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Hurricane Sam Forecast Discussion Number 11
2021-09-25 10:31:24| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 25 2021 000 WTNT43 KNHC 250831 TCDAT3 Hurricane Sam Discussion Number 11 NWS National Hurricane Center Miami FL AL182021 500 AM AST Sat Sep 25 2021 Sam continues to rapidly intensify. Geostationary satellite and microwave images show that the storm has a very small and distinct eye surrounded by a nearly symmetric ring of cold cloud tops. The latest Dvorak estimates range from 90 to 102 kt, and based on that data, the initial intensity is increased to 95 kt. Although Sam is nearly a major hurricane, it remains quite compact with tropical-storm-force and hurricane-force winds estimated to only extend 50 n mi and 15 n mi from the center, respectively. The hurricane is moving west-northwestward at 11 kt and is currently being steered by a mid-level ridge to its north. There has been little change to the track forecast philosophy or model guidance. Sam is expected to continue west-northwestward during the next two or three days, but it is forecast to move at a notably slower pace of 6-8 kt during most of that time period. After that time, the ridge is expected to shift eastward as a deep-layer trough becomes established over the western Atlantic. This change in the steering pattern should cause Sam to turn northwestward and speed up some by the middle of next week. The models are in fairly good agreement, and the NHC track forecast is largely an update of the previous one. 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. Continued steady or rapid strengthening is expected during the next day or two as the hurricane remains in near ideal conditions of very low wind shear and warm 29 deg C waters. However, beyond that time the shear is expected to increase a little, and that will likely cause Sam to level off in strength or weaken slightly next week. The NHC intensity forecast is slightly above the models in the short term, given the impressive structure of the hurricane and favorable conditions, but falls in line with the consensus aids at the longer lead times. Regardless of how strong Sam gets, nearly all of the models indicate that it will remain a powerful hurricane during the next several days. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 12.8N 46.7W 95 KT 110 MPH 12H 25/1800Z 13.1N 48.0W 110 KT 125 MPH 24H 26/0600Z 13.5N 49.3W 115 KT 130 MPH 36H 26/1800Z 14.0N 50.4W 120 KT 140 MPH 48H 27/0600Z 14.7N 51.5W 120 KT 140 MPH 60H 27/1800Z 15.4N 52.5W 115 KT 130 MPH 72H 28/0600Z 16.3N 53.7W 115 KT 130 MPH 96H 29/0600Z 18.0N 56.0W 110 KT 125 MPH 120H 30/0600Z 20.1N 59.0W 110 KT 125 MPH $$ Forecaster Cangialosi
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