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| #1143997 (Received by flhurricane at: 4:57 PM 16.Jul.2023) TCDAT5 Subtropical Depression Don Discussion Number 11 NWS National Hurricane Center Miami FL AL052023 500 PM AST Sun Jul 16 2023 Don is a strange system. Satellite images show that convection has increased in aerial coverage in the southeastern quadrant of the cyclone, although it is still not well defined in banding features or other organizational metrics. The convection is also closer to the center, and the upper-level low near Don has weakened. In some ways it has actually gained some tropical characteristics since yesterday despite remaining over cool waters, but the convective organization is still shy of a tropical cyclone. Regardless of the scientific curiosity, there are no signs that the winds have strengthened, and Don is best classified as a 30-kt subtropical depression on this advisory. Don has turned to the east this afternoon and should gradually execute a large clockwise loop over the central Atlantic during the next few days, first turning southeast, then south and southwest through Wednesday. The only change to that part of the forecast was a slight eastward adjustment at a faster forward speed. There continues to be a large guidance spread on days 4/5 as Don moves south of a blocking ridge and eventually turns to the west or northwest. Interestingly, the regional hurricane models are generally on the left side of the guidance envelope, and the global models are on the right side. I just don`t trust the regional guidance in this set-up where the large-scale steering might matter more than the storm structure (and the regional models struggle in hybrid situations). Thus, the forecast leans on the eastern side of the guidance at long range, resulting in little change from the previous forecast, east of the model consensus. Don isn`t likely to change much in intensity for the next few days, with a somewhat unfavorable environment persisting. While not explicitly shown, it could degenerate into a remnant low during the next few days until it reaches warmer waters. Then, a fair bit of the guidance brings the system back (as a tropical cyclone) due to more instability over warmer waters in a lighter shear environment. The forecast does show Don as a tropical storm in 4 days, but with water temperatures still below 25C, it isn`t expected to be very strong at long range. The new NHC forecast is close to the previous one and remains lower than the guidance at the extended time ranges. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 39.3N 47.0W 30 KT 35 MPH 12H 17/0600Z 39.4N 45.3W 30 KT 35 MPH 24H 17/1800Z 38.5N 42.9W 30 KT 35 MPH 36H 18/0600Z 37.0N 41.1W 30 KT 35 MPH 48H 18/1800Z 35.3N 40.6W 30 KT 35 MPH 60H 19/0600Z 33.8N 40.9W 30 KT 35 MPH 72H 19/1800Z 33.0N 41.5W 30 KT 35 MPH 96H 20/1800Z 33.4N 44.3W 35 KT 40 MPH...TROPICAL CYCLONE 120H 21/1800Z 35.5N 48.0W 35 KT 40 MPH $$ Forecaster Blake |
