WDPS31 PGTW 230300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (EIGHTEEN) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.0S 151.8E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 388 NM EAST-NORTHEAST OF CAIRNS, AUSTRALIA MOVEMENT PAST 6 HOURS: EASTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 22 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SYMMETRICAL BALL OF DEEP CONVECTION, WITH OVERSHOOTING TOPS AND FREQUENT INNER-CORE LIGHTNING BURSTS. CLOUD TOP TEMPERATURES IN THE OVERSHOOTING TOPS WERE COLDER THAN -90C A BIT EARLIER BUT THE LATEST ENHANCED INFRARED IMAGERY SHOWS THE CLOUD TOPS WARMING A BIT OVERALL AND A REDUCTION IN LIGHTNING ACTIVITY. A 222335Z GMI 37GHZ MICROWAVE PASS REVEALED A NASCENT MICROWAVE EYE, ALTHOUGH THE SURROUNDING BANDING FEATURES WERE QUITE SHALLOW AND THE CONVECTION IS DISPLACED TO THE SOUTHEAST DUE TO SOME MODERATE WEST-NORTHWESTERLY SHEAR IN THE MID-LEVELS. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE DEVELOPING MICROWAVE EYE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED HIGHER THAN MOST OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED ABOVE IN LIGHT OF TWO FACTORS. FIRST, A 222216Z ASCAT-B ULTRA-HIGH RESOLUTION WINDSPEED PRODUCT WHICH SHOWED A BAND OF ELEVATED WINDS EXTENDING FROM SOUTH OF THE CIRCULATION UP THE WEST SIDE AND BEGINNING TO WRAP INTO THE NORTHERN PORTION OF THE LLCC, AND MAXIMUM WINDS OF UP TO 45 KNOTS. SECOND, A PARTIAL 221938Z RCM-2 SAR PASS SHOWED A VERY SIMILAR WIND STRUCTURE OVERALL, WITH EVEN HIGHER WINDS UP TO NEAR 60 KNOTS, WHICH WHILE PROBABLY ABOUT 10 KNOTS TOO HIGH, STILL PROVIDE AMPLE SUPPORT FOR A 50 KNOT INTENSITY. THE ENVIRONMENT IS FAVORABLE FOR ADDITIONAL INTENSIFICATION, POTENTIALLY RAPID INTENSIFICATION (RI) WITH LOW VWS, VERY WARM SSTS AND ROBUST POLEWARD AND EQUATORWARD OUTFLOW ALOFT. INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA. CURRENT STEERING MECHANISM: SOUTH-SOUTHWESTERN PERIPHERY OF A DEEP-LAYER NEAR EQUATORIAL RIDGE (NER) NORTHEAST OF THE SOLOMON ISLANDS. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS KNES: T2.0 - 30 KTS ABRF: T2.5 - 35 KTS CIMSS ADT: 51 KTS AT 230000Z CIMSS AIDT: 38 KTS AT 230000Z CIMSS D-MINT: 33 KTS AT 222323Z CIMSS D-PRINT: 31 KTS AT 230030Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD OTHER FACTORS: LLCC REMAINS ELONGATED NORTHWEST-SOUTHEAST. