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BULLETIN
SUBTROPICAL STORM ANA ADVISORY NUMBER 1...CORRECTED
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM AST SUN APR 20 2003
CORRECTED TO ADD INTERMEDIATE ADVISORY IN LAST PARAGRAPH
...SECOND SUBTROPICAL CYCLONE OF RECORD IN APRIL FORMS TO THE
SOUTHWEST OF BERMUDA...
THE GOVERNMENT OF BERMUDA HAS ISSUED A TROPICAL STORM WARNING FOR
BERMUDA.
AT 11 PM AST...0300Z...THE CENTER OF SUBTROPICAL STORM ANA WAS
LOCATED NEAR LATITUDE 31.3 NORTH...LONGITUDE 66.0 WEST OR ABOUT
110 MILES...175 KM...SOUTHWEST OF BERMUDA.
ANA IS MOVING TOWARD THE EAST-SOUTHEAST NEAR 10 MPH...17 KM/HR...AND
THIS MOTION IS EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS.
MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH... 65 KM/HR...WITH HIGHER
GUSTS. SOME SLOW STRENGTHENING IS POSSIBLE DURING THE NEXT
24 HOURS.
WINDS OF 40 MPH EXTEND OUTWARD UP TO 70 MILES...110 KM FROM THE
CENTER. THESE WINDS COULD SPREAD OVER BERMUDA LATER TONIGHT AND
MONDAY.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1002 MB...29.59 INCHES.
REPEATING THE 11 PM AST POSITION...31.3 N... 66.0 W. MOVEMENT
TOWARD...EAST-SOUTHEAST NEAR 10 MPH. MAXIMUM SUSTAINED
WINDS... 40 MPH. MINIMUM CENTRAL PRESSURE...1002 MB.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR LOCAL WEATHER OFFICE.
AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 2 AM AST...MONDAY...FOLLOWED BY THE NEXT COMPLETE ADVISORY
AT 5 AM AST...MONDAY.
FORECASTER BEVEN
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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
Below is wheh NHC classified Ana as Tropical.
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TROPICAL STORM ANA DISCUSSION NUMBER 7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT TUE APR 22 2003
AT 09Z...A SHIP REPORTED 44 KT AT A POSITION ABOUT 50 N MI SOUTH OF
THE CENTER AND THE INITIAL WIND SPEED IS INCREASED TO 45 KT FOR THIS
ADVISORY. BASED ON THE PROXIMITY OF THE STRONGEST WINDS TO THE
CENTER OF THE CYCLONE AS WELL AS AMSU TEMPERATURE STRUCTURE DATA
WHICH SHOWS A SLIGHTLY WARM CORE NEAR THE SURFACE AND ALOFT...ANA IS
CHANGED FROM SUBTROPICAL TO TROPICAL STATUS.
CIMSS CLOUD MOTION VERTICAL WIND SHEAR IS ABOUT 30 KT OVER ANA AND
GUIDANCE MODELS SHOW THIS SHEAR PERSISTING THROUGH 72 HOURS. WILL
THE PRESENT SHEAR KILL THE STORM? THE SHIPS MODEL AND UKMET SHOW
DISSIPATION BY 72 HOURS WHILE THE GFS AND GFDL MODELS MAINTAIN A 40
TO 50 KT CIRCULATION THROUGH 72 HOURS. THE OFFICIAL FORECAST
MAINTAINS THE CYCLONE WITH SOME WEAKENING THROUGH 72 HOURS.
THE INITIAL MOTION IS 080/14. ANA IS EMBEDDED IN A WESTERLY CURRENT
AND IS FORECAST TO MOVE EAST TO EAST-NORTHEASTWARD FOR 72 HOURS IN
GENERAL AGREEMENT WITH THE GFS...GFDL...AND NOGAPS MODELS. THE
UKMET MODEL SHOWS A STRANGE TURN TOWARD THE SOUTH...THEN
DISSIPATION...IN 48 HOURS.
THE 34-KT WIND SPEED RADII AND 12-FT WAVE HEIGHT RADII ARE INCREASED
BASED ON SHIP REPORTS.
FORECASTER LAWRENCE
FORECAST POSITIONS AND MAX WINDS
INITIAL 22/1500Z 29.8N 57.5W 45 KTS
12HR VT 23/0000Z 30.5N 54.6W 45 KTS
24HR VT 23/1200Z 31.4N 51.2W 40 KTS
36HR VT 24/0000Z 31.9N 47.5W 40 KTS
48HR VT 24/1200Z 32.4N 45.0W 35 KTS
72HR VT 25/1200Z 32.0N 40.5W 30 KTS
It was a very interesting development of this system in 2003 that gave a very early start to that season.
Link to 2009 S2K numbers poll.
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