Tropical Storm IRENE

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TROPICAL DEPRESSION IRENE DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT MON AUG 08 2005
 
CONVECTION HAS PERSISTED TO THE EAST OF THE LOW LEVEL
CENTER THIS AFTERNOON... OFTEN EMANATING FROM THE CENTER ITSELF. 
HOWEVER... THE LOW LEVEL CENTER REMAINS EXPOSED DVORAK INTENSITY
ESTIMATES REMAIN T2.0/30 KT.  ALTHOUGH IT IS POSSIBLE THAT TROPICAL
STORM FORCE WINDS ARE REACHING THE SURFACE IN A LIMITED AREA WITHIN
THE SPARSE CONVECTION... IRENE IS MAINTAINED AS 30 KT DEPRESSION
FOR THIS ADVISORY.  THE SYSTEM IS STRUGGLING TO REORGANIZE WITHIN A
FAIRLY DRY AND STABLE ENVIRONMENT WITH MODERATE VERTICAL SHEAR. 
THESE CONDITIONS SHOULD BE SLOW TO CHANGE ALONG THE FORECAST
TRACK... AND ACCORDINGLY THE SHIPS GUIDANCE SHOWS GRADUAL
STRENGTHENING TO 45 KT BY 60 HOURS...CONTINUING ON TO 62 KT BY 120
HOURS.  HOWEVER... THE GFDL DISSIPATES THE SYSTEM WITHIN A COUPLE
OF DAYS.  THE OFFICIAL FORECAST WILL COMPROMISE AND REMAIN SIMILAR
TO THE PREVIOUS ADVISORY... SHOWING MODEST AND GRADUAL
STRENGTHENING.
 
WHEN THE CONVECTION REDEVELOPED THIS MORNING... THE LOW LEVEL CENTER
SLOWED DOWN IN RESPONSE.  SMOOTHING THROUGH THE STOP-AND-GO MOTION
DURING THE PAST 12 HOURS OR SO YIELDS AN INITIAL MOTION OF 285/10. 
THE NEW OFFICIAL FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS
ADVISORY... AND THERE IS A LITTLE MORE CONFIDENCE IN THIS TRACK NOW
SINCE SOME OF THE MODELS THAT WERE EASTERN OUTLIERS THIS MORNING...
SUCH AS THE UKMET AND NOGAPS... HAVE SHIFTED WESTWARD. 
THEREFORE... MODELS ARE COMING INTO BETTER AGREEMENT THAT A SYSTEM
OF MODERATE TROPICAL STORM STRENGTH WILL MOVE WEST-NORTHWESTWARD
ALONG THE SOUTHERN PERIPHERY OF THE LOWER/MID LEVEL SUBTROPICAL
RIDGE.  THE SLOW MOTION SHOWN AT THE END OF THE OFFICIAL FORECAST
IS INDICATIVE OF THE GREAT UNCERTAINTY LATE IN THE PERIOD...WHEN
THE SPREAD IN THE MODELS IS STILL QUITE SIGNIFICANT.
 
FORECASTER KNABB
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      08/2100Z 22.5N  51.5W    30 KT
 12HR VT     09/0600Z 23.0N  53.1W    30 KT
 24HR VT     09/1800Z 23.6N  55.4W    35 KT
 36HR VT     10/0600Z 24.3N  57.8W    35 KT
 48HR VT     10/1800Z 25.1N  59.7W    40 KT
 72HR VT     11/1800Z 27.0N  63.5W    40 KT
 96HR VT     12/1800Z 29.5N  66.5W    45 KT
120HR VT     13/1800Z 31.5N  67.0W    45 KT
 
 
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