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Tropical Storm Iselle Discussion Number  11
NWS National Hurricane Center Miami FL       EP142020
800 PM PDT Fri Aug 28 2020
 
Persistent bursts of deep convection continue to develop just to 
the west of Iselle's center, which occasionally becomes hidden 
beneath the cirrus outflow (as it is now).  Dvorak final-T numbers 
from TAFB and SAB are 3.0/45 kt based on a shear pattern, and along 
with what was shown by an afternoon ASCAT pass, Iselle's intensity 
remains 45 kt.  Strong shear from the east-northeast is forecast to 
continue for the next 24 hours or so.  After that time, the shear 
should relax, but then the thermodynamic environment becomes more 
limiting with Iselle moving over sub-26C waters and into a much more 
stable environment.  All told, Iselle is expected to steadily weaken 
during the next several days, and it is likely to degenerate into a 
remnant low on Sunday.  The NHC forecast is very similar to the 
previous prediction and is close to HCCA and the IVCN intensity 
consensus aid.  The remnant low is expected to dissipate in about 4 
days.

Iselle is moving slowly north-northeastward (015/5 kt) on the 
western periphery of a low- to mid-level area of high pressure 
centered over Mexico.  This high, along with a trough extending off 
the coast of California, should cause Iselle to gradually turn 
toward the north and then north-northwest with some increase in 
forward speed during the next couple of days.  There is a typical 
amount of spread among the track models, and they generally agree 
on this northward motion with a slight bend to the left through the 
forecast period.  The regional hurricane models appear almost in a 
cluster all to themselves on the eastern side of the guidance 
envelope, and the NHC forecast therefore closely follows the TVDG 
model consensus aid, which gives double weight to the global models.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/0300Z 19.3N 115.2W   45 KT  50 MPH
 12H  29/1200Z 20.2N 115.0W   40 KT  45 MPH
 24H  30/0000Z 21.7N 115.0W   35 KT  40 MPH
 36H  30/1200Z 23.1N 115.4W   30 KT  35 MPH
 48H  31/0000Z 24.2N 115.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  31/1200Z 24.9N 116.4W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  01/0000Z 25.6N 116.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  02/0000Z...DISSIPATED
 
$$
Forecaster Berg
 
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