WDPS31 PGTW 180900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09P (IRENE) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.0S 163.3E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 286 NM WEST OF PORT VILA, VANUATU MOVEMENT PAST 6 HOURS: EASTWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 20 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: THE LATEST ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND ENHANCED INFRARED (EIR) COMPOSITES SHOW TC 09P IS QUICKLY CONSOLIDATING AND BEGINNING TO DEVELOP A CENTRAL DENSE OVERCAST (CDO) FEATURE. AN 180523Z SSMIS 91GHZ MICROWAVE IMAGE REVEALED DEEP CONVECTIVE BANDING FEATURES, PARTICULARLY ACROSS THE SOUTHERN HEMISPHERE AND EXTENDING INTO THE EASTERN PORTIONS OF THE SYSTEM, WRAPPING INTO A DEVELOPING LOW LEVEL CIRCULATION CENTER (LLCC). HOWEVER, COMPARISON WITH THE 36GHZ IMAGERY SUGGESTS THE VORTEX IS TILTED TOWARDS THE SOUTHEAST, BASED ON A MODERATE NORTHWESTERLY SHEAR COMPONENT. THE INITIAL POSITION IS ASSESSED WITH LOW MEDIUM CONFIDENCE, A BIT SOUTH AND EAST OF THE PREPONDERANCE OF THE AGENCY FIX POSITIONS, USING THE MICROWAVE DATA. THE INITIAL INTENSITY IS INCREASED TO 40 KNOTS, HEDGED ABOVE THE AVAILABLE AGENCY FIXES BASED ON THE RAPID DEVELOPMENT OF THE CDO FEATURE AND OVERALL IMPROVED STRUCTURE SEEN IN THE MOST RECENT SATELLITE IMAGERY. CURRENTLY, THE ONLY OBJECTIVE INTENSITY ESTIMATE AVAILABLE IS THE OPEN-AIIR, WHICH IS RUNNING A BIT LOW AT AROUND 33 KNOTS. ANALYSIS REVEALS A FAVORABLE ENVIRONMENT WITH WARM SSTS OF 28-29C), LOW (10-15 KNOTS) NORTHWESTERLY VWS AND STRONG POLEWARD AND MODERATE EQUATORWARD OUTFLOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHWEST SIDE OF A NEAR-EQUATORIAL RIDGE (NER) CENTERED