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| #1064318 (Received by flhurricane at: 4:59 AM 03.Oct.2021) TCDAT3 Hurricane Sam Discussion Number 43 NWS National Hurricane Center Miami FL AL182021 500 AM AST Sun Oct 03 2021 Sam has continued to weaken since the previous advisory, with cloud tops in the central dense overcast (CDO) having warmed to -60 to -65 deg C near the center. However, the upper-level outflow pattern remains impressive The initial intensity has been lowered to 90 kt based on an average of the current data-T number of 4.5/77 kt and current intensity (CI) estimate of 5.5/102 kt from TAFB, and a 0530 UTC UW-CIMSS SATCON intensity estimate of 89 kt. Further weakening during the is expected as Sam moves over progressively cooler water and southwesterly vertical wind shear of 20-25 kt continues. By 18-24 hours, Sam will be moving north of the north wall of the Gulfstream, resulting in extratropical transition due to the cyclone moving over sub-20-deg-C sea-surface temperatures. However, favorable interaction with a strong mid-tropospheric trough will result in Sam becoming a large and powerful extratropical low with hurricane-force winds in 36-48 hours. Thereafter, Sam`s wind field is expected gradually spin down over the far north Atlantic when baroclinic forcing will cease. he new intensity forecast is similar to but slightly lower than the previous intensity forecast. The initial motion is northeastward, or 045/15 kt. The latest NHC model guidance is tightly clustered around the previous track forecast, and thus, no significant changes were made to the previous advisory track. A faster northeastward motion is expected during the next couple of days, followed by a slow down in the forward motion as Sam becomes entangled with an upper-level cutoff low. The new track forecast is essentially down the middle of the tightly packed simple and corrected-consensus models. Recent ASCAT-A surface wind data indicate that no significant adjustments to the 34- and 50-kt wind radii were needed, but that the size of the 64-kt wind radii had to be decreased somewhat. 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 03/0900Z 37.3N 55.9W 90 KT 105 MPH 12H 03/1800Z 38.6N 53.6W 85 KT 100 MPH 24H 04/0600Z 41.1N 49.4W 75 KT 85 MPH 36H 04/1800Z 44.9N 44.1W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 05/0600Z 49.5N 40.6W 65 KT 75 MPH...POST-TROP/EXTRATROP 60H 05/1800Z 51.4N 39.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 06/0600Z 52.0N 36.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 07/0600Z 57.0N 26.9W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 08/0600Z 60.5N 29.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart |
