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Post-Tropical Cyclone GABRIELLE


Post-Tropical Cyclone Gabrielle Discussion Number  11
NWS National Hurricane Center Miami FL       AL082019
500 AM AST Fri Sep 06 2019

Poorly defined Gabrielle has not produced any organized deep
convection since Thursday morning, and what remains of the showers
and thunderstorms, is displaced nearly 200 miles north of the
elongated surface circulation.  Consequently, Gabrielle can no
longer be classified as a tropical cyclone and has degenerated into
a 35 kt post-tropical cyclone.

Statistical-dynamical models, as well as the large-scale guidance,
show that strong shear, along with mid-tropospheric dry air
intrusion, should continue to inhibit convective development during
the next 24 h or so, and cause further weakening into a remnant
low. Around mid-period, the shear is forecast to decrease and the
upper wind pattern becomes more diffluent. Additionally,
Post-Tropical Cyclone Gabrielle will be traversing significantly
warmer oceanic sea surface temperatures.  As a result, the cyclone
is forecast to redevelop organized deep convection, and more than
likely, re-strengthen.  In fact, some of the intensity guidance
shows Gabrielle becoming a hurricane in 4 days before transitioning
into an extratropical cyclone at the end of the period.  The NHC
intensity forecast is based on a blend of the HFIP HCCA, and the
deterministic guidance beyond day 3.

The initial motion is estimated to be an accelerating northwestward
motion, or 315/10 kt.  The global and regional models are in rather
good agreement that the post-tropical cyclone will gradually turn
toward the west-northwest during the next 48 hours, before recurving
northward and then northeastward early next week in response to an
approaching major shortwave mid-latitude trough from the northwest.
The official forecast track is just a little to the left of the
previous one, and is very close to the TVCA simple multi-model


INIT  06/0900Z 25.5N  37.6W   35 KT  40 MPH...POST-TROPICAL
 12H  06/1800Z 27.1N  39.2W   30 KT  35 MPH...POST-TROP/REMNT LOW
 24H  07/0600Z 29.2N  41.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 36H  07/1800Z 30.7N  44.8W   35 KT  40 MPH...TROPICAL CYCLONE
 48H  08/0600Z 31.9N  47.4W   45 KT  50 MPH
 72H  09/0600Z 35.6N  48.6W   55 KT  65 MPH
 96H  10/0600Z 40.4N  44.3W   60 KT  70 MPH
120H  11/0600Z 47.0N  34.5W   55 KT  65 MPH...POST-TROP/EXTRATROP

Forecaster Roberts