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| #1200158 (Received by flhurricane at: 11:12 PM 25.Sep.2024) TCDAT5 Tropical Storm Isaac Discussion Number 1 NWS National Hurricane Center Miami FL AL102024 1100 PM AST Wed Sep 25 2024 The non-tropical area of low pressure we have been monitoring to the northeast of Bermuda over the last day or so has become significantly better organized today, with deep central convection forming and now wrapping around a small surface circulation. While the system had previously been attached to an occluded frontal boundary to its northwest, recently received scatterometer data now shows that the circulation has fully detached form this boundary, and is producing winds of 40-45 kt in a small circular area embedded within the organizing convection. These structural changes indicate the the system has undergone and has completed tropical transition. Thus, the system is now being designated Tropical Storm Isaac this advisory, and the initial intensity is set to 45 kt based on the earlier scatterometer data. Isaac is moving just north of due east at 85/10 kt. This motion should continue with a gentle turn more east-northeastward over the next several days as the system is steered primarily by mid-level ridging present to its south. However, there does not appear to be a mid-latitude trough early on to help the storm to accelerate much over the next few days. The initial NHC track forecast is in good agreement with the simple and corrected consensus aids TCVN and HCCA. While Isaac is traversing only marginally warm waters, it is also still embedded within the base of an upper-level trough which has reduced tropospheric stability due to colder upper-level temperatures. This is partially why Isaac has been able to develop organized deep convection this evening. The shear is not anticipated to increase much over the next couple of days, which could allow for some gradual intensification. The NHC intensity forecast is in good agreement the with HCCA and ECMWF forecasts and shows a peak intensity of 60 kt in 48 h, followed by gradual weakening after 72 h as sea-surface temperatures cool further and shear begins to increase more markedly. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 37.1N 54.1W 45 KT 50 MPH 12H 26/1200Z 37.1N 52.3W 50 KT 60 MPH 24H 27/0000Z 37.3N 49.8W 50 KT 60 MPH 36H 27/1200Z 37.9N 46.8W 55 KT 65 MPH 48H 28/0000Z 38.8N 43.2W 60 KT 70 MPH 60H 28/1200Z 40.1N 39.5W 60 KT 70 MPH 72H 29/0000Z 41.4N 35.8W 60 KT 70 MPH 96H 30/0000Z 42.7N 29.4W 55 KT 65 MPH 120H 01/0000Z 42.5N 21.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin |
