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Tropical Depression Fifteen-E Discussion Number  10
NWS National Hurricane Center Miami FL       EP152017
800 PM PDT Wed Sep 13 2017

During the afternoon hours, the mid-level center of the depression
became completely removed from the now exposed low-level center.  A
small tight swirl embedded within a broader, elongated, low-level
circulation is still evident, but deep convection is limited to a
band displaced about 60 n mi to the west of the center.  The initial
intensity has been held at 30 kt, based on earlier ASCAT data. Given
the poor convective structure of the depression, little change in
intensity is expected for the next day or so. After that time, the
GFS and ECMWF both forecast that the upper-level wind pattern will
become more favorable for intensification.  Once that happens, most
of the intensity guidance forecasts that the cyclone will begin to
steadily strengthen, especially after about 72 h.  My forecast is a
little higher than the previous NHC forecast at 96 h and 120 h, and
is very close to IVCN.

The depression has been nearly stationary for the past 6 hours. The
initial motion estimate assumes at least some movement, and is a
rather uncertain 270/02 kt.  The global models agree that the
cyclone will remain trapped in weak steering flow throughout the
forecast period, but vary greatly on how much it will move.  A
complicating factor is that the GFS suggests that the low-level
center may reform underneath the mid-level center to the south. My
forecast assumes that the current center of circulation will
persist, but a larger change may be required if such a reformation
occurs. The new official track forecast is slower than the previous
one for the first 36 h, but is close after that, and still shows
little movement throughout the forecast period.  The track forecast
is based heavily on the ECMWF model, especially beyond day 2.

FORECAST POSITIONS AND MAX WINDS

INIT  14/0300Z 15.1N 121.3W   30 KT  35 MPH
 12H  14/1200Z 15.2N 122.1W   30 KT  35 MPH
 24H  15/0000Z 15.4N 123.1W   35 KT  40 MPH
 36H  15/1200Z 15.5N 124.0W   35 KT  40 MPH
 48H  16/0000Z 15.3N 124.8W   40 KT  45 MPH
 72H  17/0000Z 15.5N 125.5W   45 KT  50 MPH
 96H  18/0000Z 16.0N 125.5W   55 KT  65 MPH
120H  19/0000Z 16.5N 125.0W   50 KT  60 MPH

$$
Forecaster Zelinsky

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