ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM ALETTA DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP012006 800 AM PDT SUN MAY 28 2006 AN AQUA MICROWAVE PASS AT 0820Z AND A TRMM PASS AT 1111Z INDICATE THAT THE CENTER OF ALETTA DRIFTED WESTWARD OR SOUTHWESTWARD OVERNIGHT AWAY FROM THE DEEP CONVECTION...ALTHOUGH A NEW BURST HAS DEVELOPED JUST TO THE EAST OF THE CIRCULATION CENTER. DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB AT 12Z WERE 45 AND 35 KT...RESPECTIVELY...AND THE INITIAL INTENSITY WILL BE HELD AT 40 KT FOR THIS ADVISORY. THE INITIAL MOTION IS STATIONARY. STEERING CURRENTS ARE WEAK AND MODEL GUIDANCE IS DIVERGENT. A WEAK MID-LEVEL RIDGE OF HIGH PRESSURE OVER MEXICO IS CURRENTLY IMPEDING ALETTA'S PROGRESS TOWARD THE COAST...BUT SOME OF THE GLOBAL MODELS...INCLUDING THE NOGAPS AND ECMWF...SUGGEST THAT THIS RIDGE WILL WEAKEN AS A SHORT-WAVE TROUGH OFF THE BAJA PENINSULA MOVES EASTWARD. THIS COULD ALLOW ALETTA TO MOVE CLOSER TO THE COAST OVER THE NEXT DAY OR SO. ALTHOUGH THE GFDL TRACKER KEEPS ALETTA OFFSHORE...THE MODEL'S 850 MB VORTICITY CENTER CLEARLY MOVES INLAND EAST OF ACAPULCO IN ABOUT 30 HOURS. GIVEN THE UNCERTAINTIES...THERE ARE NO CHANGES TO THE WATCHES OR WARNINGS AT THIS TIME. AFTER 24-48 HOURS...MOST OF THE GLOBAL MODELS RESTRENGTHEN THE SUBTROPICAL RIDGE...AND SO THE OFFICIAL FORECAST SHOWS A SLOW WESTWARD MOTION THROUGH THE LATTER PORTION OF THE FORECAST PERIOD. ALETTA IS STILL EXPERIENCING MID- TO UPPER-LEVEL WESTERLY FLOW THAT HAS BEEN LIMITING DEVELOPMENT. SHOULD ALETTA REMAIN OFFSHORE AS FORECAST...THE GLOBAL MODELS SUGGEST A MORE FAVORABLE ANTICYCLONIC UPPER-LEVEL FLOW WITH LOWER SHEAR SHOULD EVOLVE OVER THE NEXT DAY OR TWO. CONSEQUENTLY...THE OFFICIAL FORECAST INDICATES SOME STRENGTHENING THAT IS IN GOOD AGREEMENT WITH THE SHIPS MODEL GUIDANCE. AS NOTED IN THE PREVIOUS DISCUSSION HOWEVER...DRY AIR JUST TO THE WEST OF ALETTA WOULD BE AN INHIBITING FACTOR. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 28/1500Z 15.5N 101.3W 40 KT 12HR VT 29/0000Z 15.6N 101.3W 40 KT 24HR VT 29/1200Z 15.9N 101.2W 45 KT 36HR VT 30/0000Z 16.2N 101.2W 50 KT 48HR VT 30/1200Z 16.5N 101.5W 55 KT 72HR VT 31/1200Z 16.5N 102.5W 55 KT 96HR VT 01/1200Z 16.5N 103.5W 55 KT 120HR VT 02/1200Z 16.0N 104.5W 55 KT $$ NNNN
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Page last modified: Monday, 11-Sep-2006 11:28:39 UTC