ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM 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 NNNN
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Page last modified: Monday, 31-Dec-2012 12:10:03 UTC