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| #1056260 (Received by flhurricane at: 10:57 AM 10.Aug.2021) TCDAT1 Potential Tropical Cyclone Six Discussion Number 4 NWS National Hurricane Center Miami FL AL062021 1100 AM AST Tue Aug 10 2021 Satellite imagery shows that the disturbance has become better organized since yesterday, and satellite intensity estimates from TAFB and SAB are at tropical storm strength. However, reports from a NOAA Hurricane Hunter aircraft and surface observations indicate that the system does not yet have a well-defined closed circulation, with the wind and pressure fields more resembling an open wave, The maximum flight-level winds at 925 mb were 35-40 kt, and reliable SFMR wind estimates were near 30 kt. Based on these data, the system remains at potential tropical cyclone status with an initial intensity of 30 kt. The initial motion remains west-northwestward or 295/16 kt. A strong low- to mid-level ridge to the north should steer the system generally west-northwestward for the next 72 h with some decrease in forward speed after 24 h. Beyond that time, a turn toward the northwest with an further decrease in forward speed is likely while the system moves near the western periphery of the ridge. The track guidance has changed little since the previous advisory. So, the new NHC track also has little change, and it 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. Conditions continue to appear favorable for strengthening before the system reaches Hispaniola in about 24 h, although there may be dry air entraining into the system in the southeastern quadrant. The intensity forecast will follow the previous prediction in calling for the disturbance to become a tropical storm before landfall, followed by weakening to a depression. The remainder of the intensity forecast has lower confidence due to possible land interaction with Cuba and differences in the upper-level wind forecasts among the various global models. The new intensity forecast will call for slow intensification from 60 h onward, similar to the previous one. KEY MESSAGES: 1. The system is forecast to become a tropical storm as it moves over the northeastern Caribbean Sea today or tonight Tropical storm conditions are expected in portions of the U.S. Virgin Islands and Puerto Rico beginning this afternoon, and in the Dominican Republic by Wednesday. Tropical storm conditions are possible in northern Haiti and the southeastern Bahamas by late Wednesday. 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 and Puerto Rico. The greatest threat for flooding impacts will be across the eastern and southern portions of Puerto Rico. 3. There is a risk of wind and rainfall impacts elsewhere in portions of Hispaniola, the 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 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 10/1500Z 16.3N 63.8W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 11/0000Z 17.3N 66.1W 35 KT 40 MPH...TROPICAL CYCLONE 24H 11/1200Z 18.5N 68.9W 40 KT 45 MPH...INLAND 36H 12/0000Z 19.6N 71.4W 30 KT 35 MPH...INLAND 48H 12/1200Z 20.7N 73.9W 30 KT 35 MPH...OVER WATER 60H 13/0000Z 21.7N 76.0W 35 KT 40 MPH 72H 13/1200Z 22.7N 78.1W 35 KT 40 MPH 96H 14/1200Z 25.0N 82.0W 40 KT 45 MPH 120H 15/1200Z 27.5N 84.0W 50 KT 60 MPH $$ Forecaster Beven |
