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| #1200457 (Received by flhurricane at: 10:51 PM 26.Sep.2024) TCDAT5 Tropical Storm Isaac Discussion Number 5 NWS National Hurricane Center Miami FL AL102024 1100 PM AST Thu Sep 26 2024 Isaac`s structure has quickly improved this evening on satellite imagery. Deeper cold convection down to -60 C has been fully wrapping around the center, and the last few frames show a warm spot, which could very well be a formative eye. While the subjective Dvorak classifications hasn`t changed much this evening, the objective estimates, especially DPRINT and DMINT from UW-CIMSS have increased to 54 and 51 kt respectively. Similar to last night, a late arriving set of scatterometer passes showed a tight vortex with derived-winds up to 49 kt. Assuming some undersampling of the small circulation, the initial intensity is raised to 55 kt this advisory. Isaac appears to have made a wobble south of due east earlier this evening, but more recently has resumed an eastward motion at 90/10 kt. This motion with a gradual turn to the east-northeast should occur over the next couple of days. Afterwards, the forward motion of Isaac is likely to become very critical to its future track trajectory. The poleward shift in the guidance that started earlier today has continued, possibly due to the slower forecasted forward motion of the storm, making it more likely to be captured by an upstream mid-latitude trough digging in from the west. The latest NHC track forecast has continued the northward shift started on the prior cycle, but is still not as far north and east as the bulk of the guidance suite, and further adjustments in that direction may be needed in future forecasts. Given the improvement in Isaac`s structure this evening, it`s looking increasingly likely the storm will soon become a hurricane. Vertical wind shear remains under 20 kt while sea-surface temperatures (SSTs) between 26-27 C for the next 24 h should allow additional intensification. After that time, shear begins to increase more as SSTs also begin to cool. These factors are expected to result in a leveling off in intensity, though cold upper-level temperatures should maintain enough instability to keep moderate to deep convection near the system. By 72 h, weakening should begin, with extratropical transition likely to be underway, finishing sometime early next week over the high-latitudes of the North Atlantic. The latest NHC intensity forecast is above much of the guidance in the short-term due to recent satellite trends, but falls back towards the reliable HCCA consensus aid after 24 hours. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 37.1N 49.8W 55 KT 65 MPH 12H 27/1200Z 37.1N 47.6W 65 KT 75 MPH 24H 28/0000Z 38.1N 44.1W 70 KT 80 MPH 36H 28/1200Z 39.5N 40.5W 70 KT 80 MPH 48H 29/0000Z 41.1N 37.9W 65 KT 75 MPH 60H 29/1200Z 42.6N 36.4W 65 KT 75 MPH 72H 30/0000Z 43.7N 35.1W 60 KT 70 MPH 96H 01/0000Z 46.0N 30.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 02/0000Z 50.0N 26.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin |
