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| #1108881 (Received by flhurricane at: 10:45 AM 25.Sep.2022) TCDAT3 Tropical Storm Gaston Discussion Number 21 NWS National Hurricane Center Miami FL AL082022 300 PM GMT Sun Sep 25 2022 The large convective burst that fired overnight and this morning appears to have lead to Gaston`s center reforming under the deep convection further to the north and west. This also evident in GOES-16 GLM lightning data that showed a clear arcing pattern embedded in the convection prior to the new center becoming evident on visible satellite imagery. Since then, the convection has been rapidly decaying, as the storm loses instability support from a sharp upper-level trough as it moves into its axis. Subjective and objective Dvorak numbers this morning were still CI 3.0/45-kt from TAFB and UW-CIMSS ADT. While scatterometer data largely missed the circulation earlier, it still showed tropical storm force winds extending well to the northeast of the center. The initial intensity is being maintained at 45 kt for this advisory. Gaston, post reformation, has made its westward turn, with the latest motion estimate at 270/10 kt. Gaston is currently situated between an anomalously strong deep-layer ridge to its northeast, and a more climatological ridge to its southwest. These features are forecast to merge over the next 24-48 hours to the northwest of Gaston, and should help steer the storm more to the west-southwest for the remainder of its lifespan. The guidance this cycle is just a bit further south and west compared to the previous cycle, and the latest NHC track forecast was nudged in that direction, following the consensus aids TVCN and HCCA. Gaston might have had its last convective hurrah this morning, with the GFS, ECMWF, CMC, and HWRF suggesting the storm will struggle to produce organized convection from here on out. This could be related to the upper-level flow pattern, where the storm is moving out of an environment favorable for ascent into an environment favorable for descent, limiting convection, especially as it continues to traverse 24-25C SSTs. The latest forecast still shows Gaston becoming a post-tropical cyclone in about 24 hours, but if the convection does not return before then, this evolution could occur sooner. The low should persist another day or two before it opens up into a trough in the subtropical Atlantic in about 72 hours, in agreement with the majority of the global model guidance. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 39.4N 36.5W 45 KT 50 MPH 12H 26/0000Z 39.2N 38.0W 40 KT 45 MPH 24H 26/1200Z 38.7N 39.9W 35 KT 40 MPH...POST-TROPICAL 36H 27/0000Z 38.0N 41.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 27/1200Z 37.4N 44.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 28/0000Z 36.8N 47.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 28/1200Z...DISSIPATED $$ Forecaster Papin |
