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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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