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| #1240577 (Received by flhurricane at: 4:36 PM 06.Aug.2025) TCDAT4 Tropical Storm Dexter Discussion Number 12 NWS National Hurricane Center Miami FL AL042025 500 PM AST Wed Aug 06 2025 Similar to the past couple of days, the high vertical wind shear over Dexter caused its low-level circulation to become exposed to the west of the the deep convection earlier this afternoon. A scatterometer pass received after the prior advisory also suggested that Dexter's vortex is becoming more elongated, with signs of a baroclinic zone starting to take shape to the northeast of the center. These signatures suggest that Dexter may soon undergo extratropical transition. The earlier scatterometer pass had a peak wind retrieval of 43 kt, and that value, combined with similar subjective and objective intensity estimates, support maintaining 45 kt this advisory. Dexter continues to gradually accelerate to the east-northeast, with the estimated motion now at 070/14 kt. The storm remains well embedded in the mid-latitude westerly flow as a shortwave trough drops southward towards Dexter. The subsequent trough interaction is forecast to keep Dexter moving quickly east-northeastward with just a subtle bend northeastward from 24-48 h. Compared to 24 h ago, the track guidance is in much better agreement with less along-track spread, and the latest NHC track forecast is very similar to the prior advisory, near the simple and corrected consensus aids. With vertical wind shear now around 40 kt and the cyclone also crossing the north edge of the Gulf Stream, most of the subsequent strengthening shown in the intensity forecast will be due to baroclinic processes as Dexter undergoes extratropical transition. The global and regional hurricane model fields shows Dexter's metamorphosis, with to development of frontal features as the wind field becomes quite asymmetric. In fact, the maximum sustained winds in 24-36 h are likely related to a sting jet that curves cyclonically around the cyclone's western flank during this time frame. The hurricane-regional models, and even the most recent 12 UTC ECMWF run show winds up to hurricane-force in the southwest quadrant. Thus, the latest NHC intensity forecast will now explicitly show a 65-kt extratropical cyclone in 36 h. After occlusion, the low will slowly weaken through the remainder of the forecast period, ultimately dissipating by early next week in the far northeastern Atlantic. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 40.0N 56.3W 45 KT 50 MPH 12H 07/0600Z 40.6N 53.5W 50 KT 60 MPH 24H 07/1800Z 41.9N 49.3W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 08/0600Z 43.5N 45.3W 65 KT 75 MPH...POST-TROP/EXTRATROP 48H 08/1800Z 44.8N 41.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 09/0600Z 45.5N 37.1W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 09/1800Z 46.0N 32.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 10/1800Z 47.0N 24.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 11/1800Z...DISSIPATED $$ Forecaster Papin |
