000 WTPZ41 KNHC 081500 TCDEP1 HURRICANE IRWIN DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 800 AM PDT SAT OCT 08 2011 THE MODERATE EASTERLY VERTICAL SHEAR PARTIALLY BEING INDUCED BY NEARBY TROPICAL STORM JOVA IS TAKING ITS TOLL ON IRWIN. THE LOW-LEVEL CENTER HAS EMERGED ON THE EAST SIDE OF THE DEEP CONVECTION AS SEEN IN THE FIRST GEOSTATIONARY VISIBLE IMAGERY. BOTH SUBJECTIVE AND ADVANCED DVORAK INTENSITY ESTIMATES HAVE DROPPED CONSIDERABLY WITH TAFB...SAB...AND CIMSS ADT INDICATING CURRENT-INTENSITY NUMBERS OF 4.5...4.0...AND 4.1...RESPECTIVELY. CIMSS AMSU EVEN SUGGESTS WELL-BELOW HURRICANE INTENSITY. THE INITIAL INTENSITY IS ESTIMATED TO BE 65 KT...WITH CONSIDERABLE UNCERTAINTY. THE HURRICANE IS CURRENTLY EMBEDDED IN A VERY WEAK STEERING FLOW AND INITIAL MOTION IS SET AT 345 DEGREES AT 2 KT. THE CYCLONE SHOULD START MOVING OFF TOWARD THE EAST WITH INCREASING FORWARD SPEED OVER THE NEXT FEW DAYS AS IT RESPONDS TO A SHORT-WAVE TROUGH DIGGING DOWN OVER THE SW UNITED STATES AND NE MEXICO. THE INFLUENCE ON THE STEERING BY NEARBY TROPICAL STORM JOVA IS MINIMAL CURRENTLY... THOUGH THE ECMWF MODEL SUGGESTS SOME FUIJIWHARA INTERACTION AFTER DAY TWO WITH IRWIN PUSHED TO A SOUTH-OF-EAST TRACK IN A MUTUAL COUNTER-CLOCKWISE ROTATION OF THE TWO VORTICES. THE FORECAST TRACK IS SIMILAR TO THE MULTI-MODEL CONSENSUS. THE FORECAST IS ALSO SLIGHTLY SOUTH THE PREVIOUS ADVISORY BECAUSE OF A MODEST RELOCATION OF THE VORTEX AT THE INITIAL TIME. THE INTENSITY FORECAST OF IRWIN IS QUITE DIFFICULT. THE EASY PART IS THAT THE SEA SURFACE TEMPERATURES UNDER THE TRACK OF THE CYCLONE SHOULD REMAIN A VERY WARM 28C. ALSO...THE VERTICAL SHEAR CURRENTLY PLAGUING THE CYCLONE SHOULD SOMEWHAT ABATE DURING THE NEXT DAY OR TWO...ALLOWING A MODERATE REBOUND IN THE INTENSITY TO OCCUR. HOWEVER...BY DAY THREE THE SHEAR MAY AGAIN INCREASE AT THE SAME TIME THAT THE ATMOSPHERE BECOMES MORE STABLE TO DEEP CONVECTION. UNFORTUNATELY...THE INTENSITY GUIDANCE SHOWS A VERY LARGE VARIABILITY AT THE EXTENDED RANGE...ANYWHERE FROM A WEAK TROPICAL STORM TO A CATEGORY 2 HURRICANE. THE INTENSITY FORECAST IS BETWEEN THE MULTI-MODEL CONSENSUS ON THE LOW SIDE AND THE PREVIOUS ADVISORY ON THE HIGH SIDE...AND HAS EVEN MORE UNCERTAINTY THAN USUAL. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 14.3N 121.0W 65 KT 75 MPH 12H 09/0000Z 14.6N 120.8W 65 KT 75 MPH 24H 09/1200Z 14.8N 120.3W 70 KT 80 MPH 36H 10/0000Z 15.0N 119.4W 75 KT 85 MPH 48H 10/1200Z 15.1N 118.0W 70 KT 80 MPH 72H 11/1200Z 15.0N 114.5W 65 KT 75 MPH 96H 12/1200Z 16.0N 110.5W 60 KT 70 MPH 120H 13/1200Z 19.0N 107.0W 55 KT 65 MPH $$ FORECASTER LANDSEA/STEWART