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Hurricane Sam Forecast Discussion Number 10
2021-09-25 04:34:49| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Sep 24 2021 444 WTNT43 KNHC 250234 TCDAT3 Hurricane Sam Discussion Number 10 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Fri Sep 24 2021 Sam developed a 10-n mi wide eye in infrared satellite images a few hours ago, surrounded by a ring of cloud tops as cold as about -70 degrees Celsius. The core of the hurricane remains compact. In fact, recent Synthetic Aperture Radar (SAR) data indicated that the radius of maximum winds is only about 6 n mi. Dvorak estimates were T5.0/90 kt from TAFB and T4.5/77 kt from SAB at 0000 UTC, and given the additional clearing of the eye since then, Sam's intensity is raised to 85 kt. Sam has been moving toward the west-northwest during the past 6 to 12 hours with a motion of 285/12 kt. The track forecast reasoning remains the same, and the model guidance is packed more tightly than normal through day 5. A blocking ridge lying to the north and northwest is expected to cause Sam to slow down over the weekend and maintain a motion toward the west or west-northwest. On days 3 through 5, the ridge is expected to shift eastward, with a deep-layer trough developing over the western Atlantic. This should allow Sam to turn northwestward toward the end of the forecast period. The NHC track forecast has not budged much and remains close to the TVCA consensus aid. Based on this forecast, and nearly all of the reliable guidance, Sam is expected to still be well to the east or northeast of the northern Leeward Islands through day 5. Deep-layer shear is expected to be less than 10 kt for the next day or two, and Sam will be heading toward waters of higher oceanic heat content. These conditions favor continued strengthening, and the hurricane is forecast to become a major hurricane on Saturday and possibly reach a peak intensity in 2 to 3 days. For this period, the NHC forecast is close to the HCCA consensus aid and is near the high end of the guidance envelope. As is usually the case with hurricanes this small and strong, fluctuations in intensity due to eyewall replacement cycles will be possible. On days 3 through 5, some increase in shear as Sam approaches the deep-layer western Atlantic trough is possible, and modest weakening is shown at those times. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 12.4N 45.9W 85 KT 100 MPH 12H 25/1200Z 12.7N 47.4W 100 KT 115 MPH 24H 26/0000Z 13.1N 48.8W 110 KT 125 MPH 36H 26/1200Z 13.5N 50.0W 115 KT 130 MPH 48H 27/0000Z 14.1N 51.2W 120 KT 140 MPH 60H 27/1200Z 14.8N 52.4W 120 KT 140 MPH 72H 28/0000Z 15.7N 53.5W 115 KT 130 MPH 96H 29/0000Z 17.4N 55.8W 110 KT 125 MPH 120H 30/0000Z 19.5N 58.8W 110 KT 125 MPH $$ Forecaster Berg
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