WTPA42 PHFO 251500 TCDCP2 TROPICAL STORM NEKI DISCUSSION NUMBER 28 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP032009 500 AM HST SUN OCT 25 2009 THE LOW-LEVEL CIRCULATION OF NEKI APPEARS TO BE DECOUPLING FROM ITS ASSOCIATED DEEP CONVECTION. THE CUMULONIMBUS CLOUDS...WHICH HAD BEEN RATHER PERSISTENT LAST EVENING...ARE NOW PULSING THIS MORNING. THESE SIGNS OF A LESS HEALTHY TROPICAL CYCLONE ARE UNDERSTANDABLE WHEN CONSIDERING THE LATEST UW/CIMSS ESTIMATE OF ENVIRONMENTAL VERTICAL WIND SHEAR IN THE VICINITY OF NEKI IS NOW A STRONG 31 KT FROM DUE WEST. THESE HOSTILE ENVIRONMENTAL CONDITIONS ARE MAINLY THE RESULT OF A LARGE UPPER TROPOSPHERIC TROUGH LOCATED JUST WEST NORTHWEST OF NEKI. A 1023 MB SURFACE HIGH IS LOCATED NEAR 38N 165W...OR ABOUT 825 NM NORTH OF NEKI. THE PRESENCE OF THIS ANTICYCLONE...WHICH IS MOVING RAPIDLY TOWARD THE NORTHEAST...HAS DISRUPTED NEKI/S NORTHWARD MOTION SINCE SATURDAY AFTERNOON. AT THE SAME TIME...THE DECOUPLING OF THE LOW LEVEL CENTER DUE TO THE STRONG SHEAR ALLOWED THE SURFACE SIGNATURE OF NEKI TO BEGIN DRIFTING TOWARD THE WEST LAST NIGHT. THIS SLOW WESTWARD DRIFT WAS ALSO SUGGESTED IN THE LATEST POSITION ESTIMATES PROVIDED BY THE SATELLITE ANALYSTS AT SAB...PHFO AND JTWC. IT ALSO APPEARS THAT NEKI MAY HAVE COMPLETED A SMALL ANTICYCLONIC LOOP SATURDAY NIGHT. FOR THIS ADVISORY...HAVE INDICATED NEKI/S CURRENT MOTION IS 290 DEGREES AT 5 KT. THE CURRENT INTENSITY ESTIMATES FROM THE SAME FIX AGENCIES RANGED FROM 2.5 TO 3.0. DUE TO THESE INTENSITY ESTIMATES AND THE OBVIOUS DETERIORATION OF THE TROPICAL STORM IN SATELLITE IMAGERY...HAVE WEAKENED NEKI TO 45 KT FOR THE INITIAL INTENSITY IN THIS ADVISORY. AFTER THE SURFACE HIGH FAR NORTH OF NEKI SLIPS RAPIDLY AWAY TO THE NORTHEAST LATER TODAY...THE INDIVIDUAL AND CONSENSUS TRACK GUIDANCE CONTINUE TO SHOW THE SYSTEM WILL BEGIN TO MOVE SLOWLY TOWARD THE NORTH NORTHWEST BY EARLY THIS AFTERNOON. THE GUIDANCE THEN MOVES NEKI AT A SLIGHTLY FASTER FORWARD SPEED TOWARD THE NORTH LATER TONIGHT. AT THE SAME TIME...NEKI IS FORECAST TO CONTINUE MOVING OVER COOLER SEA SURFACE TEMPERATURES AND LOWER OCEAN HEAT CONTENT VALUES TODAY AND TONIGHT. THE COOLING TREND OF THE UNDERLYING OCEAN COMBINED WITH STRONG VERTICAL WIND SHEAR CONTINUES TO SUPPORT ADDITIONAL WEAKENING LATER TODAY AND TONIGHT. AS IN THE PREVIOUS FORECAST...AN EXTRATROPICAL TRANSITION IS EXPECTED TO BEGIN BY MID-DAY MONDAY WHEN A LARGE AMPLITUDE UPPER LEVEL TROUGH AND A STRONG SURFACE FRONT BEGIN TO INTERACT WITH NEKI. THESE FEATURES WILL LIKELY CAUSE NEKI TO BEGIN ACCELERATING RAPIDLY TOWARD THE NORTH NORTHEAST BY MONDAY AFTERNOON. A COMPLETE TRANSITION TO AN EXTRATROPICAL GALE LOW IS EXPECTED BY LATE MONDAY NIGHT. NOTE...DO NOT BE SURPRISED IF NEKI IS COMPLETELY SHEARED BEYOND RECOGNITION...AS THE GFS AND ECMWF MODELS INDICATE...MONDAY NIGHT WHEN IT ENCOUNTERS THE STRONG WESTERLIES AND IS ABSORBED BY THE MID-LATITUDE SYSTEM OVER THE NORTH CENTRAL PACIFIC OCEAN. FORECAST POSITIONS AND MAX WINDS INITIAL 25/1500Z 24.8N 164.6W 45 KT 12HR VT 26/0000Z 25.7N 165.0W 40 KT 24HR VT 26/1200Z 27.5N 165.2W 35 KT 36HR VT 27/0000Z 30.9N 164.3W 35 KT...BECOMING EXTRATROPICAL 48HR VT 27/1200Z 37.2N 161.0W 35 KT...EXTRATROPICAL $$ FORECASTER HOUSTON