From yesterday:
Margie wrote: it seems like the short comeback I anticipated earlier is starting, and Zeta may be looking pretty good by mid-morning, but I think now that the stronger westerlies are going to arrive earlier than the forecast 24-36 hours, unless Zeta ducks a lot more to the south, and convection could be gone by early tomorrow evening.
Well there you have it; 'course it's been a no-brainer for awhile...the anticipated buildup of convection, currently being increased by the oncoming shear, and now it's on a collision course with the westerlies, again I think earlier than predicted, likely to start ripping away the convection by 8pm tonight. Zeta really did try, with the southward movement, maybe if she'd been able to get down to say 22.5N, and if only the northern jet would have curved a little earlier and allowed that trough to slide just a little more to the north, she would have squeezed past that one too. But it is not to be.
However I'm wondering if there is a chance the well-defined LLC can survive to slip just south of the trough into the area of lower shear behind it, and develop some convection then. But I suppose that is just too far beyond reasonable possibility.
I wouldn't read too much into the oscillation between sub-tropical and tropical designations. It is an indicator that the strongest winds migrate from the center to further away and back again, which, given the history of the recent spate of TC that have formed from these cutoff lows, would seem to be the norm...just a way for the TC to survive in these borderline conditions. It is interesting how this is different from a true transition to extratropical.