Tropical Storm ANA

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TROPICAL STORM ANA DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022009
500 PM AST SAT AUG 15 2009
 
THE CENTER OF ANA CONTINUES TO BE EXPOSED TO THE WEST OF THE
CONVECTION BY MODERATE VERTICAL WIND SHEAR.  THE UPPER-LEVEL WINDS
NEAR ANA ARE CURRENTLY LIGHT AND SOUTHERLY...MOST OF THE
CONTRIBUTION TO THE SHEAR SEEMS TO BE FROM THE FAST LOW-LEVEL FLOW
THE CENTER IS EMBEDDED IN.  SATELLITE INTENSITY ESTIMATES FROM TAFB
AND SAB REMAIN 35 KT...AND THAT REMAINS THE INITIAL INTENSITY.
 
THE INITIAL MOTION IS 270/15.  OVERALL...A LOW/MID-LEVEL RIDGE
SHOULD STEER ANA QUICKLY WESTWARD TO WEST-NORTHWESTWARD...WITH ALL
THE TRACK GUIDANCE AGREEING WITH THIS SCENARIO.  HOWEVER...THERE
REMAINS A SIGNIFICANT SPREAD IN THE 120 HR FORECAST POINTS.  THE
ECMWF AND BAMS ARE AT THE NORTHERN EXTREME...FORECASTING ANA TO
PASS OVER OR NEAR THE SOUTHERN FLORIDA PENINSULA BY 120 HR.
AT THE OTHER EXTREME ARE THE UKMET...GFDN...AND BAMM...WHICH
FORECAST ANA TO PASS SOUTH OF HISPANIOLA AND BE OVER THE
NORTHWESTERN CARIBBEAN AT 120 HR.  THE NEW FORECAST TRACK IS AGAIN
SHIFTED SOUTHWARD FROM THE PREVIOUS TRACK IN BEST AGREEMENT WITH
THE NOGAPS.  HOWEVER...THE NEW TRACK IS STILL ON THE NORTHERN SIDE
OF THE GUIDANCE ENVELOPE AND NOTABLY NORTH OF THE CONSENSUS MODELS.
 
IT IS UNCLEAR WHETHER THE CURRENT SHEAR IS A TEMPORARY TREND OR A
SIGN OF LONG-TERM TROUBLE FOR ANA.  THE LARGE-SCALE MODELS SUGGEST
THE FORMER IS THE CASE...AND SO THE INTENSITY FORECAST CONTINUES TO
CALL FOR STRENGTHENING.  HOWEVER...THE CYCLONE IS STILL SURROUNDED
BY DRY AIR IN WATER VAPOR IMAGERY...AND THE NEW FORECAST TRACK NOW
CALLS FOR THE SYSTEM TO MAKE LANDFALL ON HISPANIOLA...AN OCCURRENCE
THAT HAS DESTROYED STORMS MUCH STRONGER THAN ANA.  THE INTENSITY
FORECAST ASSUMES THAT THE CIRCULATION WILL SURVIVE THIS PASSAGE AND
INTENSIFY OVER THE WATERS NORTH OF CUBA.  AS BEFORE...THIS
INTENSITY FORECAST HAS GREATER THAN NORMAL UNCERTAINTY.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      15/2100Z 14.4N  50.0W    35 KT
 12HR VT     16/0600Z 14.7N  52.5W    35 KT
 24HR VT     16/1800Z 15.4N  56.0W    40 KT
 36HR VT     17/0600Z 16.1N  59.5W    45 KT
 48HR VT     17/1800Z 17.2N  63.2W    50 KT
 72HR VT     18/1800Z 19.0N  70.0W    50 KT...INLAND
 96HR VT     19/1800Z 21.5N  76.0W    55 KT...OVER WATER
120HR VT     20/1800Z 24.5N  82.0W    60 KT
 
$$
FORECASTER BEVEN
 
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