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Potential Tropical Cyclone Nine Forecast Discussion Number 5
2020-07-29 16:51:14| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Jul 29 2020 390 WTNT44 KNHC 291450 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 5 NWS National Hurricane Center Miami FL AL092020 1100 AM AST Wed Jul 29 2020 Surface observations from the Lesser Antilles show that the broader circulation of the disturbance has become slightly better defined but a recent Air Force Reserve reconnaissance aircraft was still unable to find a well-defined circulation. Therefore, the system has not yet become a tropical cyclone. The aircraft measured peak flight-level winds of 46 kt and several SFMR winds of around 35 kt, so the initial intensity remains 40 kt for this advisory. The system continues moving briskly west-northwestward at 290/20 kt. The forecast reasoning remains unchanged as a ridge to the north of the system is expected to steer the disturbance west-northwestward during the next couple of days. This motion should bring the system near or over Hispaniola on Thursday and near eastern Cuba Thursday night and Friday. The ridge is forecast to weaken by the weekend which should cause a reduction in forward speed. It still must be stressed that since the system lacks a well-defined center and remains in its formative stage, uncertainty in the specifics of the track forecast remain high in both the short and longer range. The latest NHC track foreast has been nudged slightly south of the previous advisory and lies between the latest ECMWF solution and the various consensus aids. Deep convection has consolidated and there is some evidence of banding over the northern and western portions of the large circulation. As a result, the system is still expected to become a tropical storm later today or tonight. Some additional intensification is then possible before the system reaches Hispaniola on Thursday, but weakening is likely to occur while it interacts with land. After that time, the system's close proximity to eastern Cuba and an expected increase in southwesterly shear are likely to inhibit significant re-strengthening. The latest NHC wind speed forecast has been lowered from the previous advisory at 72-120 h. Given the expected land interaction and less than ideal upper-level environment it is best to remain conservative at this time. Interests in Hispaniola, the Bahamas, Cuba, and Florida should continue to monitor forecasts as changes to both the track and intensity are likely. Key Messages: 1. Potential Tropical Cyclone Nine will produce heavy rains and potentially life-threatening flash flooding and mudslides across the northern Leeward Islands, the Virgin Islands, Puerto Rico, and the Dominican Republic. 2. Tropical storm conditions are likely across portions of the Leeward Islands, the Virgin Islands, and Puerto Rico today and will spread westward to portions of the Dominican Republic, Haiti, and the southeastern Bahamas and Turks and Caicos on Thursday and Thursday night. Tropical Storm Warnings are in effect for these areas. Do not focus on the details of the track forecast, as rainfall and wind hazards will extend far from the center of the system. 3. The details of the long-range track and intensity forecasts remain more uncertain than usual since the system does not have a well-defined center and it is expected to move near or over portions of the Greater Antilles later this week. However, this system could bring some rainfall and wind impacts to portions of Cuba, the central and northwest Bahamas, and Florida later this week and this weekend. Interests there should monitor its progress and updates to the forecast over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 15.8N 63.7W 40 KT 45 MPH...POTENTIAL TROP CYCLONE 12H 30/0000Z 16.9N 66.4W 45 KT 50 MPH...TROPICAL CYCLONE 24H 30/1200Z 18.5N 69.8W 50 KT 60 MPH 36H 31/0000Z 19.9N 73.0W 40 KT 45 MPH...INLAND 48H 31/1200Z 21.4N 76.0W 40 KT 45 MPH...NEAR COAST 60H 01/0000Z 22.7N 78.3W 40 KT 45 MPH...OVER WATER 72H 01/1200Z 23.8N 80.2W 45 KT 50 MPH 96H 02/1200Z 26.3N 82.6W 45 KT 50 MPH 120H 03/1200Z 29.0N 83.5W 45 KT 50 MPH $$ Forecaster Brown
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