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| #872958 (Received by flhurricane at: 4:41 PM 25.Aug.2016) TCDAT2 TROPICAL STORM GASTON DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 500 PM AST THU AUG 25 2016 Strong southwesterly shear continues to take a toll on Gaston. The cloud pattern has become more assymetric with all of the deep core convection located north and east of the center. This was confirmed by a recent SSMIS microwave overpass that showed significant southwest to northeast tilt between the low- and mid-level centers. Objective Dvorak T-numbers have decreased and subjective intensity estimates from TAFB and SAB support an initial wind speed of 55 kt. A large upper-level low near 23N 54W that is moving southwestward is expected to continue to produce an unfavorable upper-level environment over Gaston for another 12 to 18 hours. Some additional weakening is possible tonight, but the official NHC forecast shows little change in strength through Friday. After that time, Gaston should be moving around the northern portion of the upper-low and into a more favarable upper-level wind pattern. This combined with warm SSTs and a moist atmosphere should allow Gaston to re-strengthen over the weekend and once again become a hurricane. The updated NHC intensity forecast is slightly above the previous advisory after 36 hours, and is in good agreement with the latest SHIPS guidance. The initial motion remains northwestward at 15 kt. Gaston should move northwestward during the next day or so around a mid-level ridge over the east-central Atlantic. In 36 to 48 hours, a ridge is forecast to build to the north of Gaston, which should cause the cyclone to turn west-northwestward. Early next week, the ridge is forecast to weaken and Gaston is expected to turn northward, then recurve into the mid-latitude westerlies in 4 to 5 days. The track guidance is in good agreement during the first 48 hours, but there is some spread as to what longitude recurvature begins. The ECMWF shows a slower motion near the end of the forecast period and a track along the eastern side of the guidance envelope, while the GFS and GFS ensemble mean are along the western edge. The NHC track foreast remains near the middle of the guidance envelope and is in closest agreement with UKMET, FSSE, and multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 21.6N 45.5W 55 KT 65 MPH 12H 26/0600Z 23.4N 47.1W 55 KT 65 MPH 24H 26/1800Z 25.5N 49.6W 55 KT 65 MPH 36H 27/0600Z 27.0N 52.3W 60 KT 70 MPH 48H 27/1800Z 28.1N 54.7W 70 KT 80 MPH 72H 28/1800Z 30.2N 57.0W 85 KT 100 MPH 96H 29/1800Z 31.8N 57.7W 95 KT 110 MPH 120H 30/1800Z 34.0N 55.0W 95 KT 110 MPH $$ Forecaster Brown |
