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Tropical Storm Guillermo Discussion Number 8
NWS National Hurricane Center Miami FL EP072021
1100 PM HST Sun Jul 18 2021
Guillermo is not a well-organized tropical cyclone. The low-level
center is displaced about 90 n mi to the northwest of the main area
of deep convection due to northwesterly shear. Taking the mean of
Dvorak final T and current intensity numbers from TAFB and SAB
gives 40 kt, and scatterometer data from a few hours ago suggest
that this may be a generous estimate for the advisory intensity.
Using center fixes from geostationary and microwave imagery along
with the scatterometer winds gives a westward initial motion, or
about 270/13 kt. A well-defined mid-level ridge of high pressure
to the north of the cyclone should maintain a generally westward
motion throughout the forecast period. The official forecast track
is nudged slightly south of the previous one, mainly on account of
the short-term motion. This track forecast is very close to the
latest dynamical model consensus, TVCE, which is usually a very
good performer.
Assuming that some deep convection redevelops nearer to the center
over the next day or two, Guillermo may be able to maintain some of
its intensity for a while. Also, the relatively large circulation
should take some time to spin down as shown by the global models.
However, gradually cooling SSTs, dry mid-level air and continued
shear are expected to cause the cyclone to weaken to a depression in
a couple of days and to degenerate into a remnant low by the end of
the forecast period, if not sooner. The official intensity forecast
is similar to the numerical consensus, IVCN.
FORECAST POSITIONS AND MAX WINDS
INIT 19/0900Z 18.8N 116.8W 40 KT 45 MPH
12H 19/1800Z 18.9N 118.9W 40 KT 45 MPH
24H 20/0600Z 18.9N 121.7W 40 KT 45 MPH
36H 20/1800Z 18.7N 124.6W 35 KT 40 MPH
48H 21/0600Z 18.5N 127.5W 35 KT 40 MPH
60H 21/1800Z 18.3N 130.3W 30 KT 35 MPH
72H 22/0600Z 18.2N 132.8W 25 KT 30 MPH
96H 23/0600Z 18.2N 137.8W 25 KT 30 MPH
120H 24/0600Z 18.0N 144.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
$$
Forecaster Pasch
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