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| #1063623 (Received by flhurricane at: 10:39 AM 28.Sep.2021) TCDAT3 Hurricane Sam Discussion Number 24 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Tue Sep 28 2021 Satellite images indicate that Sam has been generally steady in strength during the past several hours, and it remains a powerful category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. The storm has a well-defined eye, and the convective pattern surrounding the center is fairly symmetric. A 1043 UTC SSMIS pass showed a closed and symmetric eyewall, with no indication of a concentric eyewall. The latest Dvorak classifications from TAFB and SAB were 5.5/102 kt and the CIMSS automated technique is currently 6.2/120 kt. Based on these satellite estimates and the overnight reconnaissance data, the initial intensity is held at 115 kt. Another Air Force Hurricane Hunter aircraft is scheduled to investigate Sam this afternoon. The major hurricane is moving slowly northwestward, with the initial motion estimated to be 305/7 kt. A mid-level ridge situated to the north-northeast of Sam is expected to shift eastward as a deep-layer trough digs southeastward over the western Atlantic. This change in the large-scale pattern should cause Sam to speed up and gradually turn toward the north in 2 or 3 days and then to the northeast in 4 to 5 days. The models are in fairly good agreement, and the new forecast track is essentially an update of the previous one. Based on the forecast, Sam should pass well east of the northern Leeward Island through Wednesday and east of Bermuda Friday night and Saturday. Sam is expected to remain in favorable environmental conditions for it to maintain its intensity, or perhaps strengthen slightly, during the next day or two. However, after that time, a gradual increase in southerly shear should promote a slow weakening trend, and Sam will likely be beginning its transition to an extratropical cyclone toward the end of the forecast period. The NHC intensity forecast is also an update of the previous one and in line with the various consensus aids. Sam is expected to remain a major hurricane during the next several days. The initial wind radii have been adjusted based on a 1114 UTC ASCAT-A pass. Key Messages: 1. Large swells generated by Sam are affecting the Leeward Islands and will spread to portions of the Virgin Islands, Puerto Rico, Hispaniola, the Bahamas, and Bermuda by Thursday or Friday. Significant swells will likely reach the east coast of the United States and Atlantic Canada by the weekend. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials through the upcoming weekend. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 17.5N 54.3W 115 KT 130 MPH 12H 29/0000Z 18.2N 55.1W 120 KT 140 MPH 24H 29/1200Z 19.2N 56.5W 115 KT 130 MPH 36H 30/0000Z 20.5N 58.1W 115 KT 130 MPH 48H 30/1200Z 22.0N 59.6W 110 KT 125 MPH 60H 01/0000Z 24.0N 60.9W 110 KT 125 MPH 72H 01/1200Z 26.6N 61.5W 110 KT 125 MPH 96H 02/1200Z 32.5N 59.7W 100 KT 115 MPH 120H 03/1200Z 39.2N 54.8W 90 KT 105 MPH $$ Forecaster Cangialosi |
