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TROPICAL STORM POLO DISCUSSION NUMBER  16
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172014
800 PM PDT FRI SEP 19 2014

An SSM/I pass around 2200 UTC and late-day visible imagery indicated
that the center of Polo was exposed on the northeastern edge of the
deep convection. The cloud pattern has deteriorated quite a bit
during the past few hours, with little structure seen in the warming
cloud tops as they are pushed south and west of the center by about
30 kt of easterly shear. The initial intensity has been lowered to
50 kt based on a blend of the latest Dvorak Final-T and CI numbers
from TAFB and SAB. Steady weakening is forecast as the shear is
expected to continue and the cyclone will be moving into a drier
environment over gradually cooler SSTs during the next few days.
Polo should become a remnant low in about 3 days west of the Baja
California peninsula. The NHC intensity forecast has been adjusted
downward from the previous one and is close to the latest IVCN
consensus.

The initial motion is a somewhat uncertain 305/07 given the erratic
movement of the center in the last 12 to 18 hours. Polo should
gradually turn west-northwestward in the next 24 hours as a mid-
level ridge builds north of the tropical cyclone. Late in the
period, much of the guidance shows the shallow remnant low turning
south-southwestward as a low-level ridge to the west becomes the
dominant steering mechanism. The new NHC forecast has been adjusted
a little to the right in the first 48 hours given the center
position and motion, and lies a little north of a blend of the GFS
and ECMWF models. Late in the period, the NHC forecast has been
adjusted toward the south, but not as far south as the GFS and ECMWF
tracks.

Even with the slight northward shift in the track, tropical storm
force winds are likely to remain south of the Baja California
peninsula since Polo is now forecast to weaken a little faster.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 20.1N 108.2W   50 KT  60 MPH
 12H  20/1200Z 20.7N 109.1W   45 KT  50 MPH
 24H  21/0000Z 21.3N 110.4W   40 KT  45 MPH
 36H  21/1200Z 21.9N 111.7W   35 KT  40 MPH
 48H  22/0000Z 22.3N 112.9W   30 KT  35 MPH
 72H  23/0000Z 22.4N 114.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  24/0000Z 22.0N 115.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  25/0000Z 21.0N 116.0W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brennan

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