Tropical Storm IRENE

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TROPICAL DEPRESSION IRENE DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
ISSUED BY THE HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
5 PM EDT TUE AUG 09 2005

VISIBLE SATELLITE IMAGERY THIS AFTERNOON INDICATES THAT IRENE
APPEARS TO BE UNDERGOING A METAMORPHOSIS.  THE CLOUD STRUCTURE
ASSOCIATED WITH THE TROPICAL CYCLONE IS GRADUALLY BECOMING MORE
SYMMETRIC...CIRRUS OUTFLOW EMANATING FROM IT IS MORE DIVERGENT
...AND THERE ARE OCCASIONAL SIGNS OF BANDING. COMPARED TO 24 HOURS
EARLIER...IRENE IS CERTAINLY BETTER ORGANIZED. ALL SATELLITE
AGENCIES EXCEPT AFWA ARRIVED AT DVORAK CLASSIFICATIONS BELOW
TROPICAL STORM STRENGTH.  ON THIS BASIS...IRENE IS KEPT A TROPICAL
DEPRESSION AT THIS TIME.

THERE WERE SOME DIFFERENCES CONCERNING THE INITIAL POSITION OF THE
DEPRESSION...BUT POSITION ESTIMATES YIELD A SIX HOUR MOTION OF
280/8.  IN THE SHORT TERM...IRENE MAY NOT REGAIN ENOUGH
ORGANIZATION TO BE VERTICALLY COUPLED.  THUS IT WILL LIKELY ASSUME
A HEADING AND SPEED MORE COMPARABLE WITH THE LOWER LEVEL FLOW. 
THEREAFTER...THE FORECAST BECOMES MORE PROBLEMATIC. OVER THE NEXT
FEW DAYS...THE 12Z ECWMF AND NOGAPS MODELS INDICATE THAT IRENE WILL
MOVE UNDERNEATH A MID LEVEL RIDGE LYING OVER THE WESTERN ATLANTIC
...WHICH SHOULD KEEP THE STORM ON A MORE WESTERLY TRACK.  ON THE
OTHER HAND...THE 12Z UKMET SHOWS A SHORTWAVE TROF ERODING THE RIDGE
ENOUGH TO CAUSE A TURN TOWARD THE NORTH AROUND 72 HOURS. 

THE FUTURE TRACK OF IRENE DEPENDS VERY MUCH ON THE EVOLVING LONGWAVE
PATTERN IN THE MID LATITUDES LATER ON IN THE FORECAST. 
SPECIFICALLY...A BLOCKING RIDGE OVER ALASKA AND AN AMPLIFICATION OF
A DOWNSTREAM TROF OVER THE NORTH CENTRAL/NORTHWESTERN U.S. WILL
DETERMINE HOW ROBUST THE WESTERN ATLANTIC RIDGE WILL BE AND HOW
LONG IT STAYS IN PLACE.  AT THIS TIME...GIVEN THE GOOD AGREEMENT ON
THE LONGWAVE PATTERN IN THE NCEP AND ECWMF ENSEMBLE MEAN SOLUTIONS
WHICH DEPICT A CLOSED ANTICYCLONE TO FORM OVER THE WESTERN ATLANTIC
AT THAT RANGE...THE TRACK OF IRENE HAS BEEN SHIFTED FARTHER SOUTH
AND WEST.

AFTER SEVERAL DAYS OF ENDURING MODERATE VERTICAL WIND SHEAR IN
ASSOCIATION WITH A SHARP UPPER TROF TO ITS NORTHEAST...MODELS
GENERALLY AGREE THAT IRENE WILL ENTER A MORE FAVORABLE ENVIRONMENT
FOR DEVELOPMENT.  THEY FORECAST THE SHEAR VECTOR OVER THE
DEPRESSION TO SHIFT FROM A NORTHWESTERLY TO EAST AND BECOME WEAKER
WITHIN 24 TO 36 HOURS. AFTER THIS TIME...IRENES POSITION SOUTH OF
THE RIDGE OVER THE WESTERN ATLANTIC SHOULD FAVOR A GENERAL
INTENSIFICATION.  THE FORECAST INTENSIFICATION IS VERY MUCH IN LINE
WITH THE SHIPS MODEL THROUGH THE PERIOD.

 
FORECASTER KIMBERLAIN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/2100Z 22.6N  54.4W    30 KT
 12HR VT     10/0600Z 22.7N  55.7W    30 KT
 24HR VT     10/1800Z 23.4N  57.7W    35 KT
 36HR VT     11/0600Z 24.7N  59.5W    40 KT
 48HR VT     11/1800Z 25.7N  60.5W    45 KT
 72HR VT     12/1800Z 27.0N  62.6W    50 KT
 96HR VT     13/1800Z 28.0N  65.4W    55 KT
120HR VT     14/1800Z 29.0N  68.5W    60 KT
 
 
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