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| #1144180 (Received by flhurricane at: 10:57 PM 17.Jul.2023) TCDAT5 Tropical Storm Don Discussion Number 16 NWS National Hurricane Center Miami FL AL052023 300 AM GMT Tue Jul 18 2023 The convective structure of Don this evening has improved somewhat, with a decent area of -55 to -65C cold cloud tops centered a bit to the northeast of the low-level center. The center is also perhaps a bit better defined than earlier, with the ongoing convective activity possibly helping to tighten the center up. While subjective Dvorak classifications have not increased much this evening, an ASCAT-C pass at 2302 UTC caught the eastern portion of the circulation, with several believable wind vectors of up to 35 kt. Thus, Don is being upgraded to a tropical storm this advisory with sustained winds of 35 kt. Don continues to move southeastward at 125/11 kt. This motion is expected to continue curving clockwise over the next several days as the cyclone remains steered by a building mid-level ridge that is forecast to shift southwestward to northwestward relative to Don. Eventually this ridge will fold over the storm, allowing Don to begin gaining latitude again in 48-60 h. Overall, the track guidance this cycle has shifted a bit to the east and the NHC track has been shifted a little in that direction, though still remains much further west than the ECMWF model. There continues to be a large spread in guidance solutions by the end of the forecast period, and the current forecast remains low-confidence in that time frame. Even though Don is a bit stronger currently, the overall forecast environment is not all that conducive for much intensification in the short-term. Sea-surface temperatures under the cyclone are around 24C currently, and are only forecast to warm perhaps another degree C over the next 36-48 h. However, model-derived soundings from the GFS and HAFS models suggest that tropospheric instability does increase as environmental temperatures subtly cool in the mid-levels. The simulated IR imagery from these models around that time shows better organization of convective activity around a smaller core, and if this structure were to verify, some gradual intensification is possible. The latest NHC intensity forecast shows a bit more intensification than before, mostly related to the initial intensity, but still caps the system off as a 45-kt tropical storm by the end of the forecast period, which remains a bit under the model consensus. The latter part of the forecast is likely dependent on the Don`s ultimate track. A further left track, like the GFS and HAFS-A/B, may take the cyclone over warmer SSTs, and result in a stronger storm. However, a more rightward track like the ECMWF would take Don over its cold wake and likely would limit additional intensification. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 37.4N 40.4W 35 KT 40 MPH 12H 18/1200Z 36.3N 39.3W 35 KT 40 MPH 24H 19/0000Z 34.9N 39.0W 35 KT 40 MPH 36H 19/1200Z 34.1N 39.3W 35 KT 40 MPH 48H 20/0000Z 33.8N 40.4W 40 KT 45 MPH 60H 20/1200Z 34.2N 41.6W 40 KT 45 MPH 72H 21/0000Z 35.0N 43.2W 45 KT 50 MPH 96H 22/0000Z 37.4N 46.8W 45 KT 50 MPH 120H 23/0000Z 41.3N 49.2W 45 KT 50 MPH $$ Forecaster Papin |
