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Post-Tropical Cyclone Franklin Forecast Discussion



000
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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