ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IRWIN DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 800 PM PDT SUN OCT 09 2011 DEEP CONVECTION ASSOCIATED WITH IRWIN HAS BEEN GRADUALLY DECREASING THIS EVENING...MUCH LIKE WHAT OCCURRED YESTERDAY AT THIS TIME. ASIDE FROM THE WEAKENING CONVECTION...MICROWAVE DATA INDICATE THAT THE OVERALL STRUCTURE HAS CHANGED LITTLE DURING THE LAST SEVERAL HOURS WITH THE LOW-LEVEL CENTER LOCATED TO THE NORTH OF A CURVED BAND. THE INITIAL WIND SPEED IS HELD AT 45 KT...BUT THIS COULD BE A LITTLE GENEROUS. THE TROPICAL STORM HAS NOW TURNED TO THE EAST AND IS MOVING A LITTLE FASTER...AND THE LATEST INITIAL MOTION ESTIMATE IS 085/5. AN EASTWARD OR PERHAPS EAST-SOUTHEASTWARD MOTION IS FORECAST DURING THE NEXT COUPLE OF DAYS AS THE CYCLONE MOVES IN THE FLOW TO THE EAST OF A SHARPENING TROUGH OR CUTOFF LOW TO THE SOUTHWEST OF THE BAJA PENINSULA. IRWIN IS THEN FORECAST TO TRACK JUST NORTH OF DUE EAST...BRINGING IT NEAR THE COAST OF SOUTHWESTERN MEXICO BY THE END OF THE FORECAST PERIOD. A SLOW DOWN IS FORECAST BY DAY 5...AS MANY OF THE GLOBAL MODELS SHOW A RIDGE BUILDING TO THE NORTH OF THE STORM BY THAT TIME. THE OFFICIAL TRACK FORECAST HAS BEEN ADJUSTED SOUTHWARD...ESPECIALLY AT DAYS FOUR AND FIVE...TO COME INTO BETTER AGREEMENT WITH THE LATEST GUIDANCE. IRWIN IS CURRENTLY IN A RELATIVELY LOW WIND SHEAR ENVIRONMENT AND OVER ABOUT 28C WATERS. HOWEVER...THE STORM STILL LIES NEAR STABLE AIR AND THAT COULD BE A REASON WHY IT HAS BEEN STRUGGLING TO STRENGTHEN RECENTLY. ALTHOUGH THE CYCLONE WILL BE MOVING INTO A MORE MOIST ENVIRONMENT LATER THIS WEEK...THE SHIPS MODEL SHOWS EASTERLY SHEAR INCREASING OVER IRWIN. MEANWHILE...THE FORECAST TRACK TAKES IRWIN OVER THE COOL WATER WAKE CREATED BY HURRICANE JOVA. THE INTENSITY MODELS ARE QUITE DIVERGENT WITH THE SHIPS/LGEM SHOWING A GRADUAL WEAKENING...AND THE GFDL/HWRF BRINGING IRWIN TO HURRICANE STRENGTH. GIVEN THE MIXED SIGNALS IN BOTH THE ENVIRONMENTAL FACTORS AND THE MODELS...THE OFFICIAL FORECAST SHOWS IRWIN REMAINING STEADY STATE THROUGHOUT THE PERIOD. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 15.2N 118.7W 45 KT 50 MPH 12H 10/1200Z 15.4N 117.6W 45 KT 50 MPH 24H 11/0000Z 15.4N 116.1W 45 KT 50 MPH 36H 11/1200Z 15.2N 114.5W 45 KT 50 MPH 48H 12/0000Z 15.1N 112.8W 45 KT 50 MPH 72H 13/0000Z 16.2N 108.5W 45 KT 50 MPH 96H 14/0000Z 17.0N 105.0W 45 KT 50 MPH 120H 15/0000Z 17.0N 103.5W 45 KT 50 MPH $$ FORECASTER CANGIALOSI NNNN
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