000 WTNT43 KNHC 021451 TCDAT3 Hurricane Sam Discussion Number 40 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Sat Oct 02 2021 Sam has been an impressive hurricane during the past several days. The latest satellite imagery shows it remains a powerful system, with a well-defined eye and symmetric cloud pattern. In fact, since the plane left overnight, the eye has actually warmed, with little change in the eyewall convection. Thus the initial intensity will stay 115 kt, above the latest satellite classifications, but consistent with the earlier aircraft data and low bias of the Dvorak technique for much of the this storm. Sam is now in the top 10 for consecutive days as a category 4 hurricane or greater in the historical record, about the same as Matthew 2016. The hurricane is forecast to gradually lose strength during the next 36 hours or so while it remains over marginally warm waters, but in fairly light shear. In fact, some of the guidance decrease the shear overnight, which should allow Sam to keep much of its strength, provided it doesn't undertake an eyewall cycle. The new intensity forecast is higher in the first day or so, consistent with the latest model solutions. In about 2 days, Sam will cross the north wall of the Gulf Stream, and in 3 days is expected to spectacularly transition into a large hurricane-force post-tropical cyclone over the far north Atlantic. No changes were made to the end of the intensity forecast. Sam has turned northeastward at about 15 kt. The hurricane should accelerate later this weekend due to increasing flow between a deep-layer ridge to the east and a large mid- to upper-level low over Atlantic Canada. By midweek the system is forecast to turn more to the north-northeast as it becomes a spoke in a very large extratropical low over the far North Atlantic. The new forecast has shifted somewhat eastward during the first couple of days but ends up very near the last advisory by day 5. Key Messages: 1. Swells generated by Sam will impact the northern Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, the eastern United States coast and Atlantic Canada for the next couple of days. 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 02/1500Z 33.9N 59.3W 115 KT 130 MPH 12H 03/0000Z 35.6N 57.8W 105 KT 120 MPH 24H 03/1200Z 37.4N 55.3W 100 KT 115 MPH 36H 04/0000Z 39.2N 52.0W 95 KT 110 MPH 48H 04/1200Z 41.8N 47.3W 85 KT 100 MPH 60H 05/0000Z 46.0N 42.0W 80 KT 90 MPH 72H 05/1200Z 50.0N 38.5W 75 KT 85 MPH...POST-TROP/EXTRATROP 96H 06/1200Z 53.0N 33.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 07/1200Z 59.0N 26.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake