[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 142040
TCDAT2

TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
500 PM AST WED SEP 14 2016

The depression has not become better organized since the last
advisory, with the most concentrated convection now in a cluster
just west of the estimated center position.  The initial intensity
remains 30 kt in best agreement with a satellite intensity estimate
from SAB.

The initial motion is a somewhat uncertain 295/13 kt.  A low- to
mid-level ridge should steer the system west-northwestward and then
westward during the forecast period, with some decrease in forward
speed after 36-48 hours as the ridge weakens slightly.  The new
forecast track is similar to, but a little north of, the previous
track based on a slight northward shift in the track guidance.

Some strengthening is expected during the next 12 hours or so. After
that, the cyclone will encounter strong westerly vertical wind shear
caused by a developing upper-level trough near and north of the
cyclone.  This, combined with passage over sea-surface temperatures
of about 26C-27C, should lead to weakening, and the intensity
forecast shows the system weakening back to a depression by 36
hours.  Near the end of the forecast period, the dynamical models
continue to diverge on the evolution of the upper-level winds, with
the ECMWF and UKMET forecasting a more favorable ridge pattern near
the cyclone, whereas the GFS has an upper-level trough close by.
Based on these conflicting models, the forecast leans toward the
ECMWF/UKMET scenario and shows some re-intensification by 120 hours.
An alternative scenario is that the cyclone degenerates into a broad
low pressure area or tropical wave as forecast by the GFS.  Overall,
the intensity forecast remains on the low side of the guidance in
best agreement with the LGEM.

Gusty winds remain possible over the Cabo Verde Islands tonight,
whereas locally heavy rains will remain possible through Thursday.

FORECAST POSITIONS AND MAX WINDS

INIT  14/2100Z 17.4N  26.5W   30 KT  35 MPH
 12H  15/0600Z 17.9N  28.4W   35 KT  40 MPH
 24H  15/1800Z 18.0N  30.8W   35 KT  40 MPH
 36H  16/0600Z 18.1N  33.2W   30 KT  35 MPH
 48H  16/1800Z 18.1N  35.6W   30 KT  35 MPH
 72H  17/1800Z 18.0N  39.5W   30 KT  35 MPH
 96H  18/1800Z 17.5N  43.5W   35 KT  40 MPH
120H  19/1800Z 18.0N  47.5W   40 KT  45 MPH

$$
Forecaster Beven
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