Issued at 500 AM HST Mon Jul 19 2021

WTPZ42 KNHC 191437

Tropical Storm Guillermo Discussion Number 9
NWS National Hurricane Center Miami FL EP072021
500 AM HST Mon Jul 19 2021

Guillermo's satellite presentation has continued to deteriorate
over the past several hours, although a new, small deep convective
burst has developed just to the southeast of the circulation
center. An earlier AMSR2 microwave overpass revealed a rather
elongated (west to east) and ill-defined circulation with
fragmented bands in the southeast quadrant. The initial intensity
is lowered to 35 kt and is based on a blend of the TAFB and SAB
Dvorak satellite intensity estimates.

Guillermo is moving over cooler (about 25C) water and into a
progressively more stable and drier surrounding environment.
The statistical-dynamical SHIPS models (GFS/ECMWF) indicate that
moderate west-northwesterly shear should also contribute to the
cyclone's degeneration to a remnant low on Wednesday night. The
intensity forecast now shows Guillermo becoming a remnant low
sooner than the previous advisory and conforms with a consensus of
the large-scale models and the SHIPS forecasts.

The initial motion is estimated to be westward, or 275/13 kt. A
subtropical ridge anchored to the north of the cyclone should
influence a generally westward motion through dissipation at day 5.
A few of the global models are now showing the lower levels
of the ridge building some to the east-northeast of the Hawaiian
Islands which could induce a west-southwestward motion, or slightly
left of due west, around mid-period. The NHC forecast is once
again adjusted a bit to the left of the previous one and is based on
the various consensus aids.


INIT 19/1500Z 19.1N 117.8W 35 KT 40 MPH
12H 20/0000Z 19.0N 119.9W 35 KT 40 MPH
24H 20/1200Z 18.9N 123.0W 30 KT 35 MPH
36H 21/0000Z 18.6N 126.1W 30 KT 35 MPH
48H 21/1200Z 18.3N 128.9W 30 KT 35 MPH
60H 22/0000Z 18.1N 131.4W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 22/1200Z 17.9N 134.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 23/1200Z 17.9N 139.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 24/1200Z 17.9N 145.6W 25 KT 30 MPH...POST-TROP/REMNT LOW

Forecaster Roberts

Source: Tropical Storm Guillermo Forecast Discussion Number 9