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| #872834 (Received by flhurricane at: 4:41 AM 24.Aug.2016) TCDAT2 TROPICAL STORM GASTON DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 500 AM AST WED AUG 24 2016 A 0414 UTC AMSR2 microwave image revealed that Gaston's structure has improved with the development of a well-defined low-level cloud ring and a mid-level microwave eye. However, the mid-level center is displaced about 25 n mi to the northeast of the low-level center. Dvorak intensity estimates from TAFB and SAB are both T4.0/65 kt, but objective numbers are still between 55-60 kt. Given the tilted structure of the cyclone, the initial intensity is only raised to 60 kt on this advisory. University of Wisconsin CIMSS shear analyses indicate that 10 kt of southwesterly shear is affecting Gaston, which could explain the cyclone's tilted structure. The shear is expected to remain low enough during the next 24 hours to allow Gaston to strengthen to a hurricane later today. However, the intensification trend should be interrupted after 24 hours, continuing through day 3, when Gaston moves into a higher shear zone to the east of a mid-/upper-level low. Some strengthening is then probable on days 4 and 5 when Gaston moves north of the upper low into a lower-shear environment. The intensity models are in very good agreement on this general scenario, and the official NHC forecast was only lowered a bit at 36 and 48 hours to be more in line with the IVCN consensus. Tracking the low-level center observed in microwave data yields a motion of 290/15 kt. Gaston is approaching a break in the subtropical ridge caused by the aforementioned mid-/upper-level low, and the steering currents should cause the motion to become northwestward later today and continue along that heading for the next four days. By day 5, Gaston is expected to slow down and turn northward to the west of a mid-level high. There is lower-than- normal spread among the track guidance for the entire five-day forecast period, and the NHC forecast continues to closely follow the TVCN multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 14.9N 38.6W 60 KT 70 MPH 12H 24/1800Z 16.2N 40.6W 65 KT 75 MPH 24H 25/0600Z 18.2N 42.9W 70 KT 80 MPH 36H 25/1800Z 20.4N 45.1W 70 KT 80 MPH 48H 26/0600Z 22.9N 47.2W 70 KT 80 MPH 72H 27/0600Z 26.9N 52.3W 70 KT 80 MPH 96H 28/0600Z 29.5N 55.5W 80 KT 90 MPH 120H 29/0600Z 31.5N 55.5W 85 KT 100 MPH $$ Forecaster Berg |
