[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 012040
TCDAT3

Post-Tropical Cyclone Franklin Discussion Number  49
NWS National Hurricane Center Miami FL       AL082023
500 PM AST Fri Sep 01 2023

The satellite appearance of Franklin suggests the cyclone has
undergone a warm core seclusion process. Earlier scatterometer data
showed a cold front nearing the core of Franklin, and recent visible
satellite images suggest the presence of a bent-back occlusion
wrapping around the western side of the low that appears to be the
focus for the ongoing convection. Also, the latest FSU phase space
diagrams from the GFS and ECMWF models show a thickness asymmetry
consistent with a warm-core frontal cyclone. Therefore, it appears
Franklin has completed its extratropical transition and is no longer
a tropical cyclone. Since the earlier scatterometer data, the latest
global model fields suggest that baroclinic forcing has resulted in
a deepening of the low, with an acceleration of northerly winds to
the west of the bent-back front. A blend of wind speeds from the
various global models supports an initial intensity of 70 kt.

Franklin appears likely to remain a powerful, hurricane-force
extratropical cyclone during the next 12 h or so due to baroclinic
forcing. Thereafter, the extratropical cyclone is forecast to weaken
as the low moves deeper into the mid-latitudes and gradually fills.
Franklin is still moving northeastward (50/15 kt) within the flow
between a deep-layer trough over the northwestern Atlantic and a
subtropical ridge over the central Atlantic. A faster northeastward
motion is forecast during the next couple of days, followed by a
gradual turn toward the east and east-southeast later in the
period as the cyclone rotates around a larger cut-off low over the
eastern Atlantic. The global models are finally in better agreement
on this outcome, and the track forecast has been adjusted south of
the previous one at days 3-5.

This is the last advisory issued by the National Hurricane Center on
Franklin. Additional information on this system can be found in High
Seas Forecasts issued by the National Weather Service, under AWIPS
header NFDHSFAT1, WMO header FZNT01 KWBC, and online at
ocean.weather.gov/shtml/NFDHSFAT1.php


FORECAST POSITIONS AND MAX WINDS

INIT  01/2100Z 39.5N  53.8W   70 KT  80 MPH...POST-TROPICAL
 12H  02/0600Z 41.1N  50.2W   70 KT  80 MPH...POST-TROP/EXTRATROP
 24H  02/1800Z 43.6N  45.6W   60 KT  70 MPH...POST-TROP/EXTRATROP
 36H  03/0600Z 45.5N  41.4W   50 KT  60 MPH...POST-TROP/EXTRATROP
 48H  03/1800Z 46.8N  36.7W   45 KT  50 MPH...POST-TROP/EXTRATROP
 60H  04/0600Z 47.8N  32.4W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  04/1800Z 48.0N  29.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  05/1800Z 47.5N  26.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  06/1800Z 46.0N  20.5W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Reinhart
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