WDPN32 PGTW 042100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 05W (FIVE) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.1N 117.4E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 222 NM SOUTHEAST OF HONG KONG MOVEMENT PAST 6 HOURS: WESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL STORM (TS) 05W WITH WIDESPREAD BUILDING CONVECTION OVER THE CENTER AND SOUTHERN PERIPHERY OF A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). THE LOW-LEVEL STRUCTURE APPEARS TO BE FURTHER CONSOLIDATING COMPARED TO 6 HOURS AGO, BUT NORTHERLY SHEAR IS PREVENTING THE SYSTEM FROM BECOMING MORE VERTICALLY STACKED. ENVIRONMENTAL ANALYSIS INDICATES THAT 05W IS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG EQUATORWARD OUTFLOW ALOFT, LOW (10-15 KTS) NORTHERLY VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC IN ANIMATED EIR IMAGERY. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE HIGH END OF AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A SUBTROPICAL RIDGE POSITIONED TO THE NORTH AND A NEAR-EQUATORIAL RIDGE BUILDING TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS KNES: T2.5 - 35 KTS CIMSS SATCON: 37 KTS AT 041713Z CIMSS ADT: 37 KTS AT 041800Z CIMSS AIDT: 37 KTS AT 041800Z CIMSS DPRINT: 30 KTS AT 041800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG 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 05W IS FORECAST TO BEGIN TRACKING SLOWLY NORTHWARD THROUGH TAU 24 AS THE SUBTROPICAL RIDGE TO THE SOUTHEAST CONTINUES TO BUILD. ACTUAL TRACK MOTION IS UNCERTAIN THROUGH TAU 24 THOUGH, AS THE STEERING PATTERN REMAINS COMPETING. AFTER TAU 24, THE STEERING PATTERN WILL BE MORE DEFINED AND THE SYSTEM WILL PICK UP SPEED IN THE NORTH-NORTHEASTWARD DIRECTION, ALONG THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. THIS TRAJECTORY WILL CONTINUE THROUGH TAU 72, WHEN RIDGING TO THE NORTH WILL STOP THE VORTEX AND DRIVE IT WESTWARD INTO MAINLAND CHINA. IN TERMS OF INTENSITY, 05W IS FORECAST TO QUICKLY INTENSIFY OVER THE NEXT 24 HOURS AS THE NORTHERLY SHEAR BEGINS TO BACK OFF. A PEAK INTENSITY OF 75 KTS IS FORECAST TO OCCUR AROUND TAU 36-48. NEAR TAU 72, 05W WILL BEGIN INCHING TOWARD THE COAST OF CHINA AND LAND INTERACTION WILL BEGIN TO WEAK THE SYSTEM. ADDITIONALLY, DRY AIR WILL LIKELY ADVECT OFF THE MOUNTAINS AND INTO THE VORTEX. AFTER TAU 72, SIGNIFICANT TERRAIN INTERACTION WILL CAUSE 05W TO RAPIDLY WEAKEN AS THE REMNANT VORTEX MOVES OFF TO THE WEST. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN MODERATE AGREEMENT THROUGH TAU 72 WITH A 143 NM CROSS-TRACK SPREAD AT TAU 72. HOWEVER, MODELS DRASTICALLY DIFFER AFTER TAU 72, WITH MODELS DEPICTING LARGE VARIATIONS IN TRACK POSSIBILITIES. GFS DETERMINISTIC, ECMWF DETERMINISTIC, AND ECMWF ENSEMBLE MEAN ALL TAKE THE VORTEX WESTWARD INTO MAINLAND CHINA WHILE THE JGSM, UKMET, AND GFS ENSEMBLE MEAN HAVE THE VORTEX MAKING A SHARP TURN BACK TO THE SOUTHWEST. THE JTWC TRACK IS PLACED MORE IN LINE WITH THE FIRST SCENARIO WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE IS IN RELATIVELY GOOD AGREEMENT, HOWEVER, WITH THE TRACK BEING SO CLOSE TO LAND ON EITHER SIDE, A SMALL VARIATION IN THE TRACK COULD CAUSE LARGE CHANGES TO THE INTENSITY OF THE STORM. MODELS GENERALLY HAVE THE SYSTEM INTENSIFYING THROUGH TAU 48 AND THEN WEAKENING THEREAFTER THOUGH. MULTIPLE RAPID INTENSIFICATION AIDS CONTINUE TO TRIGGER, SO THE INITIAL INTENSIFICATION TREND MAY BE A BIT HIGHER THAN FORECASTED. OVERALL, THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH LOW CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN