WDPN31 PGTW 180900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 30W (FENGSHEN) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.0N 124.7E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 236 NM EAST-SOUTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A HIGHLY COMPLEX SITUATION, WITH AN EXTREMELY TILTED AND DISORGANIZED VORTEX AND POTENTIALLY MULTIPLE VORTICES. EARLIER ASCAT DATA AT 180105Z INDICATED A CLEAR-CUT LOW LEVEL CIRCULATION CENTER LOCATED JUST OFF THE COAST OF NORTHEAST SAMAR, WHILE ANIMATED MSI AT THAT TIME SHOWED SIGNIFICANT DEEP CONVECTION FURTHER TO THE SOUTHEAST AND SOME POSSIBLE TURNING IN THE CLEAR AIR TO THE NORTH. A MORE RECENT 180407Z OSCAT-3 PASS SHOWS A WEAK LLCC JUST NORTH OF BANTAYAN BAY ON THE NORTH COAST OF SAMAR 20-30 KNOT WINDS WRAPPING INTO THE CIRCULATION AND HIGHER WINDS TO THE EAST OF SAMAR. A 180408Z GMI 89GHZ MICROWAVE IMAGE MEANWHILE SHOWS A CLEAR-CUT MID-LEVEL CIRCULATION WELL EAST OF SAMAR AND ONLY A VERY WEAK REPRESENTATION OF A LLCC NORTH OF SAMAR. THE MSI LOOP CLEARLY SHOWS SOUTHEASTERLY WINDS TO THE NORTHEAST OF SAMAR, AND FLEETING HINTS OF A POSSIBLE CIRCULATION BETWEEN NORTHERN SAMAR AND CATANDUANES AND SOUTHEASTERN LUZON. SURFACE OBSERVATIONS FROM CATARMAN AND VIRAC HAVE ASSISTED IN NARROWING DOWN THE INITIAL POSITION, WHICH IS PLACED WITH LOW CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, RELIANT UPON THE SCATTEROMETER DATA INDICATING WINDS ASSOCIATED WITH THE LLCC REMAIN LESS THAN 35 KNOTS, AND IN ALIGNMENT WITH THE BULK OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED BELOW. ENVIRONMENTAL CONDITIONS ARE FAVORABLE, WITH VERY WARM SSTS, VERY HIGH OHC, LOW VWS AND GOOD RADIAL OUTFLOW. PROXIMITY TO LAND AND THE HIGHLY TILTED NATURE OF THE VORTEX HOWEVER, ARE CURRENTLY PLACING A SIGNIFICANT HINDRANCE ON DEVELOPMENT. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP LAYER SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T3.0 - 45 KTS RCTP: T2.0 - 30 KTS KNES: T3.0 - 45 KTS CIMSS ADT: 33 KTS AT 180530Z CIMSS AIDT: 32 KTS AT 180530Z CIMSS D-MINT: 29 KTS AT 180453Z CIMSS D-PRINT: 32 KTS AT 180640Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE RADIAL OTHER FACTORS: LARGE AMOUNT OF VORTEX TILT AND DISORGANIZATION. ANALYSIS CONFIDENCE: INITIAL POSITION: LOW INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: IN THE NEAR-TERM (OVER THE NEXT 12 HOURS), THE TRACK OF TD 30W IS LIKELY TO BE HIGHLY ERRATIC, DUE TO THE FACT THAT THERE MAY BE MULTIPLE VORTICES, THE INFLUENCE OF THE LOCALIZED TERRAIN ON THE LLCC MOTION, AND THAT THE VORTEX EXHIBITS SIGNIFICANT TILT AND MISALIGNMENT. OVERALL, OVER THE NEXT 12 HOURS THE SYSTEM IS EXPECTED TO TRACK NORTHWESTWARD, ROUGHLY PARALLEL THE EASTERN COAST OF SOUTHERN LUZON. TRACK SPEEDS ARE FORECAST TO INCREASE OVER THE NEXT 12 HOURS AS THE STEERING GRADIENT TIGHTENS. TD 30W IS EXPECTED TO PASS NEAR POLILLO ISLAND AND THEN MAKE LANDFALL ALONG THE EASTERN COAST OF LUZON AROUND TAU 18, THEN RAPIDLY CROSS LUZON AND