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Tropical Depression SIX


Tropical Depression Six Discussion Number   6
NWS National Hurricane Center Miami FL       AL062018
500 PM AST Fri Aug 31 2018

High resolution satellite images reveal that the disturbance has
developed a well-defined circulation with a cyclonically curved
convective band near the center, and plenty of showers in the
southern semicircle. The surface pressure in the Cabo Verde Island
of Santiago dropped to 1005 mb at 1800 UTC as the cyclone passed to
its south. In addition, Dvorak numbers are gradually increasing, and
now support classifying the system as a tropical depression.

The depression is becoming better organized, and it will most likely
reach tropical storm status in the next several hours.  The
environmental conditions are favorable for some strengthening during
the next 2 to 3 days while the shear is low.  Later in the forecast
period, the shear is expected to increase, and the SSTs will become
marginal halting the strengthing process. The models, primarily the
HWRF, are a little less aggressive with the intensity, so the NHC
forecast is adjusted slightly downward.

Now that the center has formed, we have a better estimate of the
initial motion, which is toward the west or 270 degrees at 13 kt.
The depression is gradually becoming steered by the flow around the
subtropical ridge, and consequently it has increased its forward
speed. This prevailing flow pattern should keep the cyclone on a
general west to west-northwest track for the next 2 to 3 days. After
that time, a weakness in the ridge will induce a more northwestward
to north-northwestward track over the open Atlantic Ocean.  The
track guidance is very consistent with this solution mainly for the
next 3 days.  Thereafter, the confidence in the track forecast
decreases as the guidance envelope widens and becomes bounded by the
westernmost ECMWF and the easternmost HWFI.  The NHC forecast
continues to be in the middle of the envelope and is very close
to the corrected consensus HCCA, which has had great skill so far
this year.


INIT  31/2100Z 13.8N  24.7W   30 KT  35 MPH
 12H  01/0600Z 14.3N  26.7W   35 KT  40 MPH
 24H  01/1800Z 14.9N  29.2W   40 KT  45 MPH
 36H  02/0600Z 15.8N  31.8W   45 KT  50 MPH
 48H  02/1800Z 16.5N  34.5W   50 KT  60 MPH
 72H  03/1800Z 18.0N  39.5W   55 KT  65 MPH
 96H  04/1800Z 20.0N  44.0W   60 KT  70 MPH
120H  05/1800Z 23.0N  48.0W   55 KT  65 MPH

Forecaster Avila