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| #1056193 (Received by flhurricane at: 11:00 PM 09.Aug.2021) TCDAT1 Potential Tropical Cyclone Six Discussion Number 2 NWS National Hurricane Center Miami FL AL062021 1100 PM AST Mon Aug 09 2021 The disturbance is now very near the Leeward Islands and it is expected to produce gusty winds and heavy rains across portions of those islands during the next several hours. Satellite and radar data indicate that deep convection continues to gradually organize in curved bands across the northern half of the circulation, but the system still seems to lack a well-defined center. Therefore, the disturbance remains a potential tropical cyclone for now. The initial intensity is held at 30 kt based on Dvorak estimates from TAFB and SAB. The system is moving west-northwestward at about 14 kt. The main steering feature for the system will continue to be the subtropical ridge that is situated to its north across the central and western Atlantic. The flow on the south side of the ridge should keep the depression moving relatively briskly to the west-northwest during the next couple of days, taking it across the Leeward Islands overnight, near or over the U.S. Virgin Islands and Puerto Rico Tuesday and Tuesday night, and then near or over Hispaniola on Wednesday. Beyond that time, the storm is forecast to gradually slow down, when it nears the southwestern portion of the ridge, as it moves near Cuba and the Bahamas late this week. By the weekend, most of the models show the depression reaching a weakness in the ridge, which will likely cause a gradual turn to the right near the Florida Keys or southern Florida. The models are in quite good agreement, especially during the next 3 or 4 days, and the NHC track forecast lies near the various consensus models. Users are reminded that the average track errors at days 4 and 5 are 175 miles and 200 miles, respectively. The disturbance is currently in conducive conditions for intensification with the cyclone currently over fairly warm 28 C waters and in low wind shear conditions. The only negative factor for the storm is some dry air in its vicinity. Overall, these environmental factors, and the model guidance, support strengthening during the next 24 hours or so, but the potential land interaction with Puerto Rico could limit the amount of intensification. By Wednesday, the potential land interaction with the mountainous island of Hispaniola and an increase in westerly shear should cause some weakening. However, the environmental conditions could become more favorable for strengthening again by the end of the week, which is the reason why the forecast shows slightly higher wind speeds at those time periods. The NHC intensity forecast generally follows the IVCN and HCCA models, which are typically the most skillful aids. It should be noted that the intensity forecast is of low confidence since the cyclone`s future strength will be quite dependent on the exact track and the degree of land interaction. KEY MESSAGES: 1. The system is forecast to become a tropical storm as it moves through the Leeward Islands tonight, and tropical storm conditions are possible there. Tropical storm conditions are expected in portions of the U.S. Virgin Islands and Puerto Rico beginning Tuesday afternoon, and in the Dominican Republic by Wednesday. Tropical storm conditions are possible in northern Haiti by late Wednesday. 2. Heavy rainfall could lead to flash, urban, and small stream flooding and potential mudslides across the U.S. Virgin Islands and Puerto Rico. The greatest threat for flooding impacts will be across the eastern and southeastern portions of Puerto Rico. 3. There is a risk of wind and rainfall impacts elsewhere in portions of Hispaniola, the Turks and Caicos, the southeastern Bahamas, and Cuba later this week, although the forecast is more uncertain than usual since the system is still in its formative stage. Interests in these areas should monitor the system`s progress and updates to the forecast. 4. Interests in the remainder of the Bahamas and Florida should monitor updates to the forecast for this system, but it is too soon to determine what if any impacts could occur there by late this week or this weekend given the uncertainty in the long-range forecast. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 15.1N 60.8W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 10/1200Z 16.2N 63.1W 35 KT 40 MPH...TROPICAL CYCLONE 24H 11/0000Z 17.5N 66.0W 45 KT 50 MPH 36H 11/1200Z 18.7N 68.8W 40 KT 45 MPH...INLAND 48H 12/0000Z 19.9N 71.5W 35 KT 40 MPH...INLAND 60H 12/1200Z 20.9N 74.0W 35 KT 40 MPH...OVER WATER 72H 13/0000Z 21.7N 76.1W 35 KT 40 MPH 96H 14/0000Z 23.4N 79.9W 40 KT 45 MPH 120H 15/0000Z 26.1N 82.4W 45 KT 50 MPH $$ Forecaster Cangialosi |