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Tropical Storm Guillermo Discussion Number   5
NWS National Hurricane Center Miami FL       EP072021
900 AM MDT Sun Jul 18 2021
 
Guillermo's structure has changed little this morning.  Very cold 
overshooting cloud tops associated with deep convection have been 
observed near the center of the tropical storm during the past 
couple of hours, however most of the convective activity is still 
limited to bands extending to the east and south of the tropical 
cyclone. Dvorak intensity estimates from TAFB and SAB continue to 
support an intensity estimate of 45 kt. Slight strengthening is 
anticipated over the next 24 to 36 hours while Guillermo moves over 
fairly warm waters. The rate of strengthening will likely be limited 
by moderate northwesterly shear (10-20 kt based on SHIPS 
diagnostics) and the relatively large size of the system.  After 
that, Guillermo will move over progressively cooler waters and into 
a drier more stable environment which should cause it to slowly 
weaken through the middle of the week. The GFS and HWRF forecast 
that Guillermo will maintain tropical characteristics through the 
end of the week, and this is reflected in the NHC forecast. 
However, it is also possible it will become a remnant low by the 
end of the forecast period.
 
The low-level center of Guillermo is obscured by nearby convection, 
but it appears that the tropical storm is still moving 
west-northwestward, more or less right on the previous forecast 
track. Consequently no changes of note were made to the official 
track forecast.  A mid-level ridge to the north of Guillermo will 
steer the cyclone westward for the next several days, likely with a 
slight increase in its forward speed. Around day 4 or 5, Guillermo 
is expected to weaken sufficiently so that it will become steered 
primarily by low-level flow, and a slight bend toward the 
west-southwest is anticipated. Like the previous advisory, the NHC 
forecast is very near but just barely slower than the latest 
multi-model consensus.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/1500Z 17.9N 112.5W   45 KT  50 MPH
 12H  19/0000Z 18.3N 114.2W   50 KT  60 MPH
 24H  19/1200Z 18.6N 116.8W   55 KT  65 MPH
 36H  20/0000Z 18.7N 119.6W   55 KT  65 MPH
 48H  20/1200Z 18.7N 122.5W   50 KT  60 MPH
 60H  21/0000Z 18.6N 125.5W   40 KT  45 MPH
 72H  21/1200Z 18.4N 128.4W   35 KT  40 MPH
 96H  22/1200Z 17.9N 133.4W   30 KT  35 MPH
120H  23/1200Z 17.5N 138.5W   30 KT  35 MPH
 
$$
Forecaster Zelinsky
 
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