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Tropical Depression Gilma Discussion Number   9
NWS National Hurricane Center Miami FL       EP082018
200 PM PDT Sat Jul 28 2018

Increasing westerly shear is taking its toll on Gilma.  Deep
convection that has been persisting on the eastern side of the
system has become farther separated from the center, with an exposed
low-level swirl centered more than 75 n mi from the edge of
the convection.  Although the system appears to be a little weaker
than earlier today, there is no scatterometer data to confirm that.
Therefore, the initial wind speed has been held at 30 kt, in
agreement with the Dvorak classifications of 2.0/30 kt from both
TAFB and SAB.

Westerly shear of about 30 to 35 kt is expected to continue during
the next few days, and the global models indicate that the
upper-level flow should become less diffluent as Gilma passes west
of the axis of an upper-level trough tonight.  The combination of
these hostile winds aloft, cooler SSTs, and a more stable air mass
should cause Gilma to gradually weaken, and the NHC forecast
now shows Gilma becoming a remnant low in about 24 hours and
degenerating into a trough by day 4.  Gilma could become a remnant
low even sooner than currently forecast, as the unfavorable
upper-level flow to the west of the upper trough axis could
completely shear off the deep convection from the center.

The depression made a jog to the northwest during the day today,
but it is expected to resume a west to west-northwestward motion
at around 10 kt through tonight, steered by mid-level ridging
to the north.  Thereafter, as the system becomes increasingly
shallow, it should turn to the west, steered by low-level ridging to
its northwest. The NHC forecast track is very close to the previous
forecast, and it is close to the clustering of the consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  28/2100Z 15.8N 134.3W   30 KT  35 MPH
 12H  29/0600Z 16.0N 135.6W   30 KT  35 MPH
 24H  29/1800Z 16.3N 137.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  30/0600Z 16.3N 139.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  30/1800Z 16.1N 141.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  31/1800Z 15.7N 145.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  01/1800Z...DISSIPATED

$$
Forecaster Cangialosi/Latto

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