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Hurricane Sam Forecast Discussion Number 46
2021-10-04 04:34:16| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Oct 03 2021 000 WTNT43 KNHC 040234 TCDAT3 Hurricane Sam Discussion Number 46 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Sun Oct 03 2021 Sam still had a surprise up its sleeve tonight, with its eye becoming warmer on satellite images along with a stronger eyewall. Microwave data from earlier today indicated that Sam has been undergoing a concentric eyewall cycle, and it appears that the inner eyewall has become better defined. Regardless, it is not every day you see a hurricane with that clear of an eye near 40N, and the intensity estimates the evening range from 90-100 kt. Given the concentric eyewalls, the initial wind speed is conservatively raised to 90 kt, but it could be higher. High-resolution NOAA OISST data indicate that Sam is moving near a warm eddy along the north wall of the Gulf Stream. This favorable factor, in addition to low shear, should keep Sam's weakening to a minimum in the near term. Later on, although the shear increases rapidly and SSTs fall quickly, Sam is expected to transition into a powerful extratropical cyclone late Monday or early Tuesday due to a mid-latitude trough interaction well east of Newfoundland. This should cause extratropical Sam to maintain hurricane-force winds until early Wednesday. A slow weakening is expected thereafter as it slowly spins down as an occluded low. No significant changes were made to the previous forecast. Sam is moving faster, now 050/17 kt. A northeastward motion and continued acceleration is forecast through Monday as the cyclone gets caught in southwesterly flow ahead of the mid-latitude trough. The tropical cyclone is expected to be the main surface low center as it merges with the trough in a couple days, hooking briefly to the left. Thereafter, the system should resume a northeastward motion and gradually turn northward and even westward at long range as it moves around another trough. Model guidance is close to the previous cycle, even with the loopy track, and the new NHC forecast is basically just an update of the last advisory. 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 04/0300Z 39.3N 51.2W 90 KT 105 MPH 12H 04/1200Z 41.6N 47.3W 85 KT 100 MPH 24H 05/0000Z 46.5N 42.1W 75 KT 85 MPH 36H 05/1200Z 50.4N 40.3W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 06/0000Z 50.8N 38.3W 65 KT 75 MPH...POST-TROP/EXTRATROP 60H 06/1200Z 51.6N 33.3W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 07/0000Z 54.5N 28.2W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 08/0000Z 61.0N 28.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 09/0000Z 61.5N 32.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake
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