REFORM OFF THE WESTERN COAST OF LUZON SHORTLY AFTER TAU 24. THE SYSTEM WILL CONTINUE TRACKING NORTHWESTWARD UNTIL ABOUT TAU 48, WHEN THE OUTER EDGES OF THE CIRCULATION WILL BEGIN TO INTERACT AND RUN INTO THE STRONG NORTHEASTERLY COLD-SURGE FUNNELING SOUTHWARD OUT OF THE TAIWAN STRAIT. BETWEEN TAU 48 AND TAU 72, TRACK SPEEDS SLOW TO FIVE KNOTS OR LESS AS THE SYSTEM BOTH RUNS INTO THE COLD SURGE AND BECOMES PARKED IN A WEAK STEERING PATTERN ALOFT. IN TERMS OF INTENSITY THROUGH TAU 72, IN THE NEXT 12 HOURS OR SO, THE SYSTEM IS UNLIKELY TO INTENSITY MUCH, ESPECIALLY DUE TO ITS PROXIMITY TO LAND AND THE DISORGANIZED NATURE OF THE VORTEX. HOWEVER, ONCE IT MOVES OUT INTO THE OPEN WATERS NEAR THE POLILLO ISLANDS, IT IS EXPECTED TO RAPIDLY INTENSIFY TO AT LEAST 45 KNOTS, IN THE BRIEF PERIOD OF TIME PRIOR TO MAKING LANDFALL. THE SYSTEM WILL WEAKEN SIGNIFICANTLY AS IT CROSSES OVER THE RUGGED TERRAIN OF NORTHERN LUZON BUT QUICKLY REINTENSIFY AFTER MOVING INTO THE SOUTH CHINA SEA. TD 30W WILL THEN RAPIDLY INTENSITY ONCE MORE, REACHING A PEAK OF 70 KNOTS BY TAU 72 AS IT TAKES ADVANTAGE OF DRAMATICALLY IMPROVED OUTFLOW CONDITIONS. AFTER TAU 72, THE SYSTEM WILL FACE A RAPID INFLUX OF DRY AIR AS IT CONTINUES TO INTERACT WITH THE COLD SURGE, AND SHARPLY INCREASED SHEAR, LEADING TO A FAIRLY RAPID WEAKENING PHASE, WHICH WILL CONTINUE THROUGH THE REMAINDER OF THE FORECAST. DURING THIS TIME IN THE FORECAST, THE DEEP-LAYER STEERING PATTERN REMAINS VERY WEAK. HOWEVER, AS THE SYSTEM QUICKLY WEAKENS, IT WILL COME UNDER THE STEERING INFLUENCE OF THE LOW- TO MID-LEVEL FLOW, WHICH WILL BE FROM THE NORTHEAST. THIS WILL PUSH THE STEADILY WEAKENING TD 30W SOUTHWESTWARD AFTER TAU 72. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT THROUGH TAU 72, WITH ALL MEMBERS OF THE CONSENSUS PACKAGE INDICATING A NORTHWESTWARD TRACK, SLOWING AFTER TAU 48 AND REACHING AN INFLECTION POINT NEAR TAU 72. CROSS-TRACK SPREAD AT TAU 72 IS 95NM BETWEEN THE ECMWF ON THE NORTHERN EDGE AND THE EGRR ON THE SOUTH. ALONG-TRACK SPREAD IS MINIMAL TO TAU 48 BUT THEN BEGINS TO INCREASE, UP TO 100NM BY TAU 72. AT THIS POINT THE MODELS BEGIN TO SHOW SHARP DISAGREEMENTS, BOTH IN THE DIRECTION OF THE TRACK AND HOW FAST THE SYSTEM WILL MOVE. THE NAVGEM TAKES THE SYSTEM SLOWLY WESTWARD, REACHING THE EASTERN COAST OF HAINAN BY TAU 120, WHILE THE GFS IS ONE OF THE SLOWEST MODELS, ONLY REACHING A POSITION SOUTHEAST OF HAINAN BY TAU 120. THE ECMWF, EC-AIFS, AND GOOGLE DEEP MIND ARE FASTER, BUT ONLY REACHING A MIDPOINT BETWEEN THE GFS AND THE GEFS MEAN WHICH MAKES LANDFALL ALONG THE VIETNAMESE COAST BY TAU 120. THE RESULT IS A CROSS-TRACK ENVELOPE OF 265NM AND AN ALONG-TRACK SPREAD OF 230NM BY THE END OF THE FORECAST PERIOD. THE JTWC FORECAST IS POSITIONED NEAR THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD. INTENSITY GUIDANCE IS IN GOOD AGREEMENT, AND THE JTWC FORECAST IS POSITIONED CLOSE TO THE SHIPS TO TAU 36, THEN THE HAFS-A THEREAFTER. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN