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| #1144701 (Received by flhurricane at: 4:51 PM 21.Jul.2023) TCDAT5 Tropical Storm Don Discussion Number 31 NWS National Hurricane Center Miami FL AL052023 500 PM AST Fri Jul 21 2023 There has been a continued increase in banding in association with Don today. In visible satellite imagery, the primary convective band wraps nearly completely around the center, however the cloud tops have warmed over the northwestern portion of the storm recently. A late arriving ASCAT-C overpass that caught the northwestern portion of Don this morning revealed peak winds in the 43-45 kt range. Given the typical undersampling of that instrument and the fact that it missed the potentially stronger northeastern quadrant of the cyclone, the initial intensity has been increased to 50 kt, which is a little above the latest subject Dvorak wind speed estimates. Despite the slightly stronger initial intensity, the overall intensity forecast philosophy has not changed much. Don will be moving over the slightly warmer waters of the Gulf stream later tonight and Saturday which could result in some slight strengthening. The official forecast allows for this possibility and is close to the various intensity consensus aids through 24 hours. By early Sunday, Don is forecast to move north of the Gulf stream and over much colder SSTs, which should cause steady weakening. Simulated satellite imagery from the global models suggest that Don will struggle to produce deep convection by late Sunday, marking the system`s transition to a post-tropical cyclone. Dissipation is predicted just after 72 hours. The storm has made its anticipated northwestward turn. A mid-level ridge to the north-northeast of Don is expected to shift eastward during the next day or so and allow the cyclone to turn northward on Saturday. After that time, Don is forecast to turn northeastward within low- to mid-level southwesterly flow between the ridge and a broad trough over eastern Canada. The dynamical model envelope made a noticeable eastward shift at 36 hours and beyond, which required an eastward adjustment to the NHC track forecast. The new track lies along the western edge of the guidance envelope and is not as fast east as the multi-model consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 36.6N 47.5W 50 KT 60 MPH 12H 22/0600Z 37.9N 48.9W 55 KT 65 MPH 24H 22/1800Z 40.0N 50.2W 55 KT 65 MPH 36H 23/0600Z 42.4N 50.0W 50 KT 60 MPH 48H 23/1800Z 44.6N 48.6W 40 KT 45 MPH...POST-TROPICAL 60H 24/0600Z 47.1N 45.1W 35 KT 40 MPH...POST-TROPICAL 72H 24/1800Z 48.7N 41.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 25/1800Z...DISSIPATED $$ Forecaster Brown |
