|
Show Selection: |
| #1144929 (Received by flhurricane at: 10:54 PM 22.Jul.2023) TCDAT5 Hurricane Don Discussion Number 36 NWS National Hurricane Center Miami FL AL052023 1100 PM AST Sat Jul 22 2023 Don`s structure on satellite imagery remains well organized for a tropical cyclone at such a high latitude in late July. A small but distinct eye has persisted, surrounded by moderately cold cloud tops. However, the coldest cloud tops are beginning to erode on the north edge of the eye, and the upper-level outflow has also become more restricted in that direction. These factors likely indicate that Don is starting to feel the effects of nearby cooler waters and increased vertical wind shear that will ultimately lead to a swift decline in intensity. For now, the latest subjective Dvorak estimates were T4.0 (65 kt) from both SAB and TAFB, and objective intensity estimates currently range from 53 kt to 69 kt. It is worth noting that UW-CIMSS ADT estimates have been much lower, apparently due to that objective technique failing to pick up on the eye pattern seen on satellite today. Discounting that outlier, a blend of other subjective and objective data supports an initial intensity of 65 kt for this advisory. Don`s wind radii have also been adjusted some due to a helpful ASCAT-B pass at 2348 UTC. Now that Don is moving north of a warm eddy in the Gulf Stream, the cyclone should soon encounter much colder sea-surface temperatures along its track. Thus, steady weakening is expected to begin shortly. As Don quickly loses its deep convection, the cyclone is forecast to become post-tropical in 36 h, with the circulation expected to open up into a trough axis after 48 h. This forecast is in good agreement with the global and hurricane-regional model guidance. Don is now moving to the north-northeast a bit faster than before at 015/12 kt. A continued turn to the northeast with a bit more acceleration is anticipated overnight into tomorrow as Don is embedded within southwesterly steering flow between a subtropical ridge to its southeast and a deep-layer trough located over eastern Canada. This pattern should persist until Don dissipates, with the system continuing to recurve eastward over the next 48 h. The track guidance has shifted a bit faster than the prior cycle but still remains along a similar trajectory. Thus the NHC track forecast remains very close to the prior track, but just a little faster. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 41.4N 49.6W 65 KT 75 MPH 12H 23/1200Z 43.3N 48.5W 55 KT 65 MPH 24H 24/0000Z 45.5N 46.0W 45 KT 50 MPH 36H 24/1200Z 47.2N 42.1W 35 KT 40 MPH...POST-TROPICAL 48H 25/0000Z 48.1N 37.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 25/1200Z...DISSIPATED $$ Forecaster Papin |
