WDPN31 PGTW 040300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (YAGI) WARNING NR 011// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.1N 117.7E INITIAL INTENSITY: 70 KTS GEOGRAPHIC REFERENCE: 275 NM SOUTHEAST OF HONG KONG MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 27 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TYPHOON (TY) 12W (YAGI) HAS NOW RAPID INTENSIFIED, FROM 40 KNOTS 24 HOURS AGO, TO 70 KNOTS AT 040000Z, WITH ADDITIONAL RI EXPECTED IN THE COMING DAYS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS DEEP CONVECTION FIRING OFF ON THE EASTERN SIDE OF THE LOW LEVEL CIRCULATION CENTER (LLCC), AND POCKETS OF FLARING CONVECTIVE ACTIVITY STEADILY ORGANIZING INTO FEEDER BANDS TO THE WEST AND SOUTHWEST. THE SYSTEM FLIRTED WITH DEVELOPING AN EYE AROUND 2200Z, WHICH FAILED TO PERSIST. AS REVEALED BY A 032238Z SSMIS 37GHZ MICROWAVE IMAGE HOWEVER, THE LOW-LEVEL STRUCTURE IS ROBUST, WITH A WELL-DEFINED MICROWAVE EYE FEATURE. THE COLOR ENHANCED 37GHZ IMAGE ALSO SHOWS A CYAN RING FEATURE, INDICATIVE OF A HIGH PROBABILITY OF ADDITIONAL RI. THE MICROWAVE IMAGE ALSO REVEALS A WEAKER CONVECTIVE STRUCTURE ON THE NORTHWEST SIDE, WHICH HINTS AT THE CONTINUED PRESENCE OF A PLUG OF DRY AIR IN THAT QUADRANT. THIS IS BACKED UP BY THE LACK OF PERSISTENT CONVECTIVE ACTIVITY IN THE MSI IN THAT QUADRANT. THE INITIAL POSITION WAS ASSESSED WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION OF THE MICROWAVE EYE FEATURE DISCUSSED ABOVE. THE INITIAL INTENSITY WAS ASSESSED WITH MEDIUM CONFIDENCE BASED ON BLEND OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED BELOW. WITH THE EXCEPTION OF THE LINGERING DRY AIR TO THE NORTHWEST, THE SYSTEM LIES IN A HIGHLY FAVORABLE ENVIRONMENT, WITH LOW VWS, WARM SSTS, HIGH OHC AND STRONG EQUATORWARD OUTFLOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER STR OVER CHINA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS RJTD: T4.5 - 77 KTS RCTP: T4.0 - 65 KTS KNES: T5.0 - 90 KTS CIMSS ADT: 74 KTS AT 030000Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 5-10 KTS SST: 31-32 CELSIUS OUTFLOW: STRONG EQUATORWARD OTHER FACTORS: DRY MID-LEVEL AIR TO THE NORTHWEST. 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: TY 12W IS FORECAST TO TRACK WESTWARD ALONG THE SOUTHERN SIDE OF THE STEERING RIDGE OVER CHINA FOR THE FIRST 36 HOURS OF THE FORECAST. A SLIGHT JOG TO A MORE WEST-NORTHWEST TRACK IS FORECAST AFTER TAU 36 AS THE RIDGE SLIDES TO THE EAST AND THE STEERING GRADIENT ORIENTATION SHIFTS TO A MORE WEST-NORTHWEST TO EAST-SOUTHEAST AXIS. THE LATEST FORECAST CALLS FOR THE SYSTEM TO SKIRT THE NORTHEASTERN