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Tropical Storm ALETTA Forecast Discussion Number 5

Issued at 800 AM PDT TUE MAY 15 2012

000
WTPZ41 KNHC 151448
TCDEP1
 
TROPICAL STORM ALETTA DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP012012
800 AM PDT TUE MAY 15 2012
 
THE CLOUD PATTERN OF ALETTA HAS CHANGED LITTLE DURING THE PAST 12
HOURS OR SO. THE CYCLONE CONSISTS OF A COUPLE OF CLUSTERS OF DEEP
CONVECTION WITH THE CENTER APPARENTLY ON THE SOUTHEASTERN EDGE OF
THE MAIN CONVECTIVE MASS.  DVORAK T-NUMBERS REMAIN AT 2.5 FROM BOTH
SAB AND TAFB AND THE INITIAL INTENSITY IS ONCE AGAIN MAINTAINED AT
35 KT.  ALETTA IS EXPECTED TO REMAIN IN A LOW SHEAR ENVIRONMENT AND
OVER WARM SSTS THAT COULD ALLOW FOR SOME SLIGHT STRENGTHENING
DURING THE 12 HOURS OR SO.  AFTER THAT TIME...AN APPROACHING
UPPER-LEVEL TROUGH FROM THE WEST IS EXPECTED TO CAUSE AN INCREASE
IN SOUTHWESTERLY SHEAR.  THE INCREASING SHEAR AND SOME DRIER AIR
THAT IS CURRENTLY LOCATED TO THE WEST OF THE CYCLONE ARE EXPECTED
TO INITIATE WEAKENING WITHIN 24-36 HOURS.  ALETTA IS FORECAST TO
DEGENERATE INTO A REMNANT LOW IN A FEW DAYS AND DISSIPATE BY THE
END OF THE FORECAST PERIOD.
 
ALETTA IS MOVING WESTWARD OR 280/8 KT.  THE CYCLONE SHOULD CONTINUE
MOVING WESTWARD TO WEST-NORTHWESTWARD WITH SOME INCREASE IN FORWARD
SPEED DURING THE NEXT 2-3 DAYS AS IT REMAINS SOUTH OF A STRONG
MID-LEVEL RIDGE.  THE RIDGE IS FORECAST TO WEAKEN LATER IN THE
FORECAST PERIOD AS A MID- TO UPPER-LEVEL TROUGH APPROACHES FROM
THE NORTHWEST.  THIS SHOULD RESULT IN A CONSIDERABLE SLOWING OF THE
FORWARD MOTION OF THE CYCLONE.  THE TRACK GUIDANCE IS IN FAIRLY
GOOD AGREEMENT THROUGH 48 HOURS...BUT THERE IS SOME SPREAD AFTER
THAT TIME AS SOME OF THE MODELS TURN THE CYCLONE NORTHWARD BY THE
END OF THE PERIOD.  FOR NOW...THE NHC FORECAST SHOWS ALLETTA
MAINTAINING A WEST-NORTHWESTWARD MOTION UNTIL DISSIPATION.
HOWEVER... THE UPDATED FORECAST IS CONSIDERABLY SLOWER THAN THE
PREVIOUS ADVISORY AT DAYS 3 AND 4...IN DEFERENCE TO THE SLOWER
FORWARD SPEED SHOWN BY MOST OF THE DYNAMICAL MODELS BY THAT TIME.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/1500Z 10.6N 109.6W   35 KT  40 MPH
 12H  16/0000Z 11.0N 111.1W   40 KT  45 MPH
 24H  16/1200Z 11.3N 113.2W   40 KT  45 MPH
 36H  17/0000Z 11.6N 115.3W   35 KT  40 MPH
 48H  17/1200Z 12.0N 117.0W   30 KT  35 MPH
 72H  18/1200Z 12.5N 119.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  19/1200Z 13.0N 120.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  20/1200Z...DISSIPATED
 
$$
FORECASTER BROWN
 

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