[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 221457
TCDAT4

HURRICANE DANNY DISCUSSION NUMBER  17
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042015
1100 AM AST SAT AUG 22 2015

Danny's cloud pattern is similar to that of six hours ago, with a
central dense overcast and some outer banding in the northeastern
semicircle.  However, the size of the overcast has diminished with
the center getting closer to the edge.  The initial intensity is
decreased to 80 kt based on decreasing satellite intensity
estimates and continuity from the previous advisory.  However, this
could be generous.  NOAA and Air Force Reserve Unit reconnaissance
aircraft are scheduled to investigate Danny this afternoon and
should provide a better estimate of its intensity.

The initial motion is now 285/10.  There is no change in the
forecast philosophy from the previous advisory, with Danny expected
to turn westward and accelerate later today as the subtropical ridge
to the north of the cyclone builds westward and strengthens.  This
general motion is expected to persist for the next several days
taking Danny across the Leeward Islands in about two days, and near
Puerto Rico and Hispaniola in 3 to 4 days.  The track model
guidance remains in good agreement with this, and the forecast
track lies near the center of the track guidance envelope.

Danny is expected to move through a dry and stable air mass and
encounter moderate to strong southwesterly vertical wind shear for
at least the next three days.  This should cause continued
weakening, and the cyclone is forecast to be a tropical storm as it
moves over or near the northeastern Caribbean Islands.  The
intensity forecast becomes lower confidence at days 4 and 5 due to
the uncertainty in how much land Danny will encounter, disagreements
between the dynamical models over the forecast shear, and continued
divergence between the models forecasting Danny to dissipate and the
models forecasting it to survive.  The latter part of the forecast
compromises between these extremes by showing a continued weakening
trend.

A tropical storm watch is being issued for portions of the Leeward
Islands at this time.  Additional watches or warning may be
necessary for this area, as well as the Virgin Islands and Puerto
Rico, later today or tonight.


FORECAST POSITIONS AND MAX WINDS

INIT  22/1500Z 15.4N  52.0W   80 KT  90 MPH
 12H  23/0000Z 15.7N  53.7W   70 KT  80 MPH
 24H  23/1200Z 16.1N  56.1W   60 KT  70 MPH
 36H  24/0000Z 16.6N  58.7W   55 KT  65 MPH
 48H  24/1200Z 17.2N  61.3W   50 KT  60 MPH
 72H  25/1200Z 18.5N  66.0W   45 KT  50 MPH
 96H  26/1200Z 20.5N  71.0W   40 KT  45 MPH
120H  27/1200Z 22.0N  75.5W   30 KT  35 MPH

$$
Forecaster Beven
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