WDPN32 PGTW 011500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (CHABA) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.6N 112.9E INITIAL INTENSITY: 60 KTS GEOGRAPHIC REFERENCE: 178 NM SOUTH-SOUTHWEST OF HONG KONG MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 24 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SPIRAL BANDS OF DEEP CONVECTION WRAPPING INTO A DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). A 011035Z SSMIS 91GHZ IMAGE DEPICTED FORMATIVE BANDING WRAPPING INTO THE LLCC WITH A BROAD AND FRAGMENTED MICROWAVE EYE FEATURE, WHILE THE 37GHZ IMAGE SHOWED THAT SMALL EYE FEATURE SEEN IN EARLIER IMAGERY HAS BECOME MORE RAGGED AND LESS DEFINED WITHIN THE LAST 6 HOURS. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE MORE RAGGED 37GHZ EYE FEATURE, ALONG WITH MULTI- AGENCY POSITION FIXES. THE FIRST HINTS THE CENTER WERE ALSO EVIDENT IN ANIMATED RADAR IMAGERY, DISPLACED TO THE WEST OF THE INITIAL POSITION AS THE RADAR IS SEEING THE UPPER LEVEL ROTATION. THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE CONVECTIVE STRUCTURE AS WELL AS A COMBINATION OF AGENCY DVORAK INTENSITY ESTIMATES AND OBJECTIVE ADT AND SATCON ESTIMATES. ENVIRONMENTAL CONDITIONS ARE FAVORABLE WITH WARM SSTS (29-30C), LOW (10-15 KTS) EASTERLY VWS AND MODERATE TO STRONG EQUATORWARD OUTFLOW INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A MID TO UPPER-LEVEL SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T4.0 - 65 KTS KNES: T4.0 - 65 KTS CIMSS SATCON: 58 KTS AT 011226Z CIMSS ADT: 55 KTS AT 011140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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 04W (CHABA) IS FORECAST TO CONTINUE TRACKING NORTHWESTWARD, BEING PUSHED TOWARD THE CHINESE COAST BY THE MID-LEVEL STEERING RIDGE CURRENTLY OVER THE NORTHERN PHILIPPINES. THE SYSTEM IS EXPECTED TO MAKE LANDFALL NEAR THE LUICHOW PENINSULA NEAR TAU 24. TRACK SPEED HAS SLOWED SLIGHTLY AS A MID-LEVEL RIDGE HAS BUILT IN TO THE NORTH OF THE SYSTEM OVER SOUTHERN CHINA. THIS RIDGE IS FORECAST TO WEAKEN OVER THE NEXT 24 HOURS. AS THE RIDGE WEAKENS AND ERODES FROM THE WEST, TS 04W WILL TURN INTO THE RESULTING WEAKNESS IN THE RIDGE AND TURN MORE POLEWARD AFTER MAKING LANDFALL. IN THE NEAR-TERM, THE SYSTEM LOOKS TO POTENTIALLY CASH IN ON SOME DIVERGENT FLOW ALOFT, WEAKENING THE ALREADY LOW SHEAR, WHICH WILL ALLOW FOR CONVECTIVE CONSOLIDATION AND INTENSIFICATION TO A PEAK OF 70 KNOTS PRIOR TO LANDFALL. SOME RAPID INTENSIFICATION GUIDANCE IS STILL TRIGGERING WITH THIS RUN, AND THUS IT IS STILL POSSIBLE TO SEE A SLIGHTLY HIGHER PEAK OCCUR JUST PRIOR TO LANDFALL AS THE SYSTEM MOVES OVER SHALLOW, WARM COASTAL WATERS. ONCE ASHORE, THE WILL RAPIDLY WEAKEN DUE TO TERRAIN INTERACTION, ULTIMATELY DISSIPATING OVER SOUTHERN CHINA BY TAU 48. MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT, WITH THE MINIMAL SPREAD THROUGH THE FORECAST PERIOD. THE JTWC REMAINS CONSISTENT WITH THE PREVIOUS FORECAST AND LIES NEAR THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN RELATIVELY GOOD AGREEMENT, WITH A 20 KNOT SPREAD BETWEEN THE RIPA PEAK OF 75 KNOTS AND THE HWRF, WHICH CONTINUES TO SHOW GENERALIZED WEAKENING TREND WITH A MAXIMUM OF 55 KNOTS BY TAU 12. THE JTWC FORECAST CLOSELY TRACKS THE RIPA AND COAMPS-TC GUIDANCE THROUGH LANDFALL THEN LIES CLOSE TO THE CONSENSUS MEAN THEREAFTER WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN