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Potential Tropical Cyclone Twenty-Six Forecast Discussion Number 1
2020-10-04 23:02:19| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Sun Oct 04 2020 000 WTNT41 KNHC 042102 TCDAT1 Potential Tropical Cyclone Twenty-Six Discussion Number 1 NWS National Hurricane Center Miami FL AL262020 500 PM EDT Sun Oct 04 2020 Visible satellite imagery and earlier scatterometer data indicated that the circulation associated with the area of low pressure in the central Caribbean Sea has gradually become better defined. The associated deep convection does not yet have enough organization to classify the system as a tropical depression, but there has been some increase in convection just south of the estimated center. The earlier ASCAT data revealed peak winds of around 30 kt over the northeastern portion of the circulation, and that is the basis for the initial intensity. The disturbance is located over warm waters and in a moist environment, but there is some modest northeasterly shear over the system. The global models indicate that the shear will decrease overnight, and the oceanic and atmospheric environment is expected to quite favorable for both the development of a tropical cyclone and subsequent strengthening of the system over the northwestern Caribbean Sea during the next couple of days. The intensity guidance is quite aggressive, but also assumes that the system already has a tropical cyclone structure. Therefore, the NHC intensity forecast is a little below the intensity consensus during the first 24-48 hours, but does show the system at or near hurricane strength by the time is near western Cuba on Tuesday. Environmental conditions are expected to remain favorable for strengthening over the southeastern Gulf of Mexico, and additional strengthening is predicted during that time. Late in the period, conditions are forecast to become less conducive as the vertical wind shear increases and the system nears the cooler shelf waters of the northern Gulf of Mexico. The disturbance is moving west-northwestward or 290/9 kt. A mid- to upper-level ridge over the western Atlantic is forecast to build westward over the next few days, which should continue to steer the system west-northwestward to northwestward over the northwestern Caribbean Sea and southeastern Gulf of Mexico. The forward speed of the system is likely to increase in 48 to 72 hours while it moves between the ridge and Tropical Storm Gamma to its southwest. After 72 hours, the cyclone is forecast to slow down and turn northward around the western portion of the ridge and a mid- to upper-level trough over the south-central United States. The track guidance is in relatively good agreement during the first 48 to 72 hours, but there is increasing spread thereafter. Users are reminded that the average 4- and 5-day NHC track forecast errors are about 160 to 200 miles at those time periods. Key Messages: 1. Tropical storm conditions are expected in the Cayman Islands beginning late Monday, and a Tropical Storm Warning is in effect. 2. Dangerous storm surge and hurricane conditions are possible in portions of western Cuba and the Isle of Youth by Tuesday afternoon, and a Hurricane Watch is in effect. 3. Heavy rainfall will affect portions of Hispaniola, Jamaica, the Cayman Islands, and western Cuba during the next few days and could lead to life-threatening flash floods and mudslides. 4. The system is forecast to approach the northern Gulf Coast late this week as a hurricane. While there is large uncertainty in the track and intensity forecasts at these time ranges, there is a risk of dangerous storm surge, wind, and rainfall hazards along the coast from Louisiana to the western Florida Panhandle. Residents in these areas should monitor the progress of the system and check for updates to the forecast during the week. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 16.7N 76.6W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 05/0600Z 17.1N 77.7W 30 KT 35 MPH...TROPICAL DEPRESSION 24H 05/1800Z 18.0N 79.1W 35 KT 40 MPH 36H 06/0600Z 19.0N 80.5W 45 KT 50 MPH 48H 06/1800Z 21.0N 82.8W 60 KT 70 MPH 60H 07/0600Z 23.1N 85.4W 70 KT 80 MPH 72H 07/1800Z 24.7N 87.9W 80 KT 90 MPH 96H 08/1800Z 26.5N 90.3W 85 KT 100 MPH 120H 09/1800Z 28.6N 90.3W 85 KT 100 MPH $$ Forecaster Brown
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