MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #168A (Special Update)
*******Note that forecasts and outlooks in this post are NOT the official forecast from the National Hurricane Center (NHC). They are my own detailed views on the Atlantic tropics based on current observations and latest computer model runs. As such do not make decisions based on my posts...consult news media...watches and warnings from your local weather office...and any evacuation orders issued by local governments to make the most informed and best decisions. Visit the NHC website hurricanes.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********
...FRIDAY DECEMBER 3 2021 1:23 PM EDT...
Satellite image of newly formed surface low pressure spin located southeast of Bermuda as of 1620Z:
Hovmoller Diagram (spanning 2340Z Nov 30 to 1140Z Dec 3) showing the progression of the tail end of the upper trough (circled in yellow) which has recently generated the surface low pressure southeast of Bermuda:
With its eastern divergence zone… the tail end of the upper trough associated with the current frontal cyclone over the northeastern US and southeastern Canada has generated a surface low pressure spin southeast of Bermuda as of this morning. The tail end of the upper trough is amplified enough to keep shear levels lower such that thunderstorm activity… also boosted by the eastern divergence zone of the upper trough… is located just east of the surface low pressure instead of being displaced further away.
In response to amplification of warm core upper ridging to occur in the warm sector of the next frontal cyclone to traverse the US/Canada border region in 48 to 72 hours… recent runs of the ECMWF model forecast the tail end of the upper trough southeast of Bermuda to amplify further into a cut-off upper vortex. The resulting vortex lowers shear further to allow the surface low pressure to acquire tropical characteristics in the ECMWF solution. However the GFS and other global models are not on board with this solution at present. Even if the ECMWF solution plays out… sea surface temperatures in the region are below the 26 deg C threshold typically associated with tropical development… and upper air temps are currently and not forecast to become cold enough to de-stabilize the atmosphere (200 mb heights remaining above 1200 dekameters). Therefore tropical development of the surface low pressure southeast of Bermuda is not likely… and this is my only planned statement on this feature. Will resume daily birdseye view posts on the Atlantic tropics at the start of the next hurricane season on June 1 2022… or unless the potential for subtropical or tropical development returns to the Atlantic basin before then.