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