WDPN31 PGTW 071500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (CONSON) WARNING NR 007// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.0N 122.8E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 142 NM SOUTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAGGED APPEARANCE, WITH FLARING CONVECTION WEAKLY WRAPPING INTO A BROAD LOW LEVEL CIRCULATION CENTER (LLCC). FOR A BRIEF PERIOD OF TIME AFTER MOVING OVER THE CONFINED WATERS OF THE SIBUYAN SEA, NEAR THE 1100Z HOUR, THE SYSTEM DEVELOPED A WELL-DEFINED RADAR EYE FEATURE. SUBSEQUENT RADAR DATA INDICATES THE EYE HAS ALREADY STARTED TO BECOME MORE RAGGED AND IS LOSING SOME OF ITS STRUCTURE. THE RADAR DATA DID HOWEVER PROVIDE HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY OF 55 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON THE AVERAGE OF MULTI-AGENCY DVORAK ESTIMATES AS WELL OBJECTIVE ADT ESTIMATES, AND TAKING INTO ACCOUNT THE APPEARANCE OF THE RADAR EYE. WHILE THE RADAR IMAGERY PROVIDED COMPELLING EVIDENCE OF A POTENTIALLY HIGHER INITIAL INTENSITY, THE SATELLITE IMAGERY WAS NOT AS IMPRESSIVE WITH THE LACK OF ANY ORGANIZED CONVECTIVE STRUCTURE AND RELATIVELY WARM CLOUD TOPS. A PARTIAL 071107Z ASCAT-A PASS SHOWED ONE 50 KNOT WIND VECTOR ON THE VERY EDGE OF THE SWATH WITH SEVERAL 40-45 KNOT VECTORS TO THE SOUTHEAST, WHICH LEND ADDITIONAL CONFIDENCE TO THE INITIAL INTENSITY. OVERALL TS 18W LIES IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY WARM SSTS, LOW VWS AND MODERATE RADIAL OUTFLOW WITH WEAK POLEWARD OUTFLOW INTO A WEAK TUTT CELL TO THE NORTH. INITIAL WIND RADII BASIS: PERSISTENCE AND PARTIAL ASCAT DATA. CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF NEAR EQUATORIAL RIDGE (NER) TO THE EAST, TRANSITIONING TO DEEP SUBTROPICAL RIDGE (STR) TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.0 - 65 KTS RJTD: T2.5 - 35 KTS KNES: T3.5 - 55 KTS CIMSS ADT: 53 KTS AT 071140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 0-5 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 18W IS FORECAST TO TRACK NORTHWESTWARD THROUGH TAU 48 ALONG THE WESTERN SIDE OF THE NER TO THE EAST, BEFORE THE STR TO THE NORTH-NORTHEAST TAKES OVER STEERING ABOUT TAU 24. AFTER MOVING THROUGH THE MANILA METRO AREA, THE SYSTEM IS EXPECTED TO MOVE BACK OVER WATER NEAR TAU 36, THEN SHIFT TO A MORE WEST-NORTHWEST TRACK THROUGH THE REMAINDER OF THE FORECAST. THE TRACK HAS SLOWED SOMEWHAT AS IT APPROACHES HAINAN ISLAND, AS THE STEERING PATTERN WEAKENS AND BECOMES LESS CERTAIN. AS WAS MENTIONED AS A POSSIBILITY IN THE PREVIOUS FORECAST, TS 18W HAS IN FACT UNDERGONE A BRIEF PERIOD OF INTENSIFICATION AS IT MOVED OVER THE WARM, SHALLOW WATERS OF THE SIBUYAN SEA. HOWEVER, THIS TREND IS NOT EXPECTED TO LAST, AS THE SYSTEM MOVES NORTHWESTWARD AND WILL BEGIN TO BE DISRUPTED BY TERRAIN INTERACTION AS IT MOVES ALONG THE COAST OF SOUTHEASTERN LUZON OVER THE NEXT 12 HOURS. AFTER LANDFALL, STEADY WEAKENING IS EXPECTED AS THE SYSTEM WILL STRUGGLE TO MAINTAIN A SOLID LOW LEVEL CORE OVER THE RUGGED TERRAIN. ONCE OVER WATER AGAIN, THE SYSTEM SHOULD SLOWLY INTENSIFY TO A PEAK OF 65 KNOTS UNDER MODERATELY FAVORABLE CONDITIONS OF LOW TO MODERATE VWS, AND WARM SSTS OFFSET SOMEWHAT BY WEAK EASTERLY FLOW ALOFT LIMITING OUTFLOW. MODEL DISCUSSION: NUMERICAL TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH TAU 48, WITH MINIMAL CROSS-TRACK SPREAD. AFTER TAU 48 HOWEVER, THERE IS NOW SIGNIFICANT UNCERTAINTY IN THE MODEL GUIDANCE. THERE ARE NOW THREE DISTINCT SCENARIOS IN THE GUIDANCE. THE FIRST IS REPRESENTED BY THE COAMPS FAMILY OF MODELS AS WELL AS THE ECMWF ENSEMBLE, TAKING THE SYSTEM MORE POLEWARD AFTER ENTERING THE SCS, THEN TURNING NORTHWARD BY TAU 96 TO THE EAST OF HAINAN. THE SECOND SOLUTION REPRESENTED BY THE ECMWRF DETERMINISTIC AND UKMET IS A TRACK CONSISTENT WITH PREVIOUS FORECASTS, JUST SOUTH OF HAINAN. THE THIRD SOLUTION REPRESENTED BY GFS AND ITS ENSEMBLE IS TO TRACK THE SYSTEM INTO THE CENTRAL SCS BEFORE TURNING SHARPLY BACK TO THE EAST WHILE DISSIPATING. THE NAVGEM SOLUTION IS DISCOUNTED AS IT SHOWS A 120 DEGREE TURN NORTHEAST IMMEDIATELY AFTER EMERGENCE OVER WATER. THE JTWC TRACK REMAINS CONSISTENT WITH THE PREVIOUS FORECAST THOUGH MUCH SLOWER THE EXTENDED FORECAST, WITH LOW CONFIDENCE BEYOND TAU 72. THE INTENSITY GUIDANCE IS ALSO MIXED, WITH HWRF CONTINUING TO SHOW MASSIVE INTENSIFICATION IN THE SCS, WHILE GFS FULLY DISSIPATES THE SYSTEM AFTER ITS REMNANTS ENTER THE SCS AT TAU 48. THE JTWC FORECAST LIES CLOSE THE CONSENSUS MEAN WITH LOW CONFIDENCE DUE TO THE UNCERTAINTIES IN THE INTENSITIES OVER LAND. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN