WDPN32 PGTW 231500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (NORU) WARNING NR 007// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.0N 131.8E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 556 NM SOUTH-SOUTHEAST OF KADENA AB MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 16 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS PERSISTENT CONVECTION WRAPPING AROUND A LOW-LEVEL CIRCULATION (LLCC). A SLIGHT TILT STILL EXISTS WITH THE LLCC WITH EASTERLY SHEAR SLIGHTLY INCREASING OVER THE LAST 6 HOURS. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE USING THE EIR LOOP AND MULTIPLE AGENCY DVORAK FIX POSITIONS. THE INITIAL INTENSITY IS PLACED WITH MEDIUM CONFIDENCE BASED ON A COMBINATION OF SUBJECTIVE AND OBJECTIVE AGENCY DVORAK INTENSITY ESTIMATES LISTED BELOW. UPPER-LEVEL CONDITIONS REMAIN FAVORABLE WITH FAIR WESTWARD AND FAIR EQUATORWARD OUTFLOW AND LOW TO MODERATE EASTERLY VERTICAL WIND SHEAR. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T2.5 - 35 KTS KNES: T3.0 - 45 KTS CIMSS ADT: 35 KTS AT 231220Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: WEAK WESTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS NORU IS CONTINUING ON A WESTWARD TRACK TOWARDS LUZON. DURING THE NEXT 12 TO 24 HOURS, THE SYSTEM WILL CONTINUE TRACKING WESTWARD UNDER THE INFLUENCE OF A DEEP-LAYER SUBTROPICAL RIDGE TO THE NORTHEAST. THIS DOMINANT STEERING FEATURE WILL STEER TS NORU TOWARD THE COAST OF LUZON, JUST BEFORE IT MAKES ITS INITIAL LANDFALL BETWEEN TAUS 36 AND 48. THE STRONGER EASTERLY CONVERGENT FLOW ALOFT, AND WEAK UPPER-LEVEL OUTFLOW, ALONG WITH THE MID-LEVEL DRY AIR, ARE FORECASTED TO ALLOW THE SYSTEM TO MAINTAIN A GRADUAL INTENSIFICATION UP TO 60 KNOTS BEFORE LANDFALL. ONCE OVERLAND, THE SYSTEM WILL INTERACT WITH THE TERRAIN, SLOWING ANY FURTHER INTENSIFICATION. HOWEVER, A DIFFERENT STORY OCCURS FOR TS NORU ONCE IT MOVES BACK OVER THE SOUTH CHINA SEA. RAPID INTENSIFICATION REMAINS A POSSIBILITY ONCE THE SYSTEM MOVES BACK OVER WATER, TS NORU WILL ENJOY A MORE FAVORABLE ENVIRONMENT WITH VERY WARM WATERS, LOW VERTICAL WIND SHEAR, AND AN ENHANCED UPPER-LEVEL ENVIRONMENT. THE FAVORABLE ENVIRONMENT WILL HELP INTENSIFY THIS SYSTEM JUST SOUTHEAST OF HAINAN, CHINA. THE POTENTIAL FOR THE RAPID INTENSIFICATION IS MOST PREVALENT NEAR TAU 72 AND BEFORE 96 IN THE MODEL CONSENSUS. HOWEVER, THE OFFICIAL JTWC INTENSITY PEAK AT THIS TIME WILL REMAIN AT 80 KNOTS. SHORTLY AFTER TAU 96, TS NORU WILL MAKE ITS SECONDARY LANDFALL OVER VIETNAM, JUST NORTH OF HUE CITY. MODEL DISCUSSION: NUMERICAL MODELS REMAIN IN OVERALL TIGHT AGREEMENT WITH NVGM THE NORTHERNMOST OUTLIER AND GFS THE SOUTHERNMOST OUTLIER. MODEL TRACK GUIDANCE REMAINS TIGHT THROUGH THE NEXT 72 HOURS, WITH ONLY A SPREAD OF 110NM, MAXING OUT TO 200NM FROM TAU 96 AND BEYOND, LENDING HIGH CONFIDENCE IN THE OVERALL JTWC TRACK FOR THE FIRST 72 HOURS AND MEDIUM THEREAFTER. THE BULK OF THE INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH ALL BUT THE COAMPS-TC, WHICH PEAKS THE INTENSITY AT 105 KNOTS, THE OPPOSITE HAPPENS FOR THE GFS TREND SHOWING ONLY A PEAK OF 55 KNOTS. THE JTWC FORECAST LIES SLIGHTLY ABOVE THE MEAN THROUGHOUT THE FORECAST PERIOD, LENDING ONLY MEDIUM CONFIDENCE IN THE JTWC INTENSITY FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN