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Tropical Storm ANA


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SUBTROPICAL STORM ANA DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SUN APR 20 2003
 
THE PERSISTENT AREA OF LOW PRESSURE LOCATED BETWEEN BERMUDA AND THE 
EASTERN U.S. HAS SHOWN INCREASED ORGANIZED CONVECTION NEAR THE 
CENTER DURING THE PAST 24 HR.  SATELLITE INTENSITY ESTIMATES ARE 
SUBTROPICAL 35-40 KT FROM TAFB AND TROPICAL 35 KT FROM SAB.  AS THE 
CYCLONE IS UNDER A SIGNIFICANT UPPER-LEVEL TROUGH...THE SYSTEM WILL 
BE CALLED A SUBTROPICAL STORM RATHER THAN A TROPICAL STORM.  RECENT 
QUIKSCAT DATA SUPPORT THE ESTIMATES...INDICATING WIDESPREAD 30-40 KT 
WINDS WITHIN 60-75 NM OF THE CENTER AND PEAK WINDS AS HIGH AS 55 KT. 
THE STRONGER WINDS MAY BE OVERDONE DUE TO PRECIPITATION...SO THE 
INITIAL INTENSITY WILL BE SET TO A MORE CONSERVATIVE 35 KT.

THE INITIAL MOTION IS 110/9.  THE UPPER-LEVEL TROUGH THAT ANA IS 
EMBEDDED IN IN FORECAST TO MOVE EASTWARD.  ADDITIONALLY...THE
STORM IS SOUTHWEST OF A BAROCLINIC LOW NEAR 39N60W.  THIS 
COMBINATION SHOULD MOVE THE STORM ON A BASIC EAST-SOUTHEASTWARD TO 
EASTWARD TRACK.  GUIDANCE GENERALLY AGREES WITH THIS SCENARIO... 
ALTHOUGH THERE ARE SIGNIFICANT DIFFERENCES IN THE SPEED OF MOTION 
ALONG WITH SOME DIRECTIONAL SPREAD.  THE OFFICIAL FORECAST TRACK 
WILL TAKE THE STORM DOWN THE CENTER OF THE GUIDANCE ENVELOPE IN BEST 
AGREEMENT WITH THE GFS AND UKMET.

ANA IS ONLY THE SECOND KNOWN SUBTROPICAL OR TROPICAL CYCLONE TO FORM 
IN APRIL...WITH THE OTHER OCCURRING IN 1992.  THAT SYSTEM MET ITS 
DEMISE DUE TO STRONG VERTICAL SHEAR...AND ANA SHOULD DO LIKEWISE AS 
THE UPPER-LEVEL TROUGH OVER IT OPENS UP AND EXPOSES THE CYCLONE TO 
THE WESTERLIES.  THIS IS FORECAST BY ALL LARGE-SCALE MODELS...AND 
THE INTENSITY FORECAST THUS CALLS FOR ANA TO WEAKEN AFTER 24 HR.  
THERE IS ALSO A CHANCE THAT A COLD FRONT ASSOCIATED WITH THE 
BAROCLINIC LOW TO THE NORTHEAST MAY SWEEP INTO ANA AND DESTROY ITS 
TROPICAL CHARACTERISTICS.  THUS...THE FORECAST OF ANA SURVIVING TO 
72 HR MAY BE GENEROUS.

IT SHOULD BE NOTED THAT THE FORECAST/ADVISORY IS PROVIDED IN THE 
3-DAY FORECAST FORMAT OF 2002 RATHER THAN THE 5-DAY FORECAST FORMAT 
DEVELOPED FOR THE 2003 SEASON.
 
FORECASTER BEVEN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     21/0300Z 31.3N  66.0W    35 KTS
12HR VT     21/1200Z 30.8N  64.7W    40 KTS
24HR VT     22/0000Z 30.3N  62.5W    40 KTS
36HR VT     22/1200Z 30.0N  59.8W    35 KTS
48HR VT     23/0000Z 30.0N  56.5W    35 KTS
72HR VT     24/0000Z 30.5N  50.0W    25 KTS...DISSIPATING
 
 
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