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| #872856 (Received by flhurricane at: 10:47 AM 24.Aug.2016) TCDAT2 TROPICAL STORM GASTON DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 1100 AM AST WED AUG 24 2016 Gaston's overall cloud pattern has not changed much in organization since the last advisory. The low-level center is located underneath a small central dense overcast (CDO), with hints of a prototype eye within the convective mass. A solid band, attached to the CDO, wraps around the eastern half of the circulation. A 1234 UTC ASCAT pass supports keeping the initial wind estimate at 60 kt. Gaston could still reach hurricane strength today. However, the shear associated with a potent mid- to upper-level trough along 52W is forecast to greatly increase over Gaston and peak in 36 to 48 hours. Even though the cyclone will gradually be moving over warmer waters at that time, the shear should be enough to arrest its development or perhaps even result in weakening. By 72 hours, Gaston's involvement with the trough should lessen and the shear should decrease. Much lower westerly shear is forecast toward the end of the forecast period, which should give Gaston an opportunity to re-strengthen, and perhaps significantly, as it moves over waters of around 29 deg C. The new NHC intensity forecast is reduced some compared to the previous one through 48 hours, but shows slightly greater intensification by 120 hours. The official forecast is in generally in good agreement with the multi-model consensus. The latest fixes indicate that Gaston's heading has a much greater northerly component, and the long-term initial motion estimate is 305/14. Gaston is expected to move northwestward between a subtropical ridge over the eastern Atlantic and the aforementioned trough to the west during the next 3 days. After 72 hours, Gaston should gradually turn north-northwestward and northward with a considerable decrease in forward speed, when it encounters a more substantial break in the Atlantic subtropical ridge along 60W. The ECMWF shows less ridging and makes Gaston vulnerable to the mid- latitude westerlies earlier, with the model showing recurvature before 120 hours. The bulk of the guidance, however, lies farther west, with these models showing more ridging north of Gaston through day 5. The new track forecast is a little right of the previous one through 72 hours in response to the cyclone's abrupt change in heading since the last advisory and is close to a blend of the ECMWF and GFS solutions. The track beyond 72 hours was adjusted westward and remains close to a ECMWF/GFS model blend. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 16.1N 39.4W 55 KT 65 MPH 12H 25/0000Z 17.5N 41.2W 65 KT 75 MPH 24H 25/1200Z 19.6N 43.5W 60 KT 70 MPH 36H 26/0000Z 21.9N 45.6W 55 KT 65 MPH 48H 26/1200Z 24.3N 47.9W 55 KT 65 MPH 72H 27/1200Z 27.8N 53.1W 65 KT 75 MPH 96H 28/1200Z 30.5N 55.9W 80 KT 90 MPH 120H 29/1200Z 32.2N 56.5W 90 KT 105 MPH $$ Forecaster Kimberlain |
