typhoon_tip
(Meteorologist)
Sat Sep 09 2006 11:17 AM
Florence nearing Hurricane Status

There are enough subjective satellite observations to suggest Florence is a hurricane, however, TPC has found that the vertical structure is tiltling NW and that they could not find an eye.

...Structural integrity is a factor in the analysis process.

This tilting makes some sense when considering the larger synoptic scale reasoning. There is a deep layer ridge with an axis near 55W/35N and this is imparting a SE to NW pointing vector in the vicinity of Flo'. The sfc to ~H85 flow may have more westerly component, while the ~ H85-H7 field may be more SE... This would be more of a velocity shear as opposed to a directional shear, so may not show up very readily by satellite observations, but would certainly manifest its self as stress to the vertical structure of the cyclone. And, it is probably a nice homage to the direction of continued motion during the nearer term. If this tilting TPC is suggested really exists, it is also probable that the llv aspect (coupled environment) is having to occasional step N up underneath the core of most intense upward vertical motion. This subtle physically caused correction may be disrupting a more explosive intensity curve.

There has been some question as to the significance of the re-positioning S and also, some additional westerly component observed during the overnights.

My suggestion is this will mean very little to the track guidance, but perhaps shifting it a little to the W as Flo' begins whatever form of the parabolic motion into high latitudes she ultimately takes..

Bermuda is still under the gun. The stakes are high... The 00z and 06z operational GFS suggest now that Flo's re-curvature may not be a smooth acceleration into higher latitudes. The faster motion would be a better case scenario when having to also except a Bermuda strike, because a faster duration would of course limit the exposure to high winds/seas. However, said GFS solutions offer some deceleration option near Bermuda's lat/lon. That is at least intuitively acceptable because there is a mulit-day, multi-guidance unanimous solution for a large anticyclone to press seawards from the middle latitudes of the N/A continent. That would tend to argue for some form of lower tropospheric block or at least exertion against an out-and-out polarward motion. Not a done deal by any means; something to keep an eye on.

Just an early heads up on "07L"... The name has apparently been changed to 93L with a NESDIS T-number of 1.0. That Dvorak classification has held since last evening and currently looking out there on satellite, there is no question that a tenacious little entity does not want to give up the fight against the tyrrany of NNW shear in the area. I am hoping to do some model analysis on the deep layer environmental expectations for that, during the day. But, Bermuda's threat is more important. Perhaps with 93L we will get some tropical model output off the 12z runs.

John



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