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| #1063664 (Received by flhurricane at: 4:42 PM 28.Sep.2021) TCDAT3 Hurricane Sam Discussion Number 25 NWS National Hurricane Center Miami FL AL182021 500 PM AST Tue Sep 28 2021 Sam has looked a little less impressive on satellite imagery this afternoon, particularly on the infrared channels where the eye is not very well-defined. However, observations from the Air Force Hurricane Hunters indicate that the hurricane is maintaining category 4 intensity since a blend of the latest flight-level and SFMR-observed surface winds support maintaining 115-kt winds. The aircraft also measured a quite low central pressure of 947 mb on two passes through the eye. Upper-level outflow remains well defined except over the southwest quadrant of the circulation, and several arc clouds are seen emanating from the system over the western semicircle, indicative of some dry mid-level air in the environment. However, this dry air is apparently not significantly affecting the inner core of Sam, given that it has remained a powerful hurricane. Center fixes yield a continued slow northwestward motion of around 305/8 kt. There is little change to the track forecast reasoning from the previous advisories. Sam is likely to move around the southwestern periphery of a subtropical ridge for the next couple of days. A turn toward the north, ahead of a large mid-tropospheric trough moving off the United States east coast, is forecast around day 3. Later in the forecast period, the hurricane is expected to accelerate northeastward within the flow on the eastern side of the trough. There is good agreement among most of the guidance models on this general track, and the official forecast is very close to the model consensus. Since Sam will remain in a low-shear environment and over a warm ocean surface for the next few days, some re-intensification is possible, and the system is likely to remain a major hurricane for the next 4 days or so. The official intensity forecast is not much different from the latest NOAA corrected consensus forecast, HCCA. 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 28/2100Z 17.9N 55.0W 115 KT 130 MPH 12H 29/0600Z 18.6N 55.9W 120 KT 140 MPH 24H 29/1800Z 19.7N 57.4W 115 KT 130 MPH 36H 30/0600Z 21.0N 59.1W 115 KT 130 MPH 48H 30/1800Z 22.8N 60.6W 110 KT 125 MPH 60H 01/0600Z 25.0N 61.6W 110 KT 125 MPH 72H 01/1800Z 27.7N 62.0W 110 KT 125 MPH 96H 02/1800Z 33.5N 59.0W 100 KT 115 MPH 120H 03/1800Z 40.0N 53.5W 90 KT 105 MPH $$ Forecaster Pasch |