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Chill falls over the Atlantic as the official season heads towards close
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| #873013 (Received by flhurricane at: 10:56 AM 26.Aug.2016) TCDAT2 TROPICAL STORM GASTON DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 1100 AM AST FRI AUG 26 2016 Gaston continues to be adversely impacted by about 20 kt of southwesterly vertical shear because of a strong upper low to the southwest. The shear is forcing the diminished deep convection to be primarily located north of the center. The TAFB and SAB current intensities indicated 55 kt at 12Z, which is supported by a 1330Z ASCAT-B scatterometer pass which just became available. As Gaston moves away from the upper-level low, the shear should drop fairly dramatically to between 5 and 10 kt by tomorrow. The shear should stay low through about 72 h while the cyclone traverses over quite warm waters. After about three days, Gaston should encounter strong mid-latitude upper-level westerlies and a return of hostile shear at the same time that SSTs steadily drop. The official NHC forecast is for steady intensification between days one and three, with gradual weakening thereafter. This forecast is based upon the IVCN intensity model consensus and is very similar to that from the previous advisory. Gaston's initial position is very well known, due to the center being along the edge of the deep convection. The tropical storm is moving toward the north-northwest at a rapid 15-kt clip, as it's being steered between the strong upper low and a subtropical ridge to its northeast. Around 72 h, Gaston should slow to a crawl as it reaches a weak steering pattern. But by the end of the forecast period, the system should be accelerating northeastward as it enters the mid-latitude westerlies. The track forecast is based upon the tightly clustered members of the TVCN track model consensus and is just slightly north of the previous advisory due to Gaston's initial position being more north than previously anticipated. The initial 34- and 50-kt wind radii were made slightly larger based upon an AMSU satellite pass and the wind radii forecast is similar to the RVCN consensus technique. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 25.2N 48.3W 55 KT 65 MPH 12H 27/0000Z 26.7N 50.1W 55 KT 65 MPH 24H 27/1200Z 27.9N 52.5W 65 KT 75 MPH 36H 28/0000Z 29.0N 54.3W 75 KT 85 MPH 48H 28/1200Z 29.9N 55.5W 85 KT 100 MPH 72H 29/1200Z 31.2N 56.1W 95 KT 110 MPH 96H 30/1200Z 32.5N 54.0W 90 KT 105 MPH 120H 31/1200Z 34.5N 50.0W 80 KT 90 MPH $$ Forecaster Landsea |
