[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 231436
TCDAT4

TROPICAL STORM DANNY DISCUSSION NUMBER  21
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042015
1100 AM AST SUN AUG 23 2015

Danny appears to be maintaining its intensity for now.  The
low-level center is estimated to be near the southwestern edge of
the main mass of deep convection, and considerable lightning
activity has recently been occurring near the center.  The current
intensity estimate is held at 45 kt in agreement with the latest
Dvorak estimates and earlier Hurricane Hunter aircraft data.  The
center of the storm should pass very near, or over, the French data
buoy 41300 shortly, and this should provide additional information
about the intensity.  Southwesterly vertical shear of nearly 20 kt
along with dry mid-level air should continue to affect Danny over
the next couple of days.  Both the GFS and ECMWF global models
continue to depict the system opening up into a wave within 48
hours.  Given these unfavorable signs, the official forecast shows
weakening as in the previous advisories.  However, because of the
uncertainties in tropical cyclone intensity prediction, it is
prudent to issue a tropical storm watch for Puerto Rico and the
U.S. Virgin Islands at this time.

Danny continues westward, or 275/13 kt.  A westward to west-
northwestward track is expected over the next few days as the
cyclone moves on the southern side of a low- to mid-level ridge.
The track model guidance has shifted a little south on this cycle,
and so has the official forecast.  This is close to the latest
dynamical model consensus.  If Danny weakens faster than expected,
it could move even farther south of this track.

The system could bring much-needed rainfall to Puerto Rico over the
next few days.

FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z 15.8N  57.3W   45 KT  50 MPH
 12H  24/0000Z 16.0N  59.3W   40 KT  45 MPH
 24H  24/1200Z 16.5N  61.9W   35 KT  40 MPH
 36H  25/0000Z 17.0N  64.5W   30 KT  35 MPH
 48H  25/1200Z 17.5N  67.1W   30 KT  35 MPH
 72H  26/1200Z 19.2N  72.0W   25 KT  30 MPH...INLAND
 96H  27/1200Z 21.0N  76.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  28/1200Z...DISSIPATED

$$
Forecaster Pasch
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