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Tropical Storm Fred Forecast Discussion Number 7
2021-08-11 10:46:52| National Hurricane Center (Atlantic)
Issued at 500 AM AST Wed Aug 11 2021 000 WTNT41 KNHC 110846 TCDAT1 Tropical Storm Fred Discussion Number 7 NWS National Hurricane Center Miami FL AL062021 500 AM AST Wed Aug 11 2021 Fred's satellite and radar presentation have changed little since it became a tropical storm yesterday evening. The system consists mainly of a circularly shaped area of deep convection with cloud tops colder than -70C on infrared images, with some rain bands trying to wrap around the center on radar images. The outer banding features have become indistinct on satellite imagery at the moment. Upper-level outflow remains well defined. Wind gusts to tropical storm force were reported at elevated sites at Cabo Rojo on the southwestern tip of Puerto Rico. The current intensity estimate is held at 35 kt, in agreement with Advanced Dvorak Technique estimates from UW-CIMSS. A west-northwestward motion appears to have resumed, at about 14 kt. The system should continue to move on this heading with a gradual decrease in forward speed, on the south side of a mid-level subtropical ridge, for the next 2-3 days. Around 72 hours, Fred should begin to turn to the right as it nears the western periphery of the ridge. During the next 3-5 days a generally northwestward track, toward a weakness in the ridge, is likely. The official forecast track is about the same as the previous one, and in good agreement with the latest TVCA and HCCA model consensus guidance. Again, users are advised that 4- and 5-day track forecasts have average errors of 175 and 200 miles, respectively. Although the vertical shear is currently low, which would normally be conducive for strengthening, the cyclone will soon begin to interact with the land mass of Hispaniola. This should cause some weakening later today and tonight. Some restrengthening should occur after the system moves away from that island. However, given the likely disruption of the circulation by the mountains, Fred may be slow to regain intensity. Moreover, an upper-level low and trough near Florida in 2-3 days could impart increasing west-southwesterly shear and limit intensification. The official intensity forecast is close to the model consensus and the LGEM guidance. As usual, there is significant uncertainty in the intensity forecast for the latter part of the period. KEY MESSAGES: 1. Tropical storm conditions are expected to begin in portions of the Dominican Republic this morning. Tropical storm conditions are possible in northern Haiti and the southeastern Bahamas by late today. 2. Heavy rainfall could lead to flash, urban, and small stream flooding, along with possible rapid river rises and the potential for mudslides across the U.S. Virgin Islands, Puerto Rico, and the Dominican Republic. The greatest threat for flooding impacts will be across eastern and southern Puerto Rico. 3. There is a risk of wind and rainfall impacts elsewhere in portions of Hispaniola, the Bahamas, and Cuba during the next few days, although the forecast is more uncertain than usual since Fred is forecast to interact with Hispaniola today. Interests in these areas should monitor Fred's progress and updates to the forecast. 4. There is a risk of wind and rainfall impacts in Florida beginning Friday in the Keys and spreading northward through portions of the Peninsula and the Panhandle this weekend. However, it is too soon to determine the exact timing, location, and magnitude of any potential impacts. Interests throughout Florida should monitor Fred's progress and check updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 18.0N 68.2W 35 KT 40 MPH 12H 11/1800Z 19.0N 70.2W 30 KT 35 MPH...INLAND 24H 12/0600Z 20.1N 72.5W 30 KT 35 MPH...OVER WATER 36H 12/1800Z 21.1N 74.7W 35 KT 40 MPH 48H 13/0600Z 22.1N 77.0W 35 KT 40 MPH 60H 13/1800Z 23.0N 79.0W 35 KT 40 MPH 72H 14/0600Z 24.1N 80.7W 40 KT 45 MPH 96H 15/0600Z 27.0N 83.0W 45 KT 50 MPH 120H 16/0600Z 29.5N 85.0W 55 KT 65 MPH $$ Forecaster Pasch
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