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Tropical Storm Bud Discussion Number  20
NWS National Hurricane Center Miami FL       EP032018
900 AM MDT Thu Jun 14 2018

Bud's overall structure and convective pattern have changed little
since the previous advisory, with the tropical storm consisting of
mainly a large swirl of low clouds and fragmented cyclonically
curved bands of moderate convection. Despite this unimpressive
satellite appearance, Bud is still producing tropical-storm-force
winds in the the convective band in the northern semicircle. A
Mexican Navy automated weather station in the port of Cabo San Lucas
recently reported a 2-minute average wind of 39 kt and a gust to 53
kt, and also reported 36-kt winds for a 5-minute period shortly
after 1200 UTC. The observing site has also recorded a pressure of
1004.5 mb thus far. Based on these wind data, the initial intensity
is being maintained at 40 kt for this advisory, and the central
pressure is estimated to be 1000 mb.

Bud has a broad inner-core wind field and a small-scale vortex has
been rotating counter-clockwise within the larger cyclonic gyre.
After smoothing through all the wobbles of the center, a motion
of 345/06 kt is computed over the past 18 hours. No significant
changes were made to the previous track forecast. The model guidance
is tightly packed around the previous advisory track and remains in
excellent agreement that Bud will gradually turn northward during
the next 36 hours around the western periphery of a deep-layer ridge
located across north-central Mexico. A turn toward the
north-northeast is expected by 48 hours as the steering flow becomes
more southwesterly ahead of an approaching mid-level trough, which
will also act to accelerate Bud. The new NHC forecast track is just
a tad to the west of the previous track through 24 hours, and lies
along the eastern edge of the guidance envelope.

During the next 24 hours, Bud will be moving over cool waters and
interacting with the mountainous terrain of southern Baja
California, which should result in a gradual erosion of the deep
convection and spin down of the circulation. Some enhanced wind flow
in the northeastern quadrant due to funneling between Bud's center
and the higher terrain of mainland Mexico is possible once Bud's
center emerges over the Gulf of California in 24 hours. For that
reason, Bud is being maintained as a tropical depression until the
second landfall occurs in about 36 hours. After landfall, rapid
weakening and dissipation by 48 hours is expected over the high
terrain of mainland Mexico.

Despite weakening or dissipation, Bud's remnant moisture plume is
expected to spread northward and northeastward into northwestern
Mexico and the U.S. Desert Southwest on Friday and Saturday,
resulting in significant rainfall and possible flash flooding across
those areas.  For further information on the heavy rainfall threat,
please see products issued by your local weather service office.

FORECAST POSITIONS AND MAX WINDS

INIT  14/1500Z 21.7N 109.6W   40 KT  45 MPH
 12H  15/0000Z 22.8N 109.9W   35 KT  40 MPH
 24H  15/1200Z 24.6N 110.3W   30 KT  35 MPH
 36H  16/0000Z 27.0N 110.3W   25 KT  30 MPH
 48H  16/1200Z 29.4N 110.1W   20 KT  25 MPH...POST-TROP/INLAND
 72H  17/1200Z...DISSIPATED

$$
Forecaster Stewart

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