000 WTPZ41 KNHC 162044 TCDEP1 TROPICAL STORM ALETTA DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012012 200 PM PDT WED MAY 16 2012 THE CONVECTIVE PATTERN OF THE CYCLONE HAS BECOME DISORGANIZED OVER THE PAST FEW HOURS...AND NOW CONSISTS OF A SHRINKING BALL OF DEEP CONVECTION NEAR THE CENTER AND A DISCONNECTED BAND TO THE EAST. THE LOW-LEVEL CENTER IS PARTIALLY EXPOSED ON THE SOUTHWESTERN EDGE OF THE MAIN CONVECTIVE MASS...INDICATIVE THAT SOUTHWESTERLY SHEAR MAY FINALLY BE TAKING A TOLL ON THE CYCLONE. ALTHOUGH DVORAK T-NUMBERS REMAIN AT 2.5 AT 1800 UTC...IT APPEARS AS IF A WEAKENING TREND MAY HAVE ALREADY BEGUN. THE INITIAL INTENSITY IS HELD AT 35 KT FOR THIS ADVISORY...ASSUMING THAT THE CYCLONE HAS WEAKENED A BIT SINCE A 1643 UTC ASCAT PASS SHOWED A COUPLE OF 40-KT VECTORS. THE GLOBAL MODELS SHOW MODERATE TO STRONG SOUTHWESTERLY SHEAR PERSISTING OVER THE NEXT SEVERAL DAYS...AS ALETTA MOVES INTO A REGION DOMINATED BY AN INCREASINGLY STABLE AND DRIER AIR MASS. THESE TWO SIGNIFICANT NEGATIVE FACTORS SHOULD HASTEN THE DEMISE OF THE CYCLONE...AND THE OFFICIAL NHC FORECAST NOW CALLS FOR ALETTA TO DEGENERATE INTO A REMNANT LOW IN ABOUT 48 HOURS. CENTER FIXES FROM SEVERAL MICROWAVE PASSES THIS MORNING AND RECENT VISIBLE SATELLITE IMAGES INDICATE THAT ALETTA HAS BEEN MAINTAINING A MORE WESTERLY MOTION...270/08...THAN INDICATED IN PREVIOUS ADVISORIES. UNDER THE EASTERN PERIPHERY OF A MID-LEVEL RIDGE... ALETTA SHOULD CONTINUE ON A GENERALLY WESTWARD TRACK FOR THE NEXT 12 HOURS OR SO. THEREAFTER...THE LARGE-SCALE MODELS SHOW THE RIDGE NORTH OF THE STORM ERODING AS A WEAKNESS DEVELOPS SOUTH OF BAJA CALIFORNIA. THIS SHOULD CAUSE THE TRACK OF THE STORM TO TURN NORTHWARD WITHIN 36 HOURS WITH A DECREASE IN FORWARD SPEED. THEREAFTER...THE REMNANT CIRCULATION IS EXPECTED TO TURN TOWARD THE NORTHEAST AND THEN TOWARD THE EAST AS IT BECOME EMBEDDED IN ANOMALOUS LOW-LEVEL WESTERLY FLOW SOUTH OF MAINLAND MEXICO. THE OFFICIAL TRACK FORECAST IS CLOSE TO THE PREVIOUS ONE THROUGH 36 HOURS AND A BIT MORE EASTWARD/FASTER AT LATER FORECAST TIMES...IN LINE WITH THE LATEST GUIDANCE. THE WIND RADII WERE ADJUSTED INWARD BASED UPON THE EARLIER ASCAT PASS. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 11.4N 113.5W 35 KT 40 MPH 12H 17/0600Z 11.7N 114.4W 30 KT 35 MPH 24H 17/1800Z 12.4N 115.1W 30 KT 35 MPH 36H 18/0600Z 13.1N 115.0W 25 KT 30 MPH 48H 18/1800Z 13.6N 114.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 19/1800Z 14.0N 113.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 20/1800Z 14.0N 111.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 21/1800Z...DISSIPATED $$ FORECASTER KIMBERLAIN