of Jamaica.
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cieldumort
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Loc: Austin, Tx
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09/17 0z models are rolling in. So far, one concerning. The rest, not so much.
HWRF - TD by 09z Tuesday. Tracks through Straits of Yucatán, clipping extreme western Cuba, as a 999mb Tropical Storm early Wednesday. Enters southern Gulf Wednesday afternoon and begins deepening at a healthy clip. 979mb Cat 2 hurricane by 06Z Friday in the central Gulf. 975mb Cat 3 Major by 18Z Friday south of Louisiana.
HMON - Basically analyzes Invest Isaac as a TD already, and thus initializes the run as such. Devolves into a wave that appears to track into the Gulf though end of run.
GFS - 0z begins as a sloppy open wave. Eventually crosses into Mexico by 0z Sat without developing.
FV3 - 0z begins as a sloppy mostly open wave. Washes out in the Bay of Campeche by 06Z Friday.
ICON - 0z begins with mostly closed 1008mb Low centered just east of Jamaica. Opens/closes/opens/closes and stays weak across Straits of Yucatán, finally stalling out and closing back off near Corpus Christi, TX by 09z Sunday. Washes out over deep south Tx as a likely heavy rain maker.
CMC - 0z begins as a sloppy open wave, after having analyzed it as closed off during the day Sunday. Closes back off by 18Z Monday with a 1010mb Low. Opens and closes again. Closed weak Low in southern Gulf by 18Z Wednesday. Remains mostly wavy with vort max tracking into SE TX by 18Z Friday.
ECMWF - 0z begins as a weak closed Low centered just southeast of Jamaica. Opens back up and splits in two by 0z Thursday. By 0z Friday the southern extent of trof crosses Yucatan and into BoC, with the northern branch tracking across Keys. Breezy showers likely for each location, but no tropical cyclone.
ECMWF Ensemble-implied probability of TCG within 72 hours (from 09/16/12z run): 25%
As a side note, after looking good throughout the day Sunday and into early night, Invest Isaac looks to be getting hit with some northerly shear, having not tracked west enough yesterday to avoid it, and is on a dramatic weakening trend at this time.
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cieldumort
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Reged: Mon
Posts: 2114
Loc: Austin, Tx
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Conditions for Isaac's development in the SW ATL at the start of this new week are less favorable than what was being advertised a week ago. Additionally, the now former tropical cyclone is in even worse shape than what most models were expecting just a few days ago. Really, the only model left that redevelops Isaac is the HWRF, but this is not a reliable genesis model, and has been too bullish on Isaac all along. has unsurprisingly lowered the odds of TC formation down to just 10%. ensemble implied probably of formation is even less.
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