...WEDNESDAY DECEMBER 5 2012...9:00 PM EDT...
Non-tropical remnant surface low of former subtropical disturbance Invest 91-L...and associated upper vortex...has entered the high-latitudes northwest of the Azores as remarked in paragraph P3 of full discussion #169.
Eastern divergence of cut-off upper troughing from from the eastern Caribbean...extending east-northeast to the central Atlantic...continues to support open Atlantic surface troughing and thunderstorms southwest of ex-91L as remarked in paragraph P5 in full discussion #169. The surface low along the surface troughing has intensified to 1006 mb while moving quickly northeast. Even though westerly shear ahead of the cut-off upper troughing has reduced due to its amplification...and even though the 1006 mb surface low is over sub-20 deg C water capable of supporting a subtropical disturbance...the surface low is moving quickly northeast into even cooler waters and is becoming non-tropical while merging with the front extending southwest from ex-91L. Therefore subtropical development from this system is not anticipated.
In the northern Gulf of Mexico...a well-organized comma shaped area of scattered thunderstorms has developed in assocation with eastern divergence of a highly-amplified cut-off upper trough and surface frontal depression. The surface frontal depression is along the cold front extending from the non-tropical cyclone mentioned in paragraph P1 of discussion #169...while the cut-off upper trough is a southern fracture of the central United States upper trough mentioned in that same paragraph. The south half of the disturbance is over waters in the 20s of deg C...the surface frontal depression is currently under low shear beneath the highly-amplified cut-off upper trough...and a comparison of surface air temps from Texas to Florida show little air mass contrasts across the surface fronal depression. While these are principles that could convert a surface frontal depression to a more subtropical feature...westerly vertical shear is expected to increase quickly as the cut-off upper trough de-amplifies thanks to warm air advection ahead of the next frontal system moving into the western United States. Therefore no subtropical development is expected here either.
With no indications of subtropical or tropical development in the near-term...I have stopped full birdseye chart discussions for the Atlantic hurricane season. Full birdseye chart discussions will resume on this blog when the Atlantic hurricane season re-starts in June 2013. Special updates and or full birdseye discussions could resume before that time if once again any out-of-season tropical or subtropical activity occurs in the Atlantic basin.
Sometime early in 2013...I will be releasing post-storm reports for the 2012 Atlantic Hurricane Season which will include an evaluation of how my storm forecasts (issued on this blog) compared with that of the official forecasts from the National Hurricane Center.