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Tropical Storm Pilar Discussion Number   3
NWS National Hurricane Center Miami FL       EP182017
400 AM CDT Sun Sep 24 2017

Recent microwave imagery from an AMSU overpass indicate that the
low-level structure of Pilar is rather messy.  It is possible that
the low-level center may be reforming under the convection to the
west, but there have been no recent higher resolution microwave or
ASCAT overpasses to confirm this.  Despite this, a blend of Dvorak
estimates from TAFB and SAB now supports an initial intensity of 40
kt.  Given a lack of any other data to go off of, that has been used
as the basis for the initial intensity.

The initial motion estimate is a highly uncertain 335/4 kt, based in
part on extrapolation from the previous motion.  There is still a
high spread among the models in the first 24 h of the forecast.
Several models, including the GFS, forecast that Pilar will move
quickly inland and dissipate. A few others, like the HWRF, keep the
center of Pilar just far enough offshore to maintain a coherent
vortex for about 72 hours. Finally, the ECMWF is an outlier in
showing Pilar reforming to the west and stalling off the west coast
of Jalisco for 24 h before moving inland and dissipating.  In the
interest of continuity, the NHC forecast for this advisory does not
account for any reformation of the center, and shows Pilar moving
steadily northward to north-northwestward until dissipation, like
the HWRF. The NHC forecast is close to the multi-model consensus,
though in this case so many members quickly show dissipation, that
relatively few members are averaged together.

The intensity forecast is also complicated by land interaction. SSTs
near the southwest coast of Mexico are very warm, and the shear is
forecast to remain low for about 36 h.  The NHC intensity forecast
only shows slight intensification since significant land interaction
is still expected.  In the event that Pilar stays farther offshore,
it could become stronger than currently forecast. Regardless of how
much Pilar intensifies, a sharp increase in shear around 48 h should
quickly cause the cyclone to weaken to a remnant low and eventually
dissipate.


FORECAST POSITIONS AND MAX WINDS

INIT  24/0900Z 19.1N 105.6W   40 KT  45 MPH
 12H  24/1800Z 19.5N 105.8W   45 KT  50 MPH
 24H  25/0600Z 20.2N 105.9W   45 KT  50 MPH
 36H  25/1800Z 21.0N 105.8W   40 KT  45 MPH
 48H  26/0600Z 22.0N 106.0W   30 KT  35 MPH
 72H  27/0600Z 24.0N 107.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  28/0600Z...DISSIPATED

$$
Forecaster Zelinsky

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