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Tropical Storm Isaac Discussion Number  16
NWS National Hurricane Center Miami FL       AL102024
900 PM GMT Sun Sep 29 2024
 
The increasingly hostile sea surface temperatures, strong vertical
wind shear, and dry air wrapping around the southern half of Isaac
has weakened the cyclone. The last few visible stallite images
before sundown suggest that the vortex could be tilted, with the
low-level center displaced southwest of the upper-level vortex.
Additionally, deep convection has become less symmetric since the
last advisory, with convection in the southern semicircle likely
being cut off by the aformentioned dry air. This structure is
indicative of a progressing extratropical transition, as Isaac
continues to interact with a baroclinic frontal zone to its
northeast. The initial intensity is set to 60 kt for this advisory,
which is a blend of the subjective and objective satellite
classifications.
 
Tropical Storm Isaac is forecast to continue its extratropical
transition and become a fully extratropical cyclone on Monday. This
is in agreement with model-diagnosed thermodynamics that maintain a
warm core until this time, in addition to simulated IR satellite
data from the GFS and ECMWF models. The intensity forecast is
similar to the previous forecast and shows a steady decrease in
maximum sustained winds through the forecast period.
 
The forward motion of the cyclone continues to be northeastward
(050/10 kt). This general motion is forecast to continue for the
next day or so as Isaac continues to be steered by a mid-level
trough to its west. This mid-level trough will steer Isaac towards
the north-northeast beyond 36 hr. Beyond 96 hr, global model data
indicates Isaac will be absorbed by a more potent extratropical
cyclone just southeast of Iceland. The track forecast is again
adjusted eastward from the previous advisory.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/2100Z 43.8N  34.7W   60 KT  70 MPH
 12H  30/0600Z 44.6N  32.4W   55 KT  65 MPH
 24H  30/1800Z 45.8N  28.6W   50 KT  60 MPH...POST-TROP/EXTRATROP
 36H  01/0600Z 47.4N  25.8W   45 KT  50 MPH...POST-TROP/EXTRATROP
 48H  01/1800Z 49.3N  24.2W   40 KT  45 MPH...POST-TROP/EXTRATROP
 60H  02/0600Z 51.4N  23.2W   35 KT  40 MPH...POST-TROP/EXTRATROP
 72H  02/1800Z 53.1N  22.3W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  03/1800Z 57.9N  17.9W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  04/1800Z...DISSIPATED
 
$$
Forecaster Mahoney/Blake
 
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