000 WTNT45 KNHC 290839 TCDAT5 Hurricane Isaac Discussion Number 14 NWS National Hurricane Center Miami FL AL102024 900 AM GMT Sun Sep 29 2024 The strong deep-layer shear and sub-24C sea surface temperatures continue to disrupt Isaac's cloud pattern, although recent images show a small burst of deep convection developing near the surface center. The outer convective curve bands are diminishing and have dissipated in the east semicircle of the cyclone. Based on the latest Dvorak satellite intensity estimates and a UW-CIMSS SATCON analysis, the initial intensity is set at 70 kt. Decreasing oceanic surface temperatures and a sharp increase in west-southwesterly vertical shear support further weakening as an extratropical cyclone through day 5. Isaac could lose what remains of its organized deep convection later tonight and become a post-tropical cyclone, as suggested by the global model simulated/IR forecast. In any event, extratropical transition is anticipated by Monday evening due to baroclinic forcing from a middle-latitude trough and the proximity of a frontal boundary. Isaac's initial motion is estimated to be northeastward, or 045/11 kt as it continues to be steered by the mid-latitude southwesterly flow. A turn toward the north-northeast by the middle part of this week is forecast in response to a mid- to upper-level trough approaching the cyclone from the west-northwest. Around the 72 hr period, Isaac should turn northward while moving around the eastern periphery of a larger baroclinic low-pressure system. An adjustment slightly to the right of the previous track advisory is again needed beyond the 24 hr period to conform with the latest consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 42.6N 36.5W 70 KT 80 MPH 12H 29/1800Z 43.5N 34.9W 60 KT 70 MPH 24H 30/0600Z 44.5N 31.8W 50 KT 60 MPH...POST-TROPICAL 36H 30/1800Z 46.0N 28.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 01/0600Z 47.8N 26.3W 40 KT 45 MPH...POST-TROP/EXTRATROP 60H 01/1800Z 49.9N 25.2W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 02/0600Z 52.0N 24.6W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 03/0600Z 56.4N 20.8W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 04/0600Z 60.3N 16.8W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts
Originally Posted at:
NATIONAL HURRICANE CENTER and CENTRAL PACIFIC HURRICANE CENTER
At The NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
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