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SNE "Tropical" Season Discussion 2020


Bostonseminole
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Well, ... to point out the obvious - 

The GFS has a hurricane as a coherently separate phenomenon ... captured and evacuating up astride the EC on that frame...   Contrasting, the Euro does not carry said feature - at all. 

The Euro's depiction is a purely en route to formulating an extratropical cyclogenesis, with perhaps an argument not worth having for some sort of weakly establishing yet doomed TD in the process of being evacuated out of the subtropics amid the barotropic conveyor ... that's a bug just before the windshield at 70 mph there..  

Typically... full bird matured hurricanes and extratropical cyclones do not present with the same pressure pattern morphology on a weather map - it's like the difference between looking at a galaxy from a billion light years away, vs a tight, close spectral analysis of the quasar at said galaxies nucleus ...where the gradient of space time is severely sloped.   But in more practical terms, the ballast of the upward vertical momentum of TC is near the core; where as, baroclinic lows ...which derive their mechanical forcing from larger synoptic jet mechanics ..are by virtue thus spread out.   Sometimes, ... a uniquely intersecting jet fields will pass over unusually, vertically sloped low level thickness gradient...causing very upright air parcel motion where said jets happen across that gradient. The diffluence requires huge restoring mass to lift, but as it passes over the upright structure ... this gives the UVM exceptionally efficient conversion of psuedo-adiabatic heat release into velocity - and that will drive excessive internal pressure falls: 'bombogenesis' as it were... This may transiently take-on a pressure pattern structures that mimics the orientation of tropical cyclone phenomenon - but usually as the low "maxes" out, the internal pressure may stabilize, while remaining deep, and associated wind/response both expand so there is more proportional layout between the intervals between the core and the outer periphery of the low.   

 

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...that said, the Euro does at least set the table for an usual event ...

It is interesting to see that with the Euro's pretty clear bias of meridional flow exaggeration in its extended range ( in this case ...way out there, notwithstanding), vs the GFS ...which has a velocity rich bias causing a longitudinal stretching all the way up to the R-wave scales ... ( causing an opposing end state usually ) they've still managed to animate similar deep full latitude trough anomaly through that spatial-temporal range.   

The GFS happens to have a hurricane ...and as we all know, has been occasionally entangling one precariously near or into said trough for many cycles now - just not consistently in positoin or time but ...that's a forgone conclusion when modeling day 12 and beyond ( geez) ...

Anyway, should the Euro come around to the growing consensus for some form of western Caribbean TC ... any said realization probably also feels the steering influence and gets evacuated out ... it doesn't take a huge leap of visionary insight to imagine any such feature as being rail-roaded along a similar precarious circumstance.  

So ...in simple terms, the period of time should be watched.  

Either way, just noting... according to recent trends/modalities of CPC's various teleconnectors.. there is a concerted rising motion in the PNA and NAO out through week two - that tends to herald a time for troughing over eastern N/A.   Plus, climo for TC and trough marriages is hot through late November anyway ...so there's that -

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