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 18P HAS ALREADY TURNED ONTO A MORE EASTWARD TRACK THAN ORIGINALLY ANTICIPATED, WITH THE ORIENTATION OF THE NER BECOMING MORE EAST-WEST. THE SYSTEM WILL CONTINUE ON A GENERALLY EASTWARD TRACK FOR ABOUT THE NEXT 12 HOURS BEFORE TURNING POLEWARD BY TAU 24. THE STEERING RIDGE IS EXPECTED TO SLOWLY SHIFT EASTWARD AND STRETCH OUT BUT IN DOING SO WILL WEAKEN THE STEERING GRADIENT AS WELL, LEADING TO A SLOW DOWN IN TRACK SPEEDS AS THE SYSTEM TURNS POLEWARD. BY TAU 48, A DEVELOPING TROPICAL CYCLONE NEAR VANUATU WILL BEGIN TO MOVE RAPIDLY POLEWARD, AND THE RIDGE WILL ONCE AGAIN STRENGTHEN, EXTENDING ALL THE WAY FROM THE SOLOMONS TO SOUTHEAST OF SAMOA, WITH A SEPARATE CELL FORMING NEAR VANUATU. TC 18P WILL ACCELERATE SOUTHWARD ALONG THE WESTERN SIDE OF THIS RIDGE FROM TAU 48 THROUGH THE REMAINDER OF THE FORECAST PERIOD. IN TERMS OF INTENSITY, THE LLCC REMAINS SOMEWHAT ELONGATED AND THERE IS STILL A FAIR AMOUNT OF VORTEX TILT, SO THE RATE OF INTENSIFICATION WILL BE RATHER SLOW IN THE FIRST 12 HOURS OF THE FORECAST. THE PACE WILL PICK UP AFTER TAU 12, AS THE VORTEX ALIGNS AND SYMMETRIZES, AND THE SYSTEM TAPS INTO A STRONG POLEWARD OUTFLOW CHANNEL. THE CURRENT PEAK LOOKS TO BE AROUND 90 KNOTS BUT SOME OF THE RI GUIDANCE SUGGESTS A POTENTIAL PEAK UP TO 30 KNOTS HIGHER THAN THAT. GENERALLY SPEAKING, THE ENVIRONMENT WILL REMAIN HIGHLY FAVORABLE FOR RI TO COMMENCE ONCE THE SYMMETRIZATION PROCESS OCCURS. THE SYSTEM WILL PEAK BETWEEN TAU 48 AND TAU 72, BEFORE RAPIDLY INCREASING SHEAR WILL BEGIN TO IMPACT THE SYSTEM AND START THE GENERAL WEAKENING TREND WHICH WILL CONTINUE THROUGH THE END OF THE FORECAST PERIOD. MODEL DISCUSSION: ALL MEMBERS OF THE CONSENSUS PACKAGE AGREE ON THE OVERALL SHAPE OF THE FORECAST TRACK BUT DO DIFFER ON THE SHARPNESS OF THE TURN AND THE SPEED OF ADVANCE, PARTICULARLY AFTER TAU 48. THE GFS AND GEFS MEAN REMAIN THE EASTERN OUTLIERS, WHILE NAVGEM AND ECMWF MARK THE WESTERN SIDE OF THE GUIDANCE ENVELOPE. ECEPS CONTINUES TO SHOW A VERY WIDE SPREAD IN POTENTIAL TRACKS, FROM EASTERN AUSTRALIA TO NEW CALEDONIA. THE GEFS HAS TIGHTENED UP A BIT BUT STILL SHOWS A HIGH DEGREE OF UNCERTAINTY. THE JTWC FORECAST TRACKS THE CONSENSUS MEAN TO TAU 48, THEN RIDES JUST INSIDE, OR WEST, OF THE MEAN THROUGH THE REMAINDER OF THE FORECAST PERIOD. INTENSITY GUIDANCE IS SOMEWHAT MIXED, WITH THE COAMPS-TC KEEPING THE SYSTEM AT 50 KNOTS ALL THE WAY THROUGH TAU 120, WHILE THE HAFS-A AND HWRF DEPICT SLOW INTENSIFICATION THROUGH TAU 24, THEN STEADILY INTENSIFY THE SYSTEM ALL THE WAY THROUGH TAU 120 WHERE THEY PEAK AROUND 105 KNOTS. THE SHIPS OUTPUT AND THE CONSENSUS MEAN MOST CLOSELY RESEMBLE THE JTWC FORECAST, WHICH IS ABOUT 10 KNOTS HIGHER THAN THE MEAN. ADDITIONALLY, RIPA, RICN, FRIA AND RI25 THROUGH RI55 RI AIDS ARE ALL TRIPPED WITH THIS MODEL RUN, PEAKING BETWEEN 105 AND 120 KNOTS BY TAU 48. THE JTWC FORECAST DOES FOLLOW THE LOWER RI AIDS SUCH AS RI25 AND RI30 BUT IS SHALLOWER THAN THE MORE AGGRESSIVE RIPA, RICN AND FRIA. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN