[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 010856
TCDAT3

Hurricane Franklin Discussion Number  47
NWS National Hurricane Center Miami FL       AL082023
500 AM AST Fri Sep 01 2023

Franklin has a much more asymmetric appearance this morning,
indicative of the increasingly disruptive upper-wind pattern
associated with an approaching mid-latitude baroclinic zone.  In
fact, the remaining deep convective mass is about 100 mi southeast
of the surface center.  The initial intensity is lowered to 70 kt
and is based on a compromise of the available subjective and
objective intensity estimate techniques.

Franklin is showing signs of losing its tropical characteristics
while drier, more stable mid-level air and increasing northwesterly
shear impedes over the northwest portion of the cyclone.
Consequently, the completion of an extratropical transition is
expected later tonight or early Saturday.  However, little change in
strength is forecast, and Franklin should maintain its
hurricane-force sustained winds through the weekend.  By early next
week, gradual weakening is expected, which agrees with a blend of
the intensity consensus guidance and the statistical-dynamic SHIPS
models.

Franklin's initial motion is estimated to be east-northeastward or
060/16 kt.  An increase in forward speed toward the northeast is
forecast.  At the same time, Franklin moves within the mid-latitude
steering flow between high pressure to the east, over the central
Atlantic, and an extensive baroclinic system moving out of the
Canadian Maritimes.  Global model spread continues to increase
beyond day 3.  Two scenarios are possible.  The European models
take a southeastward track while interacting with a larger
cut-off low meandering west of the Iberian peninsula.  The other
solution involves the GFS and the regional guidance which gradually
turns the cyclone northeastward to northward over the northeast
Atlantic. The official forecast track indicates a blend of the two
model clusters, lying between both, and is close to the multi-model
consensus aid.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0900Z 37.8N  57.0W   70 KT  80 MPH
 12H  01/1800Z 39.1N  54.3W   70 KT  80 MPH
 24H  02/0600Z 41.2N  49.8W   70 KT  80 MPH...POST-TROP/EXTRATROP
 36H  02/1800Z 43.5N  45.5W   65 KT  75 MPH...POST-TROP/EXTRATROP
 48H  03/0600Z 45.7N  41.1W   60 KT  70 MPH...POST-TROP/EXTRATROP
 60H  03/1800Z 47.2N  36.6W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  04/0600Z 48.4N  32.8W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  05/0600Z 50.3N  27.9W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  06/0600Z 51.6N  25.0W   30 KT  35 MPH...POST-TROP/EXTRATROP

$$
Forecaster Roberts
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