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| #1150868 (Received by flhurricane at: 4:47 PM 01.Sep.2023) 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 |
