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Tropical Storm ANA


ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ANA DISCUSSION NUMBER  14
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022009
1100 AM AST SAT AUG 15 2009

MORNING SATELLITE IMAGERY SHOWS THAT THE CENTER OF ANA HAS BECOME
EXPOSED TO THE WEST OF THE CENTRAL CONVECTIVE AREA...SUGGESTING
SOME WESTERLY VERTICAL WIND SHEAR HAS DEVELOPED.  SATELLITE
INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN 35 KT...AND THAT
REMAINS THE INITIAL INTENSITY.

THE EXPOSED CENTER IS A LITTLE SOUTH OF THE PREVIOUS ADVISORY
POSITION...AND THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 270/14. 
OVERALL...A LOW/MID-LEVEL RIDGE SHOULD STEER ANA QUICKLY WEST-
NORTHWESTWARD...WITH ALL THE TRACK GUIDANCE AGREEING WITH THIS
SCENARIO.  HOWEVER...THERE IS A SIGNIFICANT SPREAD IN THE 120 HR
FORECAST POINTS.  THE ECMWF AND BAMS ARE AT THE NORTHERN EXTREME...
FORECASTING ANA TO BE OVER OR NEAR THE FLORIDA PENINSULA AT 120 HR. 
AT THE OTHER EXTREME ARE THE GFDL AND GFDN...WHICH FORECAST ANA TO
PASS SOUTH OF HISPANIOLA AND BE OVER THE NORTHWESTERN CARIBBEAN AT
120 HR.  THE NEW FORECAST TRACK IS SHIFTED A BIT TO THE SOUTH AND
WEST OF THE PREVIOUS TRACK IN BEST AGREEMENT WITH THE NOGAPS AND
THE HWRF.  HOWEVER...THE NEW TRACK IS STILL ON THE NORTHERN SIDE OF
THE GUIDANCE ENVELOPE AND NORTH OF THE CONSENSUS MODELS.

THE CURRENT SHEAR WAS NOT WELL FORECAST BY THE LARGE-SCALE
MODELS...AND IT IS UNCLEAR WHETHER THIS IS A TEMPORARY TREND OR A
SIGN OF LONG-TERM TROUBLE FOR ANA.  THE LARGE-SCALE MODELS SUGGEST
THAT LIGHT TO MODERATE SHEAR COULD AFFECT ANA EARLY AND LATE IN THE
FORECAST PERIOD...WITH THE LIGHTEST SHEAR NEAR THE 72 HR TIME. 
BASED ON THIS AND THE INCREASINGLY WARM WATER UNDER THE STORM...
MOST INTENSITY GUIDANCE FORECASTS ANA TO BECOME A HURRICANE.  ON
THE OTHER HAND...THE G-IV MISSION LAST NIGHT SUGGESTED THAT THE
CIRCULATION OF ANA LACKED VERTICAL DEPTH...ENDING AT ABOUT 500 MB. 
ADDITIONALLY...THE CYCLONE IS SURROUNDED BY DRY AIR IN WATER VAPOR
IMAGERY...AND MAY INTERACT WITH THE ISLAND OF HISPANIOLA IN 72 HR. 
BASED ON THIS...THE INTENSITY FORECAST CALLS FOR A PEAK INTENSITY
OF 60 KT...BELOW MOST OF THE GUIDANCE.  THIS INTENSITY FORECAST HAS
GREATER THAN NORMAL UNCERTAINTY.
 
A TROPICAL STORM WATCH MAY BE REQUIRED FOR PORTIONS OF THE LEEWARD
ISLANDS LATER TODAY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      15/1500Z 14.3N  48.3W    35 KT
 12HR VT     16/0000Z 14.6N  50.9W    40 KT
 24HR VT     16/1200Z 15.2N  54.4W    45 KT
 36HR VT     17/0000Z 16.1N  58.2W    50 KT
 48HR VT     17/1200Z 17.3N  62.0W    55 KT
 72HR VT     18/1200Z 19.5N  69.0W    60 KT
 96HR VT     19/1200Z 22.0N  74.5W    60 KT
120HR VT     20/1200Z 25.0N  80.0W    60 KT
 
$$
FORECASTER BEVEN
 
NNNN


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Page last modified: Thursday, 31-Dec-2009 12:09:03 UTC