000 WTNT43 KNHC 210257 TCDAT3 Tropical Storm Gaston Discussion Number 3 NWS National Hurricane Center Miami FL AL082022 300 AM GMT Wed Sep 21 2022 The satellite presentation of Gaston has improved slightly since the previous advisory, with deep convection persisting over the low-level circulation center. The latest current intensity estimates reflect what has been seen in the satellite imagery, with TAFB and SAB coming in at 45 knots, while the ADT and AiDT values from UW-CIMSS showing 35 knots and 46 knots respectively. Based on a blend of these data along with the improved satellite appearance, the initial intensity has been raised to 45 knots. Gaston continues on a path toward the north-northeast, with the initial motion estimated to be 020/16 kt. A turn to northeast is expected today, followed by a turn to the east by Thursday as the tropical storm moves along the the northern periphery of a subtropical ridge. By late this week, Gaston is expected to stall to the west of the Azores in weak steering currents as a mid-level ridge builds to the north of cyclone. A turn to the northwest or north is expected over the weekend as Gaston moves in the steering flow between Hurricane Fiona to the west and the building mid-level ridge to the east. The latest NHC track forecast has changed little and lies very close to the previous advisory track, and closely follows the consensus track guidance. The period for additional intensification is quickly closing, as Gaston is moving over the 26C isotherm, and will move over progressively cooler water through the remainder of the forecast period. Additionally, the impact of the vertical wind shear will increase in a couple days as the tropical cyclone stalls out while westerly shear holds in the 25 to 30 knot range. As a result, the intensity forecast calls for slight strengthening today, followed by little change in strength for another day or so after that. The combination of cool SSTs, dry mid-level air, and increasing vertical wind shear should then lead to slow weakening through the remainder of the week. The latest NHC was adjusted upward through the first 24 hours to account for the strengthening which has already occurred, with only minor adjustments made through the remainder of the forecast period, closely following the consensus intensity aids. Interests in the Azores should continue to monitor the forecast for Gaston. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 36.2N 43.6W 45 KT 50 MPH 12H 21/1200Z 37.8N 41.9W 50 KT 60 MPH 24H 22/0000Z 39.3N 39.1W 50 KT 60 MPH 36H 22/1200Z 40.2N 36.0W 50 KT 60 MPH 48H 23/0000Z 40.4N 32.9W 45 KT 50 MPH 60H 23/1200Z 40.4N 31.9W 45 KT 50 MPH 72H 24/0000Z 40.4N 31.9W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 25/0000Z 41.5N 33.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 26/0000Z 43.5N 35.2W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster D. Zelinsky/Jelsema