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Tropical Depression EIGHTEEN-E Forecast Discussion

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WTPZ43 KNHC 260243

800 PM PDT SUN SEP 25 2016

The cloud pattern of the depression has not changed much during the
last several hours.  The center of the system is partially exposed
on the west side of a convective band.  Satellite images also show
a pronounced dry slot to the west and northwest of the center.  The
Dvorak classifications remain T2.5/35 kt from TAFB and T1.5/25 kt
from SAB, and based on these estimates, the initial wind speed is
held at 30 kt.

Some slight strengthening is possible overnight or on Monday while
the system remains over warm water and in an environment of light to
moderate shear.  After that time, the environment should become less
conducive with southwesterly shear increasing to more than 20 kt in
about 24 hours, which will likely end the opportunity for
strengthening.  The system is forecast to cross the 26-deg-C
isotherm in 36 to 48 hours, and as a result, it should become a
remnant low by day 3.  The global models show the remnant low
dissipating by the end of the forecast period, and that is reflected
in the official forecast.  The new intensity forecast is a little
lower than the previous one and is in good agreement with the latest
intensity model consensus.

The center of the depression has wobbled a bit to the west of the
previous track, and the current motion estimate is 345/6 kt. A large
cut-off mid- to upper-level low over northwestern Mexico is expected
to drift southwestward during the next day or two.  This should
cause the system to turn north-northeastward to northeastward on
Monday, and continue in that general direction through mid-week.
Once the system becomes a shallow remnant low, a turn to the
west-northwest is predicted, following the low-level trade wind
flow.  The NHC track forecast is not too different from the previous
one, and is in best agreement with the GFS ensemble mean and a
consensus of the GFS and ECMWF models.


INIT  26/0300Z 16.7N 120.1W   30 KT  35 MPH
 12H  26/1200Z 17.2N 119.8W   35 KT  40 MPH
 24H  27/0000Z 17.8N 119.4W   35 KT  40 MPH
 36H  27/1200Z 18.7N 118.7W   35 KT  40 MPH
 48H  28/0000Z 19.9N 118.0W   30 KT  35 MPH
 72H  29/0000Z 22.6N 117.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  30/0000Z 24.6N 119.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  01/0000Z...DISSIPATED

Forecaster Cangialosi