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Tropical Depression THIRTEEN-E


Tropical Depression Thirteen-E Discussion Number   2
NWS National Hurricane Center Miami FL       EP132017
200 PM PDT Fri Aug 18 2017

The tropical depression is slowly becoming more organized.  Moderate
upper-level northeasterly winds are inhibiting outflow in the
northeast quadrant of the cyclone, but banding convection is present
in all quadrants.  A pair of ASCAT passes around 1700 and 1800 UTC
confirmed that the depression has a well-defined center and showed
maximum winds of just below 30 kt.  The initial intensity
is therefore held at 30 kt.  The ASCAT data also indicated
that the center of circulation is a little to the south of the
previous estimated position, perhaps in part due to a reorganization
of the center closer to the main mass of convection.

Due to the relocation of the estimated center to the south, the
official forecast has been shifted to the south and west throughout
the forecast period.  Otherwise, the reasoning behind the forecast
has not changed, and the depression should continue to be steered
generally westward to west-northwestward for the next 3 days by a
mid-level ridge.  A weakness in the ridge is forecast to develop
around day 4 that should cause the cyclone to turn toward the
northwest and slow down.  The only change in the track guidance
is a slight increase in forward speed through 36 h, and confidence
is fairly high in the track forecast due to a tight clustering of
the global models.

No change has been made to the intensity forecast, which remains
very close to the multi-model consensus.  The light northeasterly
shear currently affecting the cyclone is forecast to decrease over
the next 12 to 24 h.  Once that happens, the cyclone will be
embedded within an environment consisting of low shear, warm SSTs,
and sufficient moisture to support strengthening. After about 72 h,
cooler waters and a more stable environment should cause steady
weakening.  By day 5, SSTs are expected to be be below 24 C, and the
cyclone will likely be close to becoming a remnant low.


INIT  18/2100Z 14.8N 117.9W   30 KT  35 MPH
 12H  19/0600Z 15.1N 119.9W   35 KT  40 MPH
 24H  19/1800Z 15.6N 122.7W   45 KT  50 MPH
 36H  20/0600Z 16.4N 125.5W   55 KT  65 MPH
 48H  20/1800Z 17.2N 128.0W   65 KT  75 MPH
 72H  21/1800Z 18.9N 131.6W   75 KT  85 MPH
 96H  22/1800Z 21.0N 133.3W   65 KT  75 MPH
120H  23/1800Z 23.9N 133.9W   45 KT  50 MPH

Forecaster Zelinsky