Hurricane Isaac Discussion Number  13
NWS National Hurricane Center Miami FL       AL102024
300 AM GMT Sun Sep 29 2024

Isaac continues to weaken tonight. Southwesterly shear and 
intrusions of drier mid-level air have eroded convection over the 
southern portion of the hurricane, and there is no longer a coherent 
eye feature in satellite images. A partial scatterometer pass shows 
a frontal zone in close proximity to the east of Isaac, signaling 
extratropical transition could begin soon. A blend of the TAFB and 
SAB Dvorak Current Intensity estimates with objective UW-CIMSS 
estimates supports lowering the intensity to 70 kt.

As Isaac moves deeper into the mid-latitudes, it will cross even
cooler waters and encounter increasing deep-layer shear. Thus,
continued weakening is likely, and Isaac is expected to lose
tropical characteristics soon and complete extratropical transition
by Monday while becoming entangled with a nearby frontal system. The
updated NHC forecast shows a faster rate of weakening in the near
term. The wind radii of Isaac are likely to become increasingly
asymmetric as the cyclone takes on frontal characteristics.

Isaac is moving northeastward at about 13 kt. This general motion
should continue for the next couple of days while Isaac remains
embedded in deep-layer southwesterly flow. The storm is forecast to
turn more north-northeastward by midweek as an upper-level trough
digs to the west of Isaac. There is more track spread in the
guidance related to this interaction, and the extratropical portion
of the NHC track forecast was adjusted slightly to the right of the
previous prediction, following the latest multi-model consensus
trends.


FORECAST POSITIONS AND MAX WINDS

INIT  29/0300Z 42.1N  37.6W   70 KT  80 MPH
12H  29/1200Z 43.1N  36.3W   65 KT  75 MPH
24H  30/0000Z 44.2N  33.7W   55 KT  65 MPH...POST-TROPICAL
36H  30/1200Z 45.4N  30.6W   50 KT  60 MPH...POST-TROP/EXTRATROP
48H  01/0000Z 47.1N  28.3W   45 KT  50 MPH...POST-TROP/EXTRATROP
60H  01/1200Z 49.2N  27.1W   40 KT  45 MPH...POST-TROP/EXTRATROP
72H  02/0000Z 51.1N  26.3W   40 KT  45 MPH...POST-TROP/EXTRATROP
96H  03/0000Z 55.0N  24.4W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  04/0000Z 58.0N  20.0W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Reinhart