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| #1108479 (Received by flhurricane at: 5:03 AM 23.Sep.2022) TCDAT3 Tropical Storm Gaston Discussion Number 12 NWS National Hurricane Center Miami FL AL082022 900 AM GMT Fri Sep 23 2022 Gaston`s cloud pattern has changed considerably in appearance since yesterday. A tropical cyclone axisymmetric wind field that is typically concentrated about the surface center has transformed to a more asymmetric pattern with considerable expansion to the northeast due to the brisk mid-latitude westerlies and the sub-25C cool oceanic surface temperatures. Involvement between Gaston and a major shortwave trough/baroclinic zone noted in water vapor imagery and a recent AMSR2 microwave pass has resulted in a delta rain shield north of the exposed surface circulation. A subsequent polar jet finger is visible in imagery northeast of the center, with possible warm seclusion development. All these attributes may well be leading to post-tropical cyclone transition. The subjective satellite intensity estimates and a recent UW-CIMSS SATCON analysis yield an initial intensity of 50 kt for this advisory. Gaston is forecast to slowly weaken while the cyclone completes its post-tropical transition in about 36 hours or so. The official intensity forecast is similar to the previous one and is in line with the IVCN intensity consensus model. Gaston has begun its anticyclonic loop and is moving east-southeastward, or 115/8 kt. The cyclone is expected to turn toward the southeast today and southward along the southern periphery of mid-tropospheric ridge building to the north through Saturday morning while moving near the westernmost Azores. Afterward, Gaston should generally move toward the west-southwest and westward through the end of the period. The official forecast is nudged slightly to the north of the previous one in the short term, but closer after that, and is based on the various consensus aids. Key Messages: 1. Tropical storm conditions are occurring over portions of the western Azores, and will likely spread to the central Azores later today. 2. Gaston is expected to produce heavy rainfall over the western and central Azores today through Saturday. This rainfall may result in landslides and areas of flooding. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 40.5N 29.6W 50 KT 60 MPH 12H 23/1800Z 39.7N 28.9W 50 KT 60 MPH 24H 24/0600Z 38.6N 29.4W 50 KT 60 MPH 36H 24/1800Z 38.2N 31.2W 50 KT 60 MPH...POST-TROPICAL 48H 25/0600Z 38.6N 33.7W 50 KT 60 MPH...POST-TROPICAL 60H 25/1800Z 38.6N 36.1W 45 KT 50 MPH...POST-TROPICAL 72H 26/0600Z 38.6N 38.0W 40 KT 45 MPH...POST-TROPICAL 96H 27/0600Z 39.1N 41.0W 35 KT 40 MPH...POST-TROPICAL 120H 28/0600Z 38.2N 45.3W 30 KT 35 MPH...POST-TROPICAL $$ Forecaster Roberts |
