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| #1240543 (Received by flhurricane at: 10:51 AM 06.Aug.2025) TCDAT4 Tropical Storm Dexter Discussion Number 11 NWS National Hurricane Center Miami FL AL042025 1100 AM AST Wed Aug 06 2025 This morning, Dexter's structure continues to be quite resilient against an estimated 35-40 kt of westerly vertical wind shear over the storm. Deep convection continues to burst, still primarily down-shear, but an earlier AMSR2 microwave pass showed a bit more banding-type structure on the 37 GHz channel. Subjective Dvorak estimates from TAFB and SAB are now both T3.0/45 kt, and there were a few GOES-19 derived motion wind vectors up to 52 kt near 850 mb on the west side of Dexter's low-level circulation. These data support raising the initial intensity to 45 kt for this advisory. Dexter remains on an east-northeastward heading, a bit faster than earlier at 060/13 kt. The tropical storm is being steered by the mid-latitude westerly flow on the downstream side of a southward digging shortwave trough moving out of Atlantic Canada. The guidance has finally come into good agreement on this trough capturing Dexter in 36 h, leading to further acceleration east-northeastward until the trough and Dexter fully phase. The track guidance this cycle is a touch faster than earlier, and the latest NHC track forecast was nudged a little faster compared to the prior forecast cycle. Dexter's recent intensification is likely not fully tropical in nature. In fact, Dexter is currently positioned in the right entrance region of a 120 kt upper-level jet streak, which is likely providing some enhanced upper-level divergence and aiding the deep convection over the cyclone. The digging shortwave trough will also start impinging on the cyclone, initiating extratropical transition. This process should be complete in about 36 h, when both the GFS and ECMWF models show deep convection separating from Dexter's core. However, this will be a dynamic extratropical transition, with all the various hurricane-regional models suggesting the development of a sting jet, or branch of rapidly descending dry air, curving cyclonically around the cyclone's western flank. The NHC intensity forecast shows Dexter peaking as a 60-kt extratropical cyclone in about 36 h in response to this feature, and both HAFS-A/B suggest this intensity could be conservative. After the extratropical cyclone occludes, the winds should decrease again as it loses its baroclinic forcing, with the low opening up to a trough by the end of the forecast period over the far northeastern Atlantic. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 39.9N 58.2W 45 KT 50 MPH 12H 07/0000Z 40.4N 55.4W 50 KT 60 MPH 24H 07/1200Z 41.5N 51.4W 55 KT 65 MPH 36H 08/0000Z 42.9N 47.3W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 08/1200Z 44.4N 43.6W 55 KT 65 MPH...POST-TROP/EXTRATROP 60H 09/0000Z 45.2N 39.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 09/1200Z 45.6N 34.8W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 10/1200Z 47.0N 26.2W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 11/1200Z...DISSIPATED $$ Forecaster Papin |
