Tropical Depression Guillermo Discussion Number 12
NWS National Hurricane Center Miami FL EP072021
200 AM PDT Tue Jul 20 2021
Aside from an isolated shower or two, the cyclone has been
essentially devoid of deep convection for the past 12-15 hours. A
recent scatterometer overpass measured winds of 27 kt over the
northern portion of the circulation, and assuming some undersampling
by that instrument the advisory intensity remains 30 kt.
Guillermo has been moving just slightly south of due west or around
260/15 kt. A mid-level ridge to the north and northwest of the
system should result in a westward to west-southwestward track
during the next couple of days. The official forecast is just a bit
south of the previous track and follows the latest multi-model
consensus, TVCE, solution.
The cyclone is expected to traverse SSTs of 24-25 deg C during the
next couple of days, and continue to ingest relatively dry and
stable air as evidenced by the dense stratocumulus field ahead of
the system. These conditions should make it unlikely for Guillermo
to regenerate. Unless there is a significant redevelopment of deep
convection near the center soon, Guillermo will be declared a
remnant low pressure system later today.
Post-Tropical Cyclone Guillermo Discussion Number 14
NWS National Hurricane Center Miami FL EP072021
200 PM PDT Tue Jul 20 2021
Guillermo's circulation consists of a tight swirl of low-level
clouds, and the earlier brief convective flare up dissipated
shortly after the release of the previous advisory. Given that
the system has been devoid of organized deep convection for most of
the last 18 hours, the system is now considered a remnant low and
this will be the last NHC advisory. The initial intensity remains
30 kt based on a recent ASCAT pass that showed an area of 25-30 kt
winds north of the center.
The post-tropical cyclone will remain in an dry, stable airmass
while moving over SSTs of 24-25C, which should result in a gradual
spin down of the circulation. Global model fields indicate that the
low will open up into a trough within 48-60 hours, and that is
indicated in the official forecast.
The remnant low is now moving a little south of due west, with an
initial motion estimate of 265/15. The system is expected to move
west-southwestward until dissipation under the influence of the
expansive low-level ridge centered over the north-central Pacific.
The new NHC track forecast is a little south of and faster than the
previous one, trending toward the latest consensus aids.
