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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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