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Tropical Storm Guillermo Discussion Number 4
NWS National Hurricane Center Miami FL EP072021
300 AM MDT Sun Jul 18 2021
Guillermo has become a little better organized, with more deep
convection concentrated near the estimated center, and some banding
features trying to develop over the southern part of the
circulation. Upper-level outflow is fairly well-defined over the
southern semicircle as well. The latest Dvorak intensity estimates
from both TAFB and SAB are 45 kt, and this is used for the advisory
intensity. Scatterometer data from ASCAT-A suggest that this may be
a somewhat generous intensity estimate, but the ASCAT-B and ASCAT-C
sensors did not sample the strongest part of the circulation.
There is still considerable scatter in the center fixes from
geostationary imagery. Blending these fixes with additional center
positions from microwave imagery yields a slightly slower forward
motion of about 285/10 kt. A mid-level ridge should be established
to the north of Guillermo for the next several days. This is
likely to result in a generally westward track at a faster forward
speed through most of the forecast period. Late in the period, a
slight bend toward the west-southwest is expected as the weakening
cyclone is influenced more by the low-level flow. The official
track forecast is quite close to the previous one and is near, or a
little slower than, the latest multi-model consensus.
Some additional strengthening is anticipated while the system is in
a relatively low shear environment during the next day or so.
However, the SHIPS model indicates some increase in northwesterly
shear in 1-2 days. Thereafter, SSTs beneath Guillermo should
decrease. These changes should lead to a leveling off of the
intensity, followed by gradual weakening. The NHC intensity forecast
is near or above the model consensus, IVCN, and is also very similar
to the latest HWRF model prediction.
FORECAST POSITIONS AND MAX WINDS
INIT 18/0900Z 17.6N 111.6W 45 KT 50 MPH
12H 18/1800Z 18.0N 113.1W 50 KT 60 MPH
24H 19/0600Z 18.4N 115.5W 55 KT 65 MPH
36H 19/1800Z 18.7N 118.2W 55 KT 65 MPH
48H 20/0600Z 18.7N 120.9W 50 KT 60 MPH
60H 20/1800Z 18.7N 123.8W 40 KT 45 MPH
72H 21/0600Z 18.5N 126.8W 35 KT 40 MPH
96H 22/0600Z 18.0N 132.0W 30 KT 35 MPH
120H 23/0600Z 17.5N 137.0W 30 KT 35 MPH
$$
Forecaster Pasch
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