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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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