WTPA42 PHFO 190900 TCDCP2 TROPICAL DEPRESSION THREE-C DISCUSSION NUMBER 3 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP032009 1100 PM HST SUN OCT 18 2009 TROPICAL DEPRESSION THREE-C IS LIKELY A RARE SYSTEM IN THE CENTRAL PACIFIC...WHICH SEEMS OUT OF PLACE FROM THE TYPICAL DEVELOPING TROPICAL CYCLONES WE SEE HERE. IT ORIGINATED ALONG A VERY WELL DEFINED MONSOON TROUGH THAT HAD BEEN ESTABLISHED FAR SOUTH OF THE ALOHA STATE FOR SEVERAL DAYS NOW. JUST 24 HOURS AGO...THE PRECURSOR CLOUD SYSTEM FOR THREE-C WAS AN EAST NORTHEAST TO WEST SOUTHWEST ORIENTED MONSOON GYRE. THIS LARGE GYRE BECAME MORE CONCENTRATED OVERNIGHT...AND BY 18/1500 UTC THIS MORNING IT HAD DEVELOPED A MUCH MORE CIRCULAR APPEARANCE. OUR COLLEAGUES WHO DEAL WITH MANY DEVELOPING TROPICAL CYCLONES OVER THE NORTHWEST PACIFIC OCEAN TYPICALLY SEE THESE TYPES OF SYSTEMS ONE OR MORE TIMES PER YEAR. THIS IS IMPORTANT FOR OUR UNDERSTANDING OF THE SLOW...BUT STEADY... DEVELOPMENT OF THREE-C. THESE LARGE MONSOON SYSTEMS TEND TO DEVELOP RATHER SLOWLY. HOWEVER...ONE SHOULD NOT UNDERESTIMATE THEIR POTENTIAL TO ULTIMATELY BECOME AN INTENSE TROPICAL CYCLONE. EVEN THOUGH THE CLOUD TOPS ASSOCIATED WITH THREE-C HAD WARMED CONSIDERABLY DURING THE DAYTIME DIURNAL MINIMUM...THE COLDEST THUNDERSTORM TOPS ARE NOW CLOSE TO MINUS 76C. THESE THUNDERSTORMS ALSO APPEAR TO BE REDEVELOPING CLOSE TO THE APPARENT CENTER OF THE TROPICAL DEPRESSION. AS MENTIONED ABOVE...THE SIGNATURE OF THREE-C IN SATELLITE IMAGERY IS VERY IMPRESSIVE DUE TO ITS LARGE SIZE. THIS IS ALSO TRUE IN WATER VAPOR IMAGERY...WHICH INDICATES A LARGE AREA OF UPPER LEVEL MOISTURE SURROUNDING THE SYSTEM. OUTFLOW ABOVE THE LOW-LEVEL FEATURE IS ALSO RATHER IMPRESSIVE...WITH A LARGE ANTICYCLONIC CIRCULATION EVIDENT OVER THREE-C. THE LATEST UW/CIMSS VERTICAL WIND SHEAR ANALYSIS FOR THREE-C INDICATES 2 KT FROM 60 DEGREES. THE SATELLITE FIX AGENCIES...PHFO...JTWC AND SAB...WERE IN RELATIVELY CLOSE AGREEMENT IN THE LOCATION OF THE LOW-LEVEL CIRCULATION CENTER. THESE AGENCIES ALSO INDICATED T NUMBERS OF 1.5 TO 2.0. THE QUIKSCAT PASS APPEARED TO SHOW ONE 35 KT WIND BARB ABOUT 55 NM NORTHEAST OF THE APPARENT CENTER. DUE TO THE LACK OF DEEP CONVECTION AT 0600 UTC...HAVE MAINTAINED THREE-C AS A 30 KT TROPICAL DEPRESSION FOR THIS PACKAGE. THE LACK OF DEEP CONVECTION MAY BE ONE REASON THREE-C IS CONTINUING TO MOVE AT 275/17. THE CONSENSUS AND INDIVIDUAL TRACK FORECAST MODELS CONTINUE TO INDICATE THAT THREE-C WILL GRADUALLY TURN TOWARD THE WEST NORTHWEST...AND THEN NORTHWEST AT A SLIGHTLY SLOWER FORWARD MOTION OVER THE NEXT 36 TO 48 HOURS. THIS IS IN RESPONSE TO RIDGING TO THE NORTHEAST OF THE SYSTEM...AS WELL AN UPPER LEVEL TROUGH TO THE NORTHWEST. THE LATEST TRACK FORECAST WAS NUDGED SLIGHTLY TO THE LEFT OF THE PREVIOUS ONE THROUGH 24-36 HOURS...BUT THEN WAS BLENDED BACK TO THE PREVIOUS TRACK FORECAST THEREAFTER. MARGINAL OCEAN HEAT CONTENT VALUES ACCORDING TO THE CIRA ANALYSIS... ALONG WITH SEA SURFACE TEMPERATURES OF 28-29 C ALONG THREE-C/S FORECAST TRACK...APPEAR FAVORABLE FOR INTENSIFICATION. IN ADDITION...THE UW/CIMSS FORECAST INDICATES LOW VALUES OF VERTICAL WIND SHEAR ALONG THE SYSTEM/S TRACK. THEREFORE...NUDGED THE LATEST INTENSITY FORECAST TOWARD THE ICON...WHICH BRINGS THE SYSTEM TO MINIMAL HURRICANE INTENSITY TWO DAYS FROM NOW. THREE-C REMAINS FAR SOUTH OF THE HAWAIIAN ISLANDS. HOWEVER...BASED ON THE CURRENT FORECAST...ANYONE IN THE VICINITY OF JOHNSTON ISLAND NEEDS TO CLOSELY MONITOR FUTURE ADVISORIES. THE CURRENT FORECAST TAKES THREE-C NEAR THAT ISLAND WITHIN THE NEXT 72 HOURS AS A HURRICANE. FORECAST POSITIONS AND MAX WINDS INITIAL 19/0900Z 8.9N 158.9W 30 KT 12HR VT 19/1800Z 9.6N 161.1W 40 KT 24HR VT 20/0600Z 11.3N 163.6W 45 KT 36HR VT 20/1800Z 12.9N 165.4W 55 KT 48HR VT 21/0600Z 14.5N 167.0W 65 KT 72HR VT 22/0600Z 16.4N 169.2W 70 KT 96HR VT 23/0600Z 18.0N 171.6W 80 KT 120HR VT 24/0600Z 19.2N 174.0W 85 KT $$ FORECASTER HOUSTON