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| #1108161 (Received by flhurricane at: 5:05 AM 21.Sep.2022) TCDAT3 Tropical Storm Gaston Discussion Number 4 NWS National Hurricane Center Miami FL AL082022 900 AM GMT Wed Sep 21 2022 Gaston has continued to improve on satellite imagery overnight. Curved bands can be seen rotating fully around the southwestern side of the tropical cyclone with a warm spot occasionally apparent near where the center is. I was somewhat skeptical that this structure was indicative of a formative inner core, but a helpful GMI microwave pass at 0407 UTC revealed this was no illusion, with a nearly closed ring of convection on both 89 and 37 GHz channels. Subjective Dvorak classifications from SAB were T3.0/45-kt and TAFB T3.5/55-kt. Given the improvement in structure tonight, the winds have been increased to 55-kt this advisory. Gaston continues to move to the north-northeast at 025/16 kt. A turn north northeastward is expected later today followed by a more eastward motion by Thursday. By the latter part of this week, Gaston is forecast to come to near screeching halt to the west of the Azores in weak steering currents as a mid-level ridge builds northward, related to Fiona`s downstream diabatic induced ridging. 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. Based on the current structure, Gaston might be able to intensify a bit more today. However as Gaston slows down the westerly upper-level flow the storm is embedded will likely cause the structure to deteriorate, with both the GFS and ECMWF simulated satellite imagery suggesting the convection could de-couple from the storm in about 48-60 hours. Thus, the latest forecast shows weakening during this time period, and Gaston could become a post-tropical extratropical cyclone as soon as 72 hours. The latest NHC intensity forecast is a bit higher, owing to the initial intensity, but remains fairly close to the previous forecast after 60 hours. Interests in the Azores should continue to monitor the forecast for Gaston. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 37.5N 42.6W 55 KT 65 MPH 12H 21/1800Z 38.8N 40.6W 60 KT 70 MPH 24H 22/0600Z 40.1N 37.7W 60 KT 70 MPH 36H 22/1800Z 40.8N 34.7W 55 KT 65 MPH 48H 23/0600Z 40.9N 32.6W 50 KT 60 MPH 60H 23/1800Z 40.8N 31.4W 45 KT 50 MPH 72H 24/0600Z 41.3N 31.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 25/0600Z 42.6N 33.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 26/0600Z 44.3N 35.2W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin |
