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Tropical Storm ALETTA (Text)

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TROPICAL STORM ALETTA DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP012006
200 PM PDT SAT MAY 27 2006
 
BANDING FEATURES HAVE CONTINUED TO IMPROVE AND DVORAK T-NUMBERS ARE A
CONSENSUS T2.5/35 KT FROM BOTH TAFB AND SAB USING A SHEAR PATTERN.
THUS...THE SYSTEM HAS BEEN NAMED TROPICAL STORM ALETTA. AN
IMPRESSIVE MID- TO UPPER-LEVEL CIRCULATION HAS BEEN NOTED IN BOTH
RADAR AND SATELLITE IMAGERY MOST OF THE DAY...BUT MID-LEVEL SHEAR
UNDERCUTTING THE OTHERWISE IMPROVING UPPER-LEVEL OUTFLOW PATTERN HAS
RESULTED IN THE LOW-LEVEL CIRCULATION CENTER BECOMING EXPOSED JUST
WEST OF THE STRONGEST CONVECTION.
 
THE BROAD CENTER OF ALETTA HAS REFORMED FARTHER TO THE NORTHEAST...
WHICH MAKES THE INITIAL MOTION ESTIMATE OF 040/03 KT SOMEWHAT
UNCERTAIN. IT APPEARS...HOWEVER... THAT ALETTA HAS MOVED NORTH OF
THE SUBTROPICAL RIDGE AXIS NOW...SO A GENERAL SLOW NORTHEASTWARD
MOTION IS EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS OR SO. AFTER
THAT...STEERING CURRENTS ARE FORECAST TO BECOME ILL-DEFINED. THE
LONE EXCEPTION IS THE NOGAPS MODEL WHICH CONTINUES TO INSIST THAT
ALETTA WILL CROSS MEXICO AND INTO THE BAY OF CAMPECHE. WHILE THE
MID- AND UPPER-LEVEL CIRCULATION MAY END UP DOING THAT...IT IS
HIGHLY UNLIKELY THAT THE LOW-LEVEL CIRCULATION COULD MAKE IT OVER
THE RATHER FORMIDABLE SIERRA MADRE MOUNTAIN RANGE. THE CONSENSUS OF
THE OTHER GLOBAL MODELS... INCLUDING THE GFDL MODEL... CALLS FOR
ALETTA TO MOVE NEAR AND POSSIBLY JUST INLAND ALONG THE SOUTH-CENTRAL
COAST OF MEXICO BY 48 HOURS...AND THEN TURN WESTWARD BACK OVER WATER
AS MID-LEVEL RIDGING BUILDS ACROSS CENTRAL MEXICO. THE OFFICIAL
FORECAST TRACK IS SIMILAR TO BUT A LITTLE EAST OF THE PREVIOUS TWO
TRACKS...AND IS CLOSE TO THE CONU CONSENSUS MODEL.
 
WHILE UPPER-LEVEL OUTFLOW HAS IMPROVED... WEST-SOUTHWESTERLY
MID-LEVEL SHEAR CONTINUES TO DISPLACE THE DEEP CONVECTION TO THE
EAST OF THE LOW-LEVEL CENTER. HOWEVER...ALL OF THE GLOBAL MODELS
AGREE THAT BY 36 HOURS...VERTICAL SHEAR IS EXPECTED TO DECREASE TO
LESS THAN 10 KT. THIS SHOULD ALLOW FOR AT LEAST SLOW STRENGTHENING
TO OCCUR UP UNTIL ALETTA NEARS LAND IN 36-48 HOURS. THE OFFICIAL
INTENSITY FORECAST IS CLOSE TO THE SHIPS MODEL THROUGH 24 HOURS...
AND THEN SLIGHTLY HIGHER THEREAFTER WHEN ALETTA IS EXPECTED TO MOVE
UNDERNEATH THE LARGE-SCALE 200 MB RIDGE AXIS. 
 
DUE TO THE UNCERTAINTY IN BOTH THE TRACK AND INTENSITY FORECASTS AT
...THE GOVERNMENT OF MEXICO HAS ISSUED A TROPICAL STORM WARNING FROM
PUNTA MALDONADO WESTWARD TO TECPAN DE GALEANA MEXICO.
 
FORECASTER STEWART
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/2100Z 15.6N 100.5W    35 KT
 12HR VT     28/0600Z 16.0N 100.2W    40 KT
 24HR VT     28/1800Z 16.3N  99.9W    45 KT
 36HR VT     29/0600Z 16.7N 100.3W    50 KT
 48HR VT     29/1800Z 16.9N 100.7W    50 KT
 72HR VT     30/1800Z 17.0N 101.5W    55 KT
 96HR VT     31/1800Z 16.8N 102.5W    55 KT
120HR VT     01/1800Z 16.5N 103.5W    55 KT
 
 
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