WTPA42 PHFO 210311 TCDCP2 HURRICANE NEKI DISCUSSION NUMBER 10 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP032009 500 PM HST TUE OCT 20 2009 NEKI STRENGTHENED INTO A HURRICANE DURING THE DAY AS A WELL-DEFINED BAND OF DEEP CONVECTION WRAPPED AROUND THE LOW LEVEL CENTER AND FORMED A RAGGED EYE. FIXES FROM PHFO...SAB...AND JTWC ALL CAME IN AT A 4.0...AND CIMSS ADT CALCULATED A CI OF 4.1. THUS...THE INITIAL INTENSITY IS SET AT 65 KT. NEKI IS MOVING TO THE NORTHWEST...320/13...TOWARD A WEAKNESS IN THE SUBTROPICAL RIDGE. MID LATITUDE WEATHER SYSTEMS MOVING WITHIN A BROAD NORTH PACIFIC JET STREAM BETWEEN 30N AND 40N WILL CONTINUE TO ERODE RIDGING AT THE SURFACE AND ALOFT THAT RUNS ROUGHLY ALONG 25N TO THE NORTH OF NEKI. AS A RESULT...NEKI WILL GRADUALLY TURN TO THE NORTH-NORTHWEST OVER THE NEXT 72 HOURS. THE GUIDANCE SHOWS THIS GENERAL TURN TO THE NORTH-NORTHWEST BUT STEADILY DIVERGES THROUGH TIME. THROUGH 72 HOURS...THE TRACK HAS BEEN NUDGED SLIGHTLY TO THE RIGHT...PUTTING IT ROUGHLY DOWN THE MIDDLE OF THE GUIDANCE CONSENSUS BUT SLIGHTLY LEFT OF THE TVCN...HWRF...AND GFDL. WITH CONFIDENCE BUILDING THAT NEKI WILL PASS EAST OF JOHNSTON ISLAND...THE HURRICANE WATCH FOR THAT ISLAND HAS BEEN CHANGED TO A TROPICAL STORM WATCH. NEKI IS FORECAST TO CONTINUE INTENSIFYING OVER THE NEXT 48 HOURS. SST VALUES WILL REMAIN IN THE 27 TO 28 DEGREE RANGE WITH LITTLE VERTICAL WIND SHEAR. AN ANTICYCLONE SITTING OVER THE MAIN HAWAIIAN ISLANDS AND THE BROAD UPPER TROUGHING TO NORTH WILL CONTINUE TO PROVIDE AN OUTFLOW CHANNEL SUPPORTING FURTHER INTENSIFICATION. BY 72 HOURS...THIS OUTFLOW CHANNEL WILL BREAK DOWN AND INTENSIFICATION IS EXPECTED TO CEASE AS NEKI APPROACHES THE AREA OF TROUGHING ALOFT. THE PEAK INTENSITY OF NEKI HAS BEEN HELD BACK SLIGHTLY TO BE IN BETTER AGREEMENT WITH THE HWRF...WHICH SHOWS A SIMILAR INTENSITY TREND AS THE FORECAST. BEYOND 72 HOURS...NEKI IS FORECAST TO ENTER A REGION OF WEAK STEERING AND MARGINAL ATMOSPHERIC CONDITIONS WHERE THE SPREAD OF THE TRACK GUIDANCE BECOMES CONSIDERABLE. THE MAIN QUESTION REMAINS WHETHER OR NOT A SURFACE HIGH WILL BUILD TO THE NORTH AND STEER NEKI ON A WESTWARD TRACK. THE CONSENSUS MODELS...GFS...HRWF...AND GFDL ARE SUGGESTING THAT PERSISTENT SURFACE TROUGHING WILL INHIBIT THE DEVELOPMENT OF THE RIDGE. THUS...THE WESTWARD TURN HAS BEEN ELIMINATED IN FAVOR OF A SLOW NORTHWARD MOTION AND GRADUAL WEAKENING. IT IS IMPORTANT TO NOTE THAT DURING THE WEEKEND NEKI IS FORECAST TO BE CLOSE TO THE EASTERN PORTION OF THE PAPAHANAUMOKUAKEA NATIONAL MONUMENT BETWEEN FRENCH FRIGATE SHOALS AND LAYSAN ISLAND. LARGE SWELLS FROM THE SOUTHEAST CAN BE EXPECTED OVER THE SMALL ISLANDS AND SHOALS WITHIN THE MONUMENT AS EARLY AS THURSDAY. FORECAST POSITIONS AND MAX WINDS INITIAL 21/0300Z 15.5N 165.2W 65 KT 12HR VT 21/1200Z 16.8N 166.3W 75 KT 24HR VT 22/0000Z 18.2N 167.2W 80 KT 36HR VT 22/1200Z 19.3N 167.7W 90 KT 48HR VT 23/0000Z 20.4N 168.3W 95 KT 72HR VT 24/0000Z 22.2N 169.3W 95 KT 96HR VT 25/0000Z 23.6N 170.3W 90 KT 120HR VT 26/0000Z 25.1N 171.0W 80 KT $$ FORECASTER WROE