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| #1108661 (Received by flhurricane at: 4:50 AM 24.Sep.2022) TCDAT3 Tropical Storm Gaston Discussion Number 16 NWS National Hurricane Center Miami FL AL082022 900 AM GMT Sat Sep 24 2022 Since yesterday, Gaston has been transitioning to an asymmetric warm core post-tropical cyclone. A Friday morning 1227Z METOP-C scatterometer data confirmed that the transition had begun by depicting growing asymmetry in the wind field with a hundred-mile increase in gale-force winds in the northwest quadrant. Subsequent surface winds less than 60 miles from the center were 20 kt or less, all characteristics of a post-tropical/extratropical cyclone wind profile. The initial intensity is set at a generous 45 kt and is above the various subjective and objective satellite intensity estimates. As a result of increasing deep-layer shear and decreasing sea surface temperature beneath the cyclone, Gaston`s organized deep convection has diminished considerably. Only a few convective fragments remain well displaced to the southeast of the surface center. Accordingly, further weakening is expected, and Gaston should complete its post-tropical transition later today. A couple of the global models, however, indicate a mid-latitude shortwave trough/baroclinic zone interacting with post-tropical Gaston early Sunday morning, which could create a flare-up of deep convection, but this should be a short-lived event. Gaston`s initial motion is estimated to be west-southwestward, or 250/8 kt. Building high pressure over the northeast Atlantic should continue to steer the post-tropical cyclone westward through Monday morning, and west-southwestward until dissipation occurs toward the end of the week. The official track forecast is a little faster than the previous advisory and is nudged to the south beyond 48 hours to agree more with the NOAA HFIP HCCA model. Key Messages: 1. Tropical storm conditions over the western and central Azores today should diminish this evening as Gaston moves away from the islands. 2. Gaston is expected to produce heavy rainfall over the western and central Azores through Saturday. This rainfall may result in landslides and areas of flooding. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 38.6N 30.2W 45 KT 50 MPH 12H 24/1800Z 38.3N 31.5W 45 KT 50 MPH...POST-TROPICAL 24H 25/0600Z 38.7N 34.0W 40 KT 45 MPH...POST-TROPICAL 36H 25/1800Z 38.7N 36.4W 35 KT 40 MPH...POST-TROPICAL 48H 26/0600Z 38.1N 38.2W 35 KT 40 MPH...POST-TROPICAL 60H 26/1800Z 37.4N 39.9W 35 KT 40 MPH...POST-TROPICAL 72H 27/0600Z 36.6N 41.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 28/0600Z 33.9N 47.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 29/0600Z...DISSIPATED $$ Forecaster Roberts |
