BigA wrote:Taking a closer look, it makes sense that the LLC is dissipating, while the overall large-scale circulation remains. Looking at the 850 vorticity map, the vorticity over the circulation hasn't weakened. However, that is satellite-derived and likely unable to pick out small-scale changes such as the weakening of the small LLC. Once (if?) the upper-level low weakens, I like 92's chances as long as it moves more west than north in the short run.
Very important point there about the fact that those vorticity charts are satellite derived and can change very quickly. This scenario is a perfect example. IMO the ULL is just about done. From the water vapor loops it looks like it droped slowly southwestward today and the last of it finally got elongated and dissipated just in the last few frames. One of the last things it contributed to this whole scenario was that the southwest to south winds on the southern side of it helped shift the vorticity in the system more northward. I would think the vorticity charts over the next few hours will start showing this northward shift in the vort max from 850mb to 500mb.
There will be a lot of post mortems done on this later, especially if it makes TC. I also watched this all day long and think that the ULL and the MLC that was developing with this system simply merged or are almost merged. But the ULL had started to elongate and weaken as this happened. From the atmospheric physics involved here, that ULL couldn't get any further south than it got this afternoon. Having no more room to move south it got stretched by the squeeze of the northerly winds to its west and the strong southerly winds to the east around the subtropical high. But at the same time the building convection and residual mid-level vorticity from the original disturbance were forming an MLC and the mid-level downward extension of the ULL just merged with it. No matter what really happened there, it appears to me that there is now a discernible MLC and no more ULL. That was forecast by the models anyway.
