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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