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| #1144466 (Received by flhurricane at: 10:50 PM 19.Jul.2023) TCDAT5 Tropical Storm Don Discussion Number 24 NWS National Hurricane Center Miami FL AL052023 300 AM GMT Thu Jul 20 2023 Don continues to maintain a compact area of deep convection, with cold cloud tops between -60 to -65C attempting to rotate cyclonically into the northern semicircle of the storm`s circulation. An earlier ASCAT-B pass clipped Don`s east side with a peak wind-retrieval of 39 kt, but this pass might have missed higher winds closer to the center. In fact, a Synthetic Aperture Radar (SAR) pass that became available after the prior advisory suggests Don`s radius of maximum wind has contracted to near 20 n mi with a peak value of 49 kt, but this derived wind may have been contaminated by ice-scattering noted in microwave imagery. The most recent subjective Dvorak intensity estimate was T3.0/45-kt from TAFB, and the most recent objective intensity estimate from SATCON was 46 kt. A blend of these various data sources supports increasing Don`s intensity to 45 kt this advisory. There is still a window for Don to intensify more over the next 24 h while it remains over 25-26 C sea-surface temperatures (SSTs) and low shear helps ongoing convection moisten up the nearby environment in a compact area. Beyond that time, SSTs decrease markedly along Don`s track, related to the storm crossing its own cold wake. In addition, both the GFS- and ECMWF-based SHIPS guidance show environmental mid-level relative humidity dropping below 40 percent, and Don`s small core could become sensitive to any increase in shear, which could introduce drier air from the northeast. The most recent regional hurricane model simulations illustrate this possible scenario, with convection becoming sheared off to the southwest as dry air infiltrates the storm`s core in 48-60 h. Thus, the NHC intensity forecast continues to show a peak intensity of 50 kt, with Don beginning to weaken after 48 h. This NHC forecast is near the latest ICVN and HCCA consensus aids. The hurricane-regional guidance also suggests Don should become devoid of convection when it moves north of the Gulf Stream by 96 h, and the latest forecast now shows the system becoming post-tropical at that time. The tropical storm continues to move westward tonight, estimated at 270/5 kt. Don should soon begin to gain latitude again as a prominent mid-level ridge becomes centered to its northeast. As mentioned in the previous discussion, the model trends have been for this blocking ridge to be slow to move completely out of Don`s way, and the storm is forecast to only slowly recurve into the higher latitudes as a result. The track guidance this cycle has shifted a bit westward compared to the previous forecast, notably with the 18z ECMWF coming in farther west. The NHC track forecast has also been shifted a little westward, but not as far west as the TVCN and HCCA consensus aids, and further adjustments may be necessary in subsequent advisories. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 33.9N 40.9W 45 KT 50 MPH 12H 20/1200Z 34.0N 42.0W 50 KT 60 MPH 24H 21/0000Z 34.5N 43.6W 50 KT 60 MPH 36H 21/1200Z 35.3N 45.4W 50 KT 60 MPH 48H 22/0000Z 36.6N 47.1W 50 KT 60 MPH 60H 22/1200Z 38.3N 48.6W 45 KT 50 MPH 72H 23/0000Z 40.2N 49.3W 45 KT 50 MPH 96H 24/0000Z 43.9N 47.8W 40 KT 45 MPH...POST-TROPICAL 120H 25/0000Z 45.6N 42.5W 35 KT 40 MPH...POST-TROPICAL $$ Forecaster Papin |
