Mon Sep 08 2003 10:29 PM
Re: Westward turn?

wobble maybe. if it's doing it for four hours or so you can start considering it a turn. think maybe i'm starting to see how the upper pattern ahead of isabel is evolving. upper trough ahead is stretching and disconnecting, with the northeastern of the three upper centers nudging east, the middle one pinwheeling westward around the large one to the south (which is heading west itself). as the trough to the west breaks down it may become an outflow jet, with the ridging currently north of the trough building across the hurricane. meanwhile the upper trough behind isabel continues to dig in, in tandem with its advance. basically there will be two ventilating upper lows on either side, with a ridge built across to the north.. if i'm reading the wv evolution right. models are trending toward the remnant disturbed weather with henri to shear away, though some persist the disturbed weather. the upper system ahead of isabel is tracked wnw to near the bahamas, then gfs degenerates it to a trough and sends it out as shortwave over the east grabs it.. around the weekend.. while some of the upper energy associated with the shortwave splits and digs into the central u.s. the result of this is the subtropical ridge north of isabel advancing into the southeastern united states in about a week... with the storm advancing underneath.
for this to verify it will take a lot of things happening together.. models will evolve closer to the truth over time.. all it takes is the model tendencies to weaken upper troughs too quickly, or time shortwaves wrong or get the amplification of ridges/troughs incorrect down the road.. but if things verify even close to the current trends we could have a very bad situation on our hands next week.
other things to watch..
1) td 14. if the convection doesnt regenerate in the next 12hrs or so, call it dead. watch to see if it goes up ahead of the upper trough ahead of it, or if it keeps low and nudges westward as weak system.
2) wave near 70w. this is a weak wave, but it may move into a favorable environment by late in the week west of jamaica.
3) henri's tail. trough tails back from henri's low towards south florida. upper ridging that henri originally developed under is the currently the western piece of the subtropical ridge.. trough under ridge.. you get the picture. low to the north would have to weaken for it to become a significant feature.
4) pacific development. watch the itcz disturbance near 90w, a developing eastpac system would alter the nearby upper air features, propagating upstream into the atlantic. it might also precipitate more atlantic development
5) fabian's wake. isabel is north of it, and shouldnt cross it (if it follows the nhc path) for about 3 days. still, it crossed fabians early path a few hours ago, and the convective tops have weakened some (may be an effect of dry air entrainment, or the start of eyewall contraction cycles).
there, thats enormous and probably pseudo-science as i've possibly analyzed past the extent of what i know about synoptic weather.. but just maybe i've got some of the ideas right.
HF 0230z09september

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