[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 211438
TCDAT4

HURRICANE DANNY DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042015
1100 AM AST FRI AUG 21 2015

Danny has continued to strengthen during the past several hours.
The small eye has become better defined, and it is now embedded in
a circular central dense overcast.  In addition, the ragged outer
banding has increased in coverage and now surrounds the central
convection.  The initial intensity is increased to 90 kt in
agreement with satellite intensity estimates from TAFB and SAB.  It
is notable that experimental multispectral METEOSAT imagery suggests
that low-level moisture has wrapped around the cyclone and pushed
the drier air farther away.  This could be helping both the
intensification and the increase in outer banding.

The initial motion is 290/9.  The subtropical ridge north of Danny
remains weaker than normal due to a deep-layer trough over the
western Atlantic.  This trough is expected to lift northward in a
couple of days, allowing the ridge to build westward and
strengthen.  This evolution should cause Danny to turn more
westward with some increase in forward speed.  The track guidance
is in good agreement with this scenario and forecasts Danny to be
near the Leeward Islands in about 72 hours, near Puerto Rico in
about 96 hours, and near Hispaniola in about 120 hours.  The new
forecast track, which is in best agreement with the GFS and ECMWF
models, lies close to the previous forecast through 96 hours and a
little to the north of the previous forecast at 120 hours.

Danny is currently in an environment of light vertical wind shear.
However, it is about to encounter increasing upper-level
southwesterly flow associated with a trough over the northeastern
Caribbean, with the shear forecast to increase to over 20 kt by 96
hours.  This, combined with the abundant dry air remaining along the
forecast track, should cause Danny to weaken below hurricane
strength as it approaches the Caribbean islands.  The new intensity
forecast is a little stronger than the intensity consensus through
96 hours.  After that, it is weaker than most of the guidance due
to the expected interaction with land.

A NOAA aircraft will be conducting a research mission in and around
Danny this afternoon, and an Air Force Reserve Unit reconnaissance
aircraft will investigate Danny Saturday afternoon.  These data
will provide a better assessment of the intensity and structure of
the hurricane.


FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 14.0N  48.2W   90 KT 105 MPH
 12H  22/0000Z 14.5N  49.6W   90 KT 105 MPH
 24H  22/1200Z 15.1N  51.7W   85 KT 100 MPH
 36H  23/0000Z 15.5N  54.0W   75 KT  85 MPH
 48H  23/1200Z 16.0N  56.4W   65 KT  75 MPH
 72H  24/1200Z 17.0N  61.5W   55 KT  65 MPH
 96H  25/1200Z 18.0N  66.0W   50 KT  60 MPH
120H  26/1200Z 19.5N  71.0W   40 KT  45 MPH...INLAND

$$
Forecaster Beven
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