WDPN31 PGTW 230300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01C (PEWA) WARNING NR 27// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 01C (PEWA), LOCATED APPROXIMATELY 454 NM NORTH- NORTHEASTWARD OF WAKE ISLAND, HAS TRACKED NORTH-NORTHWESTWARD AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS WEAKENING DEEP CONVECTION OVER A WELL DEFINED, ALBEIT PARTIALLY EXPOSED, LOW-LEVEL CIRCULATION CENTER (LLCC). A 222203Z METOP-A MICROWAVE IMAGE REVEALS THE LLCC WITH THE BULK OF THE DEEP CONVECTION SHEARED TO THE EAST AND DRIER AIR APPROACHING FROM THE NORTHEAST. THE INITIAL POSITION IS BASED ON THE MSI AND THE AFOREMENTIONED IMAGERY WITH FAIR CONFIDENCE. THE INITIAL INTENSITY OF 35 KNOTS IS BASED ON CONGRUENT DVORAK CURRENT ESTIMATES FROM PGTW AND RJTD. UPPER-LEVEL ANALYSIS INDICATES PERSISTENT VERTICAL WIND SHEAR (VWS) ASSOCIATED WITH A TROPICAL UPPER-TROPOSPHERIC TROUGH (TUTT) CELL TO THE NORTHWEST OF THE SYSTEM CONTINUES TO HAMPER TS 01C AND LIMIT DEVELOPMENT DESPITE GOOD RADIAL OUTFLOW. TS 01C IS TRACKING NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED EAST OF THE SYSTEM. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 01C WILL CONTINUE TO TRACK NORTHWESTWARD THROUGH TAU 24 UNDER THE INFLUENCE OF THE CURRENT STEERING STR AND NEIGHBORING TUTT CELL. TS PEWA IS EXPECTED TO SLOWLY INTENSIFY THROUGH THIS PERIOD AS THE TUTT CELL THAT IS CURRENTLY HAMPERING THE SYSTEM BEGINS TO INCREASE SEPARATION DISTANCE. THIS WILL ALLOW THE VWS TO RELAX AND POLEWARD OUTFLOW TO IMPROVE. BETWEEN TAU 24 AND TAU 48, TS O1C IS FORECAST TO MOVE INTO A WEAK STEERING ENVIRONMENT AS AN APPROACHING MID-LATITUDE TROUGH BREAKS THE STEERING RIDGE AND SLOWS THE SYSTEM; ALLOWING TS 01C TO REACH A PEAK INTENSITY OF 45 KTS. AFTER TAU 48, TS 01C IS FORECAST TO RECURVE AS THE SYSTEM BEGINS TO TURN POLEWARD AND EVENTUALLY NORTHEASTWARD AND TRACK OUT AHEAD OF THE TROUGH UNDER THE INFLUENCE OF INCREASING MID-LATITUDE WESTERLY FLOW. TS 01C IS FORECAST TO BEGIN EXTRATROPICAL TRANSITION BY TAU 72 AS INCREASING VWS OUT AHEAD OF THE TROUGH ALONG WITH COOLER SEA SURFACE TEMPERATURES BEGIN TO WEAKEN THE SYSTEM. THE POSSIBILITY OF DISSIPATION BELOW WARNING THRESHOLD BEFORE THIS SYSTEM BEGINS EXTRATROPICAL TRANSITION REMAINS DUE TO HIGH VWS AND DRY AIR BEGINNING TO SURROUND THE STORM. DESPITE THE POSSIBILITY FOR EARLY DISSIPATION, CONFIDENCE IN THE TRACK FOR THIS PORTION OF THE FORECAST IS HIGH. C. IN THE EXTENDED PERIOD, TS 01C IS EXPECTED TO COMPLETE EXTRATROPICAL TRANSITION BY TAU 96. THE NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH A SLIGHT SPREAD IN POSITION AND TRACK SPEEDS AT LATER TAUS DUE TO VARYING INTERPRETATIONS OF THE EXTRATROPICAL TRANSITION. THE JTWC FORECAST IS IN AGREEMENT WITH THE MULTI-MODEL CONSENSUS, WHICH INDICATES RAPID ACCELERATION PAST TAU 48 INTO THE WESTERLIES WITH EXTRATROPICAL TRANSITION BY TAU 96. THERE IS LOW CONFIDENCE IN THE TRACK FOR THE EXTENDED PORTION OF THE FORECAST DUE TO VARYING SOLUTIONS IN THE POSITION AND TRACK SPEED OF THE SYSTEM.// NNNN