I have not seen much this day to suade my thinking away from a system destined to less than pure tropical form in the longer run...
Currently, a 1005mb low is being depicted:
http://www.ssd.noaa.gov/goes/flt/t2/loop-vis.html ...then, click on "NWS Fronts" checkbox.
This loop clearly demonstrates, particularly in the last several frames, that a cyclonic motion in the cloud parsels has evolved during the late morning and early afternoons; my best "guesstimate" would place that axis of rotation somewhat NNE of the NWS Front product's low position. (I am aware that others may have other sources).
It is possible that a depression is getting going at this time. If you click on the "HDW-high" checkbox, the upper level winds directly over the NWS Front low position are 5 to 10 kts in a weakly diffluent field. There is a much more obvious diffluence axis along 83W by 20N, but the current potential spin up does not appear to be physically connected to that feature. What may not be readily observed by the untrained eye is that there is a different form of diffluence in the region near 21.5N by 86W.
First, if you look up along 86W by 22.5N, there are numerous 40 to 55kt winds entering the Gulf from the south. Now, if you look back along where the axis of rotation is, note those upper level winds are much, much lighter. The intermediate region between these lighter winds, and that of the stronger winds just to the north, is commonly referred to as an "exit jet region". This causes a lift assist, or a fluid dynamic process that helps to excite upward vertical motion. When that upward vertical motion persists for a certain length of time, the converging winds nearer to the surface will finally have integrated enough coriolis momentum to begin responding to that virtual force. Rotation ensues...
Not intending to delve too deeply into speculation here but it is quite plausible in my mind that the current cyclonic gyration amid the convergence at the surface is at least in part a response to this transient (temporary) jet configuration existing just to the north. The upward vertical motion that responded to this form of diffluence, triggered better surface convergence.
Be that as it may, and may indeed help a depression to be formed in that region, the governing synoptic points covered in the last thread by Clark, HF and myself have not changed. The pattern on whole over the eastern U.S. and adjacent Gulf is going through a period of amplification, featuring trough tendencies at lower latitudes. That is why a band of stronger mid and upper level westerlies can be noted extending SW to NE through just to the north of the Yuc. Penn. Any evolution or changing in the regional jet configurations is slated to do so quite slowly over the next day and a half. That means that spatially, this system has very limited wiggle room in the nearer terms. A drift toward the north precariously involves it in these westerlies and that is in fact bodily what the majority of the guidance is suggesting. Once that motion ensues, I do not see this developing very well because it will only mean shear ever increasing.
Again, it is possible also that if the system were to assume a NE motion along the wind vectors at greater speeds, this relative motion would reduce the impactive wind velocities, thus reduction in shear. That may allow some intensification to take place, but still not ideally so... That result would more likely be a tilted system, where the typical structure is heavy rain/thunder extending northeast along a quasi-warm frontal trough, with a partially exposed surface circulation on the southwestern edge of the deeper convection. That is quite common in these situations quite frankly.
The other aspect is that with stronger and coherent jet structures involved, that would also force baroclinic dynamics in the maelstrom. The cyclone phase state will transition to baroclinic as it cross Florida and gets embedded in the larger scale circulation of the eastern U.S. trough.
It is important to keep in mind that these phase state changes take place along a spectrum. As this system crosses Florida, the ECM is in fact developing a fairly potent and compact coastal system up along and just off the Mid Atlantic in the 00z run. If this were to verify, there will be a plume of latent heat drawn up out of the tropics; even though the system has taken on baroclinic characteristics along its route this may be detected by interesting satellite presentations, as well as ground truth. ...The 12z ECM is due out any time now... This models has been the most consistent with the track guidance and ultimately also is about down the middle of the envelope. It thus seems reasonable to assess it as the most likely course, so the new run will be interesting.
[EDIT] -- I forgot to mention... This system will likely be moving right along by the time its most likely impact is felt, over Florida. For this, I do not believe "excessive" rains will take place. However, it will certainly rain quite hard for few hours. Flash flooding is always a concern, even in very dry antecedent conditions that is true; a ton of rain in a short period of time might simply exceed absorption rates. Overall, however, this may prove more beneficial than destructive as far as the flood concern goes...
John
Edited by typhoon_tip (Thu May 31 2007 02:20 PM)
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