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Hurricane Sam Forecast Discussion Number 32
2021-09-30 16:55:31| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Sep 30 2021 000 WTNT43 KNHC 301455 TCDAT3 Hurricane Sam Discussion Number 32 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Thu Sep 30 2021 Sam continues to look quite impressive on satellite images, with a 20-25 n mi wide eye surrounded by very deep convection. The system's convective banding features and upper-level anticyclonic outflow also remain well-defined, with particularly strong outflow to the northwest and north. Subjective and objective Dvorak intensity estimates have not changed significantly since earlier this morning, so the advisory intensity will remain at 125 kt. Interestingly, aircraft observations show that Sam has been a little stronger than indicated by satellite-derived intensity estimates, which underscores the value of aerial reconnaissance of tropical cyclones. Another Air Force Hurricane Hunter aircraft is scheduled to investigate the hurricane later today. Sam should continue to move over waters of high oceanic heat content and within a low-shear atmospheric environment for the next 24 hours or so. Thus, it could still strengthen a little today and tonight. By 48 hours, decreasing SSTs and increasing shear should lead to a gradual weakening trend. Around day 5, global model fields suggest that Sam will be merging with a baroclinic zone and transition into a large and powerful extratropical cyclone over the north Atlantic. The official intensity forecast is in good agreement with the HCCA corrected consensus model prediction. The hurricane is moving a little faster toward the northwest, or at about 320/11 kt. During the next couple of days, a gradual turn toward the north is likely as Sam rounds the western end of a large subtropical anticyclone over the eastern and central Atlantic. Thereafter, Sam is forecast to move generally northeastward in the flow between the anticyclone and a trough near Atlantic Canada. The NHC forecast is very similar to a consensus of the typically reliable GFS and ECMWF predictions, with a little bit of smoothing around days 3-4. Although the core of Sam is forecast to pass east of Bermuda early Saturday, the tropical-storm-force wind field is forecast to expand and could pass very close to the island beginning late Friday night or early Saturday. Therefore, a Tropical Storm Watch is in effect for Bermuda. Key Messages: 1. Swells generated by Sam will impact the Northern Leeward Islands and the Greater Antilles, including Puerto Rico, during the next few days. Swells are expected to reach Bermuda and the Bahamas by Friday, and then spread to the United States east coast by this weekend. 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 Friday night or early Saturday, and a Tropical Storm Watch has been issued for that island. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 22.6N 60.0W 125 KT 145 MPH 12H 01/0000Z 24.4N 60.8W 130 KT 150 MPH 24H 01/1200Z 27.2N 61.7W 125 KT 145 MPH 36H 02/0000Z 30.2N 61.6W 115 KT 130 MPH 48H 02/1200Z 32.7N 60.8W 105 KT 120 MPH 60H 03/0000Z 34.9N 59.2W 95 KT 110 MPH 72H 03/1200Z 36.9N 57.0W 90 KT 105 MPH 96H 04/1200Z 40.0N 51.0W 80 KT 90 MPH 120H 05/1200Z 44.5N 45.5W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch
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