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Hurricane Sam Forecast Discussion Number 44
2021-10-03 16:47:32| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Oct 03 2021 000 WTNT43 KNHC 031447 TCDAT3 Hurricane Sam Discussion Number 44 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Sun Oct 03 2021 Sam's cloud pattern remains quite symmetric for a hurricane moving into the higher latitudes. The eye has become more apparent in both visible and infrared satellite imagery over the past few hours. A very timely 1155 UTC GMI microwave image also reveals a well-defined inner eye that was surrounded by an outer ring of convection at a much larger radius. A blend of the T- and CI-numbers from the lastest subjective Dvorak classifications yields an initial intensity of 85 kt, this is also supported by earlier UW/CIMSS SATCON estimates. The vertical shear over Sam is expected to remain low for the next 6-12 hours and only gradual weakening is anticipated while the system moves over gradually decreasing SSTs. Later tonight, Sam is expected to move over much cooler waters north of the north wall of the Gulf Stream and into an area of increasing southwesterly shear, which should result in continued weakening. However, a strong mid-tropospheric trough approaching Sam from the west on Monday is expected to result in a fairly quick transition of Sam to a large and powerful extratropical low. The low is forecast to gradually weaken over the far north Atlantic during the middle to latter portions of the week as the baroclinic forcing decreases. The latest NHC intensity forecast is similar to the previous advisory and is a blend of the various intensity aids during the early portion of the period, but leans toward the global model guidance during the post-tropical phase. Sam is moving northeastward or 050/14 kt. The cyclone should continue to move northeastward in the flow between a strong subtropical ridge over the eastern Atlantic and mid-latitude trough over Atlantic Canada. As this trough approaches Sam from the west, a much faster northeastward motion is expected by Monday and Monday night. Around midweek, the post-tropical cyclone is forecast to slow down as it rotates around a large cut-off low over the north Atlantic. After that time, the low is forecast to resume a northeastward motion before it slows once again to the southwest of Iceland. Given the future complex interactions of the post-tropical low with the cut-off low and trough over the north Atlantic, the track guidance is in surprisingly good agreement, and the NHC forecast is near a blend of the ECMWF and GFS global models. 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 03/1500Z 37.7N 54.6W 85 KT 100 MPH 12H 04/0000Z 39.3N 51.9W 80 KT 90 MPH 24H 04/1200Z 42.4N 47.0W 75 KT 85 MPH 36H 05/0000Z 47.0N 41.7W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 05/1200Z 50.9N 39.8W 65 KT 75 MPH...POST-TROP/EXTRATROP 60H 06/0000Z 50.9N 38.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 06/1200Z 51.5N 33.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 07/1200Z 59.2N 27.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 08/1200Z 60.5N 31.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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