ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IRWIN DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2 AM PDT SAT AUG 27 2005 THE CIRCULATION CENTER OF TROPICAL STORM IRWIN HAS BECOME RATHER DIFFICULT TO LOCATE THIS EVENING...REMAINING PARTIALLY EXPOSED TO THE NORTHEAST OF THE WEAKENING DEEP CONVECTION. A BLEND OF DVORAK SATELLITE CLASSIFICATIONS GIVES AN INITIAL INTENSITY OF 40 KT FOR THIS ADVISORY. DYNAMICAL MODELS...INCLUDING THE GFS-BASED SHIPS...SUGGEST A GRADUAL INCREASE IN SOUTHEASTERLY SHEAR BEYOND DAY 2. SINCE THE SEA SURFACE TEMPERATURES ARE EXPECTED TO REMAIN RELATIVELY WARM THROUGH THE FORECAST PERIOD...THE SHEAR APPEARS TO BE THE PRIMARY INHIBITOR FOR FURTHER INTENSIFICATION. THE CANADIAN/UKMET AND ECMWF EVEN INDICATE DISSIPATION IN 48 HOURS. THE OFFICIAL INTENSITY FORECAST CALLS FOR LITTLE CHANGE OVER THE NEXT 2 DAYS...TAKING INTO ACCOUNT POSSIBLE INTERMITTENT BURSTS OF CONVECTION NEAR THE CENTER...THEN A GRADUAL WEAKENING THROUGH THE REMAINDER OF THE PERIOD. HOWEVER...THE FORECAST COULD BE GENEROUS CONSIDERING THE AFOREMENTIONED DISSIPATION SCENARIO. THE INITIAL MOTION IS ESTIMATED AT 270/9. AN EAST TO WEST ORIENTED MID-LEVEL RIDGE TO THE NORTH OF THE TROPICAL CYCLONE SHOULD KEEP IRWIN ON A GENERALLY WESTWARD TRACK. THE OFFICIAL FORECAST FOLLOWS THE CONU CONSENSUS AND THE PREVIOUS ADVISORY THROUGH 72 HOURS...THEN CONTINUES WESTWARD AS A SHALLOW SYSTEM WITHIN THE LOW-LEVEL FLOW. FORECASTER ROBERTS/KNABB FORECAST POSITIONS AND MAX WINDS INITIAL 27/0900Z 17.5N 111.9W 40 KT 12HR VT 27/1800Z 17.5N 113.3W 40 KT 24HR VT 28/0600Z 17.5N 115.2W 40 KT 36HR VT 28/1800Z 17.5N 116.8W 40 KT 48HR VT 29/0600Z 17.5N 118.5W 40 KT 72HR VT 30/0600Z 17.5N 122.0W 35 KT 96HR VT 31/0600Z 17.5N 125.5W 25 KT...DISSIPATING 120HR VT 01/0600Z 17.5N 129.0W 20 KT...REMNANT LOW $$ NNNN
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Page last modified: Saturday, 27-Aug-2005 09:10:15 UTC