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| #1064390 (Received by flhurricane at: 4:42 PM 03.Oct.2021) TCDAT3 Hurricane Sam Discussion Number 45 NWS National Hurricane Center Miami FL AL182021 500 PM AST Sun Oct 03 2021 Sam is a resilient hurricane despite having just crossed the 26 degrees C isotherm. An eye remains readily apparent in satellite imagery, while microwave images show a symmetrical concentric eyewall structure. Recent scatterometer data revealed that the tropical-storm-force wind field continues to expand, with these winds now extending 200 n mi or greater in all quadrants. A blend of the latest Dvorak intensity estimates from TAFB, SAB, and the UW-CIMMS ADT supports maintaining an initial advisory intensity of 85 kt. Gradual weakening is expected over the next 36 h as Sam moves over progressively cooler waters. However, the wind field is forecast to continue expanding. On Monday, the cyclone is expected to interact with a strong mid-level trough moving off the coast of Newfoundland which should cause Sam to transition into a powerful extratropical cyclone. With a lack of baroclinic forcing once Sam becomes vertically stacked with the trough in 48 h, the extratropical cyclone is expected to steadily weaken over the northern Atlantic through late this week. The latest NHC intensity forecast is little changed from the previous one, and is near the various model consensus solutions. Sam has begun to accelerate and is now moving 060/14 kt. A northwestward motion and continued acceleration is forecast through Monday as the cyclone gets caught in southwesterly flow ahead of the mid-level trough. Just before Sam merges with the trough in a couple of days, the cyclone should slow down as it pivots around the eastern flank of the trough. Thereafter, the merged system should continue northeastward then northward in the flow around a larger mid- to upper-level trough over the far northern Atlantic. The model guidance is in very good agreement on this track scenario, and the latest NHC track forecast remains near the previous one. Key Messages: 1. Swells generated by Sam will impact the northern Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, the eastern United States 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 03/2100Z 38.6N 52.8W 85 KT 100 MPH 12H 04/0600Z 40.3N 49.7W 80 KT 90 MPH 24H 04/1800Z 44.2N 44.3W 75 KT 85 MPH 36H 05/0600Z 49.0N 40.4W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 05/1800Z 50.8N 39.5W 65 KT 75 MPH...POST-TROP/EXTRATROP 60H 06/0600Z 51.5N 35.7W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 06/1800Z 53.2N 31.2W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 07/1800Z 59.4N 27.2W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 08/1800Z 61.2N 27.5W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto |
