[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 212043
TCDAT4

HURRICANE DANNY DISCUSSION NUMBER  14
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042015
500 PM AST FRI AUG 21 2015

A NOAA Hurricane Hunter aircraft investigated Danny around
1600-1730 UTC.  It found winds as high as 111 kt at the 12,000 ft
flight level and surface wind estimates from the Stepped Frequency
Microwave Radiometer as high as 104 kt.  It also reported a
dropsonde central pressure of 974 mb.  Based on these data, Danny
reached a 100-kt intensity at that time.  Since then, the eye has
disappeared in satellite imagery, and the cyclone is showing signs
of being affected by southwesterly vertical wind shear.  The
initial intensity is 100 kt for this advisory based on an expected
lag between the decay of the cloud pattern and the cyclone's
weakening.  That being said, this intensity could be generous.

The initial motion is now 295/9.  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 during
the next 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 and
the Virgin Islands in about 84-96 hours, and in the vicinity of
Hispaniola by day 5.  The new forecast track has a noise-level nudge
to the north of the previous forecast and is in best agreement with
the GFS and ECMWF models.  It lies just south of the center of the
guidance envelope.

Danny has likely peaked in intensity based on the signs of shear in
the cloud pattern, stronger upper-level winds present west of the
cyclone, and abundant nearby dry air.  Although it starts from a
higher initial intensity than the previous forecast, the new
intensity forecast still calls for Danny to weaken below hurricane
strength at about 48 hours.  After that, the system should continue
to weaken as it moves near or over the Greater Antilles in close
proximity to an upper-level trough.  The GFS/ECWMF/UKMET models
all forecast Danny to degenerate to a tropical wave by 120 hours, so
the new intensity forecast compromises between this extreme and the
SHIPS/LGEM models, which forecast a stronger cyclone at that time.

NOAA and Air Force Reserve Unit reconnaissance aircraft will
investigate Danny again Saturday afternoon.  These data will provide
a better assessment of the intensity and structure of the hurricane.


FORECAST POSITIONS AND MAX WINDS

INIT  21/2100Z 14.5N  49.1W  100 KT 115 MPH
 12H  22/0600Z 15.0N  50.5W   95 KT 110 MPH
 24H  22/1800Z 15.5N  52.7W   85 KT 100 MPH
 36H  23/0600Z 15.9N  55.2W   70 KT  80 MPH
 48H  23/1800Z 16.3N  57.8W   60 KT  70 MPH
 72H  24/1800Z 17.5N  62.5W   55 KT  65 MPH
 96H  25/1800Z 18.5N  67.0W   50 KT  60 MPH
120H  26/1800Z 19.5N  71.5W   35 KT  40 MPH...INLAND

$$
Forecaster Beven
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