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| #1200979 (Received by flhurricane at: 4:39 PM 29.Sep.2024) TCDAT5 Tropical Storm Isaac Discussion Number 16 NWS National Hurricane Center Miami FL AL102024 900 PM GMT Sun Sep 29 2024 The increasingly hostile sea surface temperatures, strong vertical wind shear, and dry air wrapping around the southern half of Isaac has weakened the cyclone. The last few visible stallite images before sundown suggest that the vortex could be tilted, with the low-level center displaced southwest of the upper-level vortex. Additionally, deep convection has become less symmetric since the last advisory, with convection in the southern semicircle likely being cut off by the aformentioned dry air. This structure is indicative of a progressing extratropical transition, as Isaac continues to interact with a baroclinic frontal zone to its northeast. The initial intensity is set to 60 kt for this advisory, which is a blend of the subjective and objective satellite classifications. Tropical Storm Isaac is forecast to continue its extratropical transition and become a fully extratropical cyclone on Monday. This is in agreement with model-diagnosed thermodynamics that maintain a warm core until this time, in addition to simulated IR satellite data from the GFS and ECMWF models. The intensity forecast is similar to the previous forecast and shows a steady decrease in maximum sustained winds through the forecast period. The forward motion of the cyclone continues to be northeastward (050/10 kt). This general motion is forecast to continue for the next day or so as Isaac continues to be steered by a mid-level trough to its west. This mid-level trough will steer Isaac towards the north-northeast beyond 36 hr. Beyond 96 hr, global model data indicates Isaac will be absorbed by a more potent extratropical cyclone just southeast of Iceland. The track forecast is again adjusted eastward from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 43.8N 34.7W 60 KT 70 MPH 12H 30/0600Z 44.6N 32.4W 55 KT 65 MPH 24H 30/1800Z 45.8N 28.6W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 01/0600Z 47.4N 25.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 01/1800Z 49.3N 24.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 60H 02/0600Z 51.4N 23.2W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 02/1800Z 53.1N 22.3W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 03/1800Z 57.9N 17.9W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 04/1800Z...DISSIPATED $$ Forecaster Mahoney/Blake |