TIP OF HAINAN ISLAND, PASS THROUGH THE HAINAN STRAIT AND EMERGE INTO THE GULF OF TONKIN, ALL DURING THE 24 HOUR PERIOD BETWEEN TAU 48 AND TAU 72. LANDFALL NEAR HAIPHONG, VIETNAM IS EXPECTED SHORTLY AFTER TAU 72, WITH THE SYSTEM QUICKLY MOVING INLAND THEREAFTER. IN TERMS OF INTENSITY, THE SYSTEM HAS ALREADY RAPIDLY INTENSIFIED OVER THE PREVIOUS 24 HOURS, AND FURTHER RI IS ANTICIPATED. THE LATEST MSI SUGGESTS A BIT OF DRY AIR LINGERS TO THE NORTHWEST, LIMITING THE INTENSIFICATION TREND SOMEWHAT BY NOT ALLOWING FOR THE EYEWALL TO COMPLETELY CLOSE OFF. ALL AVAILABLE GUIDANCE INDICATES THIS DRY AIR WILL VACATE THE PREMISES IN THE SHORT-TERM, AND ALLOW FOR CONVECTIVE CONSOLIDATION AND VORTEX SYMMETRIZATION. AS SOON AS THIS PROCESS COMPLETES, EXPECTED IN THE NEXT 6-12 HOURS AT MOST, THE SYSTEM WILL EMBARK ON ANOTHER ROUND OF RI. THE CURRENT FORECAST POINTS CALL FOR A PEAK OF 115 KNOTS AT TAU 36 AND TAU 48. IN REALITY, A HIGHER PEAK IS POSSIBLE BETWEEN THESE TWO POINTS, AS INDICATED BY SOME OF THE RI GUIDANCE. THE SYSTEM WILL WEAKEN SIGNIFICANTLY AS IT PASSES THROUGH THE HAINAN STRAIT DUE TO TERRAIN INTERACTION AND AN INCREASE IN VWS. ONCE OVER THE GULF OF TONKIN, THE SYSTEM IS LIKELY TO AT LEAST MAINTAIN INTENSITY THROUGH LANDFALL AS A SIGNIFICANT TYPHOON. ONCE OVER LAND, THE SYSTEM WILL RAPIDLY WEAKEN AND DISSIPATE NO LATER THAN TAU 120 MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE REMAINS IN GOOD AGREEMENT, WITH A CROSS-TRACK SPREAD OF ABOUT 115NM AT TAU 72, BOUNDED BY THE NAVGEM ON THE NORTH AND ECMWF ON THE SOUTH. CROSS-TRACK SPREAD REMAINS CONSISTENT THROUGH THE END OF THE FORECAST, BUT ALONG-TRACK SPREAD INCREASES SHARPLY AFTER TAU 72, ESPECIALLY AFTER THE SYSTEM MOVES INLAND AND DISSIPATES. THE JTWC TRACK IS HEDGED SLIGHTLY NORTH OF THE CONSENSUS MEAN, TOWARDS THE GFS, THROUGH THE DURATION OF THE FORECAST. INTENSITY GUIDANCE IS ALSO IN FAIRLY GOOD AGREEMENT, THOUGH THE HAFS-A AND HWRF NOW PEAK OUT AT AROUND 105 KNOTS. ANALYSIS SUGGESTS THIS IS DUE TO PREDICTION OF AN EYEWALL REPLACEMENT CYCLE (EWRC) STARTING AROUND TAU 36, WHICH IS LEADING TO A DECREASE IN INTENSITY IN THESE MODELS. WHILE IT IS CERTAINLY POSSIBLE THIS COULD OCCUR, AT THIS POINT ITS TOO EARLY TO MAKE THAT CALL. NEARLY ALL RI AIDS CONTINUE TO TRIGGER, WITH THE RI55 AND FRIA AIDS PEAKING THE SYSTEM AT 125 KNOTS. THE JTWC FORECAST LIES AMONGST THE RI AIDS, AND IS ABOVE THE CONSENSUS BY ABOUT 10 KNOTS, BUT STAYS BELOW THE MOST AGGRESSIVE RI AIDS AT THE PEAK. A PEAK OF 120 KNOTS IS POSSIBLE HOWEVER, BETWEEN TAU 36 AND 48, AS DISCUSSED ABOVE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN