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Tropical Storm Tara Discussion Number   9
NWS National Hurricane Center Miami FL       EP222018
1000 AM CDT Tue Oct 16 2018

A surge of moderate to strong southeasterly wind shear early this
morning decapitated Tara, with the original upper-level circulation
now displaced more than 100 nmi to the north or just east of Puerto
Vallarta. Convection waned considerably as a result of the shear and
decoupling of the low- and upper-level circulations, but
thunderstorm activity has made a little bit of comeback over the
past few hours. However, the decoupling likely resulted in
significant weakening of the tiny tropical storm, so the intensity
has been lowered to 40 kt, which is slightly higher than the 35-kt
winds noted in an earlier ScatSat scatterometer overpass.

The initial motion estimate is a highly uncertain 335/01 kt. Data
from a recent 1035Z SSMI/S overpass suggest that Tara hasn't moved
much, if at all, during the past 12 hours. The first few visible
satellite images also indicate this, and that Tara may just be a
small swirl embedded within a northwest-to-southeast elongated
trough. For now, the system is being maintained as a tiny tropical
cyclone that is expected to drift slowly northwestward along the
aforementioned surface trough axis. Almost all of the model guidance
with the exception of the HWRF and NAVGEM models dissipate the
cyclone in 24-36 hours, so the forecast track beyond 24 hours leans
heavily on continuity with the previous advisory track, along with
some input from the HWRF model. However, it is quite possible that
Tara could dissipate sooner than indicated.

The vertical shear is forecast to weaken to less than 10 kt in 12-18
hours, but there may not be enough of a circulation remaining at
that time to take advantage of the improving environment. Intrusions
of dry mid-level air along with some interaction with the
mountainous terrain of southwestern Mexico are expected to override
the favorable wind shear environment, causing Tara to weaken to a
depression within 24 hours, and degenerate into a remnant low
pressure system by 36 hours. However, weakening could occur more
rapidly than forecast due to the recent loss of vertically
structure.

Regardless of the exact track or intensity of Tara or its remnants,
heavy rainfall will continue to be a threat along the immediate
coast of southwestern Mexico due to the system's slow motion, and
life-threatening flash flooding will be possible in mountainous
areas.

FORECAST POSITIONS AND MAX WINDS

INIT  16/1500Z 18.6N 104.5W   40 KT  45 MPH
 12H  17/0000Z 18.9N 104.9W   35 KT  40 MPH
 24H  17/1200Z 19.2N 105.3W   30 KT  35 MPH
 36H  18/0000Z 19.5N 105.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  18/1200Z 19.7N 106.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  19/1200Z...DISSIPATED

$$
Forecaster Stewart

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