813 WTNT43 KNHC 050232 TCDAT3 Hurricane Sam Discussion Number 50 NWS National Hurricane Center Miami FL AL182021 300 AM GMT Tue Oct 05 2021 Sam's extratropical transition is well underway. The central core convection has decreased over the past several hours, with the telltale elongated cloud pattern forming on the northwestern side of the circulation. Still, AMSU-microwave data just before 00Z was very clear it is still has a healthy warm core, so advisories will continue. The initial wind speed is decreased to 75 kt, a bit above the satellite estimates. An approaching mid-latitude trough should cause Sam to quickly transition into a powerful extratropical cyclone within the next 6-12 hours while maintaining hurricane-force winds for about the next day. A slow weakening is expected after that time as Sam loses its baroclinic forcing. The only significant change from the last advisory is that models are in better agreement that Sam will become absorbed by another extratropical low in about 3 days, rather than be the dominant center, so the 96 h forecast is now dissipated. Sam is moving north-northeastward or 030/25 kt. The system is forecast to slow down as it merges with the mid-latitude trough. By late Tuesday, the post-tropical cyclone should turn east- northeastward before it moves northward and northwestward around the eastern portion of another trough/cut-off low over the north Atlantic. The latest NHC forecast is very close to the last one and the model consensus. Key Messages: 1. Swells generated by Sam will impact the northern Leeward Islands, the Greater Antilles, portions of the Bahamas, and southeastern Newfoundland through midweek. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 47.7N 40.2W 75 KT 85 MPH 12H 05/1200Z 50.6N 39.3W 70 KT 80 MPH...POST-TROP/EXTRATROP 24H 06/0000Z 51.0N 38.2W 65 KT 75 MPH...POST-TROP/EXTRATROP 36H 06/1200Z 51.5N 33.3W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 07/0000Z 54.0N 28.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 07/1200Z 58.0N 22.9W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 08/0000Z 61.5N 25.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 09/0000Z...DISSIPATED $$ Forecaster Blake