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Tropical Storm ALETTA Forecast Discussion Number 4

Issued at 200 AM PDT TUE MAY 15 2012

000
WTPZ41 KNHC 150831
TCDEP1
 
TROPICAL STORM ALETTA DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP012012
200 AM PDT TUE MAY 15 2012
 
CONVENTIONAL AND MICROWAVE IMAGERY SHOW THAT ALETTA'S CLOUD PATTERN
HAS CHANGED LITTLE THIS EVENING...WITH THE CENTER OF CIRCULATION
EMBEDDED JUST WITHIN THE COLD CONVECTIVE OVERCAST.  UW-CIMSS
UPPER-LEVEL WV/IR WIND ANALYSIS INDICATES THAT ALETTA IS SITUATED
JUST SOUTH OF AN UPPER-LEVEL RIDGE AXIS WHICH IS CREATING A
DIFFLUENT PATTERN OVER THE NORTHWEST QUADRANT.  ENHANCED BD-CURVE
SATELLITE IMAGES REVEAL THAT THE COLDEST CLOUD TOPS RESIDE IN THIS
PARTICULAR QUADRANT.  SUBJECTIVE DVORAK SATELLITE CLASSIFICATIONS
ARE T2.5 FROM BOTH TAFB AND SAB AND THE INITIAL INTENSITY IS HELD
AT 35 KT FOR THIS ADVISORY. INTENSITY GUIDANCE CONTINUES TO
INDICATE ONLY MODEST STRENGTHENING THROUGH 24 HOURS BEFORE
INCREASING SOUTHWESTERLY VERTICAL SHEAR BEGINS TO IMPEDE ANY
FURTHER DEVELOPMENT.  THE OFFICIAL INTENSITY FORECAST IS A
COMPROMISE OF THE LGEM AND SHIPS MODELS...SUGGESTING GRADUAL
WEAKENING BEYOND THE 48 HOUR PERIOD AND DISSIPATION BY DAY 5.

THE INITIAL MOTION ESTIMATE IS 290/8...WITHIN THE DEEP EASTERLY
STEERING FLOW PRODUCED BY A MID-LEVEL RIDGE ANCHORED TO THE
NORTHWEST OF THE TROPICAL CYCLONE.  LITTLE CHANGE IN MOTION AND
FORWARD SPEED IS EXPECTED DURING THE NEXT 2 DAYS...AS DEPICTED BY
A MAJORITY OF THE GLOBAL MODELS.  AFTERWARD...A REDUCTION IN SPEED
IS FORECAST AS THE RIDGE AND ASSOCIATED STEERING CURRENT WEAKEN IN
RESPONSE TO AN APPROACHING MID TO UPPER-LEVEL TROUGH FROM THE
NORTHWEST.  THE NHC FORECAST IS BASICALLY A REPRODUCTION OF THE
PREVIOUS ADVISORY AND IS BASED ON A BLEND OF THE GFS...ECMWF...AND
THE FSSE SUPERENSEMBLE. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/0900Z 10.8N 108.7W   35 KT  40 MPH
 12H  15/1800Z 11.1N 110.1W   40 KT  45 MPH
 24H  16/0600Z 11.4N 112.2W   45 KT  50 MPH
 36H  16/1800Z 11.6N 114.3W   40 KT  45 MPH
 48H  17/0600Z 11.9N 116.2W   40 KT  45 MPH
 72H  18/0600Z 12.5N 119.0W   30 KT  35 MPH
 96H  19/0600Z 13.0N 121.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  20/0600Z...DISSIPATED
 
$$
FORECASTER ROBERTS
 

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