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| #892585 (Received by flhurricane at: 10:49 PM 18.Jun.2017) TCDAT2 Potential Tropical Cyclone Two Discussion Number 2 NWS National Hurricane Center Miami FL AL022017 1100 PM AST Sun Jun 18 2017 The convective cloud pattern associated with the disturbance has continued to improve since the previous advisory, with a curved convective band now wrapping more than halfway around the alleged center. As a result, the initial intensity has been increased to 35 kt, consistent with a TAFB Dvorak estimate of T2.5/35 kt. The overall environment is expected to be conducive for some additional development for the next 24-36 hours before southwesterly vertical wind shear increases to more than 20 kt by 48 hours and beyond across the eastern Caribbean Sea. The disturbance is expected to be a tropical storm before reaching the Windward Islands in 36 hours or so. The system is forecast to become a remnant low by 72 hours and dissipate by day 4 due to quite hostile upper-level winds. The official intensity forecast is similar to the previous advisory and closely follows the consensus model IVCN. An Air Force Reserve reconnaissance aircraft is scheduled to investigate the disturbance Monday afternoon. The National Hurricane Center now has the option to issue advisories on disturbances that are not yet tropical cyclones, but which pose the threat of bringing tropical storm or hurricane conditions to land areas within 48 hours. Under previous policy this was not possible. These systems are known as Potential Tropical Cyclones in advisory products and are numbered from the same list as depressions. Because of the threat to the Windward Islands, advisories have been initiated on Potential Tropical Cyclone Two and the appropriate warnings have been issued by the respective governments in the Windward Islands. Advisory packages will continue until the threat of tropical-storm-force winds for land areas sufficiently diminishes, although if the system becomes a tropical cyclone, the normal rules for discontinuing advisories would apply. Users should be aware that forecast uncertainty for disturbances is generally larger than for tropical cyclones, especially beyond 48-72 hours. The initial motion estimate remains 280/20 kt. The disturbance is expected to be steered westward to west-northwestward at around 20 kt for the next couple of days along the southern periphery of a strong deep-layer ridge located across most of the subtropical and tropical Atlantic. The new NHC track forecast is close to the previous advisory and the consensus model TVCN through 48 hours, and then lies a little south of the previous track at 72 hours due to expected weakening and decoupling of the low- and upper-level circulations. Given that tropical storm conditions are expected to extend well north of the center, users should not focus on the exact track of the center, and the track forecast is of lower certainty than usual. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 7.9N 52.4W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 12H 19/1200Z 8.7N 55.2W 40 KT 45 MPH...TROPICAL CYCLONE 24H 20/0000Z 9.9N 58.8W 45 KT 50 MPH 36H 20/1200Z 11.1N 62.3W 45 KT 50 MPH 48H 21/0000Z 12.1N 65.9W 40 KT 45 MPH 72H 22/0000Z 13.5N 73.4W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 23/0000Z...DISSIPATED $$ Forecaster Stewart |
