WTPA42 PHFO 240853 TCDCP2 HURRICANE IOKE DISCUSSION NUMBER 18 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP012006 1100 PM HST WED AUG 23 2006 IOKE HAS BEEN INTENSIFYING THIS EVENING. INFRARED IMAGERY INDICATES THE EYE IS BECOMING WELL DEFINED AND THE CDO IS BECOMING MORE SYMMETRIC AROUND THE CENTER. THE T-NUMBERS FROM HFO...SAB...AND AFWA HAVE ALL INCREASED TO T5.5 AND JTWC HAS MAINTAINED A T5.0. THE INTENSITY HAS BEEN RAISED TO 100 KT FOR THIS ADVISORY...BRINGING IOKE BACK TO MAJOR HURRICANE STATUS /CATEGORY 3 ON THE SAFFIR- SIMPSON SCALE/ ONCE AGAIN. THE HURRICANE HAS BEEN MOVING NEAR 305/7 FOR THE PAST SIX HOURS... ALTHOUGH MORE RECENTLY THE MOTION APPEARS A BIT CLOSER TO DUE WEST. THE LONGWAVE TROUGH JUST WEST OF THE DATELINE HAS BEEN RETROGRADING WESTWARD...AND STRENGTHENING DEEP LAYER RIDGING NORTH OF THE CYCLONE IS EXPECTED TO CONTINUE STEERING IOKE ON A WEST-NORTHWEST COURSE THROUGH THE NEXT 24 TO 36 HOURS. THE MODELS...PARTICULARLY THE GFS...HAVE BEEN BACKING OFF ON THE INTENSIFICATION OF THE SUBTROPICAL RIDGE TO THE NORTHWEST AND WEST OF IOKE IN THE LATER TIME PERIODS...AND THE GUIDANCE CONSENSUS HAS TRENDED A BIT MORE NORTHWARD IN RESPONSE. THE OFFICIAL FORECAST ALSO FOLLOWS THIS TREND. CONDITIONS CONTINUE TO APPEAR FAVORABLE FOR MODEST INTENSIFICATION IN THE SHORT TERM. SEA SURFACE TEMPERATURES REMAIN WARM ALONG THE FORECAST TRACK. SHEAR IS EXPECTED TO BE NEGLIGIBLE UNDERNEATH STRONG UPPER LEVEL RIDGING...WHICH IS MOVING WESTWARD ROUGHLY IN TANDEM WITH THE CYCLONE. THE INTENSITY FORECAST BEYOND 36 HOURS BECOMES A BIT MORE CHALLENGING. THE MODELS INDICATE THAT THE WESTWARD MOVING UPPER RIDGE WILL START TO OUTRUN IOKE. AN UNSEASONABLY STRONG LONGWAVE TROUGH DIGGING SOUTHWARD BETWEEN THE MAIN HAWAIIAN ISLANDS AND IOKE IS EXPECTED TO INDUCE INCREASING NORTHERLY SHEAR AFTER 48 HOURS. HOWEVER...THE GLOBAL MODELS DIFFER IN THE AMOUNT OF SHEAR THAT IOKE WILL HAVE TO ENDURE...WITH THE GFS ON THE STRONGEST END OF THE GUIDANCE. THE FORECAST WEAKENING TREND IN THE LONGER RANGE REMAINS MORE MODEST THAN INDICATED BY THE SHIPS GUIDANCE AND MAINTAINS THAT IOKE WILL CROSS THE DATELINE INTO A THE WEST PACIFIC IN ABOUT 72 HOURS AS A TYPHOON. NOTE THAT NAMED TROPICAL CYCLONES CROSSING INTO THE WEST PACIFIC BASIN MAINTAIN THEIR ORIGINAL NAME. FORECAST POSITIONS AND MAX WINDS INITIAL 24/0900Z 18.6N 172.3W 100 KT 12HR VT 24/1800Z 19.0N 173.3W 100 KT 24HR VT 25/0600Z 19.4N 174.4W 105 KT 36HR VT 25/1800Z 19.6N 175.6W 105 KT 48HR VT 26/0600Z 19.6N 177.1W 100 KT 72HR VT 27/0600Z 19.1N 180.0E 90 KT 96HR VT 28/0600Z 18.7N 176.8E 85 KT 120HR VT 29/0600Z 18.5N 173.6E 70 KT $$ FORECASTER R BALLARD