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| #1144040 (Received by flhurricane at: 10:48 PM 16.Jul.2023) TCDAT5 Subtropical Depression Don Discussion Number 12 NWS National Hurricane Center Miami FL AL052023 1100 PM AST Sun Jul 16 2023 Convection has been waxing and waning near Don this evening, with only a small area of -50 to -60C tops occuring to the east of the center. Despite the relatively meager convective structure, Don`s appearance now looks more akin to a sheared tropical depression, since the upper-level low that was over Don at the start of the weekend has largely dissipated. However, the most recent TAFB Dvorak classification kept the system subtropical given the limited convective activity, and so Don will still be classified as a subtropical cyclone at this time, with maximum sustained winds of 30 kt for this advisory. Don continues to move eastward, with the latest motion estimated at 090/9 kt. An anomalously strong low- to mid-level anticyclone is currently centered south of Don, and this feature is expected to shift westward and quickly build poleward to the west and northwest of the cyclone. Eventually this ridge will fold back over to Don`s north towards the end of this week. The net result of this pattern reconfiguration is Don should begin to execute a clockwise loop over the Central Atlantic, first turning southeast tomorrow, south and southwest by Tuesday, and finally turning westward and then northwestward towards the middle to latter part of the week. The track guidance this cycle has shifted back eastward, and only modest track adjustments were needed in the official forecast for the first three days, followed by an adjustment eastward in days 4-5. However, given the continued spread in the ensemble track guidance at that time range, that portion of the forecast remains low confidence. Don’s short-term future is dependent on its ability to continue producing enough convective activity to prevent it from becoming a remnant low. Right now, sea-surface temperatures over the system are around 23C, about the coldest they will be along its forecast track. As the system begins to lose latitude over the next several days, these waters warm to around 25C, while upper-level temperatures remain sufficently cold to result in increased instability. Both the regional-hurricane models and global models show Don maintaining or increasing convective activity near its center as it moves southward. For these reasons, the latest intensity forecast now shows the system transitioning to a tropical cyclone a bit earlier, and also shows some gradual intensification beginning at 48 hours as the system moves over these warmer waters. A bit more intensification is shown in the latter part of the forecast, but still remains under the majority of the guidance in the extended range given the larger-than-normal uncertainty in the location and structure of the system at the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 39.4N 45.8W 30 KT 35 MPH 12H 17/1200Z 39.1N 43.9W 30 KT 35 MPH 24H 18/0000Z 37.9N 41.8W 30 KT 35 MPH 36H 18/1200Z 36.3N 40.7W 30 KT 35 MPH...TROPICAL CYCLONE 48H 19/0000Z 34.6N 40.5W 35 KT 40 MPH 60H 19/1200Z 33.5N 40.9W 35 KT 40 MPH 72H 20/0000Z 33.2N 41.7W 40 KT 45 MPH 96H 21/0000Z 34.2N 44.6W 40 KT 45 MPH 120H 22/0000Z 37.2N 48.1W 40 KT 45 MPH $$ Forecaster Papin |
