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| #1158922 (Received by flhurricane at: 10:46 PM 25.Oct.2023) TCDAT5 Hurricane Tammy Discussion Number 31 NWS National Hurricane Center Miami FL AL202023 1100 PM AST Wed Oct 25 2023 The extratropical transition of Tammy appears to be well underway. The eye is no longer apparent in satellite images, and deep convection has eroded over the western portion of the circulation. A dry slot has become evident between the small area of convection near Tammy`s center and a long, linear convective band well to its east and southeast. Based on the lower satellite intensity estimates this evening, the initial intensity is brought down to 80 kt for this advisory. If it hasn`t already, Tammy is expected to completely merge with a nearby front soon. In the near term, the increasing shear and drier air associated with a deep-layer trough to the west should result in a significant disruption of Tammy`s convection. However, Tammy will remain a powerful cyclone even after it becomes post-tropical, with an expanding outer wind field during this time. After the rapid warm seclusion process is completed, global model fields indicate Tammy could shed its frontal structure by 36 h. A reduction in wind shear is forecast soon thereafter, and convection could redevelop near Tammy`s center in 2-3 days while it moves over 25-26C waters. Though it is not explicitly forecast, there is some potential based on the GFS and ECMWF simulated satellite imagery that Tammy could reacquire tropical characteristics this weekend or early next week. The long-term motion of Tammy is 015 degrees/17 kt, but more recently the cyclone appears to be turning northward as expected. Over the next day or so, Tammy is forecast to slow down and move generally northwestward. From there, the global and regional models offer little clarity regarding the future track of Tammy, with extremely divergent solutions beyond about 36 h. The track differences appear to be related to the extent of Tammy`s interaction with a cutoff mid-level low that develops to the southwest of Tammy later this week. Several of the global models (ECMWF, UKMET, CMC) show this feature moving westward and remaining far enough away from Tammy that little interaction occurs. These models move Tammy generally eastward through early next week. The latest GFS and regional model runs show Tammy rotating around this mid-level feature and moving much farther west and southwest over the southwestern Atlantic. The spread between the 96-h GFS and ECMWF forecast positions is almost 1400 n mi, making the longer-term track forecast highly uncertain. Given this enormous spread, little change was made to the official forecast tonight. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 29.9N 57.8W 80 KT 90 MPH 12H 26/1200Z 30.7N 58.6W 70 KT 80 MPH...POST-TROP/EXTRATROP 24H 27/0000Z 31.3N 59.8W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 27/1200Z 31.6N 60.8W 60 KT 70 MPH...POST-TROPICAL 48H 28/0000Z 31.9N 62.0W 55 KT 65 MPH...POST-TROPICAL 60H 28/1200Z 32.1N 61.7W 55 KT 65 MPH...POST-TROPICAL 72H 29/0000Z 32.2N 61.0W 50 KT 60 MPH...POST-TROPICAL 96H 30/0000Z 32.4N 60.1W 40 KT 45 MPH...POST-TROPICAL 120H 31/0000Z 32.5N 59.0W 35 KT 40 MPH...POST-TROPICAL $$ Forecaster Reinhart |
