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Hurricane Sam Forecast Discussion Number 36
2021-10-01 16:52:51| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Fri Oct 01 2021 000 WTNT43 KNHC 011452 TCDAT3 Hurricane Sam Discussion Number 36 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Fri Oct 01 2021 Sam remains a powerful category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale over the subtropical central Atlantic. Satellite images show that the hurricane still has a circular and quite distinct eye and closed eyewall. However, an 0827 UTC SSMIS pass indicated that a dry slot was present on the eastern side of the circulation between the eyewall and rainbands. The latest Dvorak classifications from TAFB, SAB, and CIMSS at the University of Wisconsin range from 102-115 kt. However, Air Force reconnaissance data from earlier this morning showed that the winds were much higher, and in fact, the Dvorak estimates have had a low bias compared to the Hurricane Hunter data for the past 24-36 hours. Therefore, the initial intensity is held at 130 kt for now. Another Air Force Hurricane Hunter aircraft is scheduled to investigate Sam this afternoon. An ASCAT-A pass from around 12Z indicated that Sam's tropical-storm-force wind radii have expanded, and the initial wind radii were adjusted based on that data. In addition, the eye of Sam passed about 60 n mi east of NOAA buoy 41049 earlier this morning. The buoy reported a minimum pressure of 998 mb, maximum winds of around 45 kt, gusts to 62 kt, and maximum seas of about 22 ft. The major hurricane has turned to the north and is now moving faster. The latest initial motion estimate is 355/18 kt. The large-scale pattern consists of a deep-layer ridge to the northeast of Sam and a large low pressure system centered over Atlantic Canada. The steering flow between these features should cause Sam to move northeastward at a sightly slower pace this weekend. By early next week, the deep-layer low is expected to retreat northward, which should cause Sam to turn a little more to the right. The models are in fairly good agreement, but there are some notable speed differences with the UKMET model being a fast outlier. The new NHC track forecast is slightly to the right of the previous one at 60 and 72 h, but is otherwise very similar. This forecast lies near the middle of the guidance envelope. Sam is expected to slowly weaken during the next several days as it moves over progressively cooler waters and into an environment of stronger shear. The hurricane will likely begin extratropical transition in a couple of days when it crosses the 26 degree C isotherm, and this transition is expected to be completed by 96 hours. All of the model guidance shows steady weakening through the forecast period, and so does the NHC forecast. This prediction is close to the IVCN, IVDR, and HCCA models in the short term and near the GFS model during the extratropical portion of the forecast. Even though Sam is likely to weaken, it is still expected to be a significant storm over the next several days. Key Messages: 1. Swells generated by Sam will impact the northern Leeward Islands and the Greater Antilles, including Puerto Rico, during the next couple of days. Swells are expected to reach Bermuda and the Bahamas this afternoon, and then spread to the United States east coast and Atlantic Canada on Saturday. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. 2. Tropical storm conditions are possible on Bermuda beginning tonight or early Saturday, and a Tropical Storm Warning is in effect for the island. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 28.4N 61.8W 130 KT 150 MPH 12H 02/0000Z 30.7N 61.5W 125 KT 145 MPH 24H 02/1200Z 33.4N 60.2W 110 KT 125 MPH 36H 03/0000Z 35.6N 58.4W 100 KT 115 MPH 48H 03/1200Z 37.2N 56.0W 95 KT 110 MPH 60H 04/0000Z 38.7N 52.9W 90 KT 105 MPH 72H 04/1200Z 41.9N 48.6W 85 KT 100 MPH 96H 05/1200Z 49.0N 42.2W 75 KT 85 MPH...POST-TROP/EXTRATROP 120H 06/1200Z 51.0N 34.3W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi/Nepaul
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