ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM IRWIN DISCUSSION NUMBER 39 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 200 PM PDT SAT OCT 15 2011 THE LOW-LEVEL CENTER OF IRWIN BECAME EXPOSED TO THE NORTHEAST OF THE DEEP CONVECTION AROUND THE RELEASE OF THE PREVIOUS ADVISORY...AND IT HAS BECOME INCREASINGLY SEPARATED SINCE THAT TIME. THIS ASYMMETRIC CLOUD PATTERN IS DUE TO ABOUT 20 KT OF NORTHEASTERLY VERTICAL WIND SHEAR. THE INITIAL WIND SPEED IS HELD AT 35 KT...IN AGREEMENT WITH THE SATELLITE CLASSIFICATION FROM TAFB...BUT THIS COULD BE GENEROUS. IRWIN LIES OVER THE COOL WATER WAKE OF JOVA...AND SATELLITE DATA INDICATE THAT THE CENTER OF IRWIN IS CURRENTLY OVER WATERS OF ABOUT 23C. THESE COOL WATERS...STABLE AIR...AND AN INCREASE IN EASTERLY WIND SHEAR SHOULD CAUSE IRWIN TO WEAKEN SOME AND EVENTUALLY DEGENERATE TO A REMNANT LOW IN TWO TO THREE DAYS. THE OFFICIAL INTENSITY FORECAST IS UNCHANGED FROM EARLIER AND IS ON THE LOW SIDE OF THE GUIDANCE ENVELOPE...IN AGREEMENT WITH THE GFDL AND HWRF MODELS. IRWIN IS MOVING SOUTH-SOUTHWESTWARD AT ABOUT 8 KT. A TURN TO THE WEST IS FORECAST DURING THE NEXT 24 TO 36 HOURS AS A LOW- TO MID-LEVEL RIDGE BECOMES ORIENTED EAST-TO-WEST TO THE NORTH OF THE TROPICAL CYCLONE. IN 48 TO 72 HOURS...THE MODELS SUGGEST THAT IRWIN...OR ITS REMNANTS...COULD COME TO A HALT...PERHAPS REVERSING EASTWARD OR SOUTHEASTWARD AS IT BECOMES SHALLOW IN NATURE AND IS STEERED BY THE LOW-LEVEL FLOW. THE OFFICIAL FORECAST HAS BEEN ADJUSTED SOUTHWARD AND IS A LITTLE SLOWER THAN THE PREVIOUS ONE TO COME INTO BETTER AGREEMENT WITH THE LATEST GUIDANCE. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 15.6N 107.1W 35 KT 40 MPH 12H 16/0600Z 14.8N 107.7W 30 KT 35 MPH 24H 16/1800Z 14.3N 108.4W 30 KT 35 MPH 36H 17/0600Z 14.2N 109.4W 30 KT 35 MPH 48H 17/1800Z 14.1N 109.9W 30 KT 35 MPH 72H 18/1800Z 14.0N 110.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 19/1800Z 14.0N 110.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 20/1800Z...DISSIPATED $$ FORECASTER CANGIALOSI NNNN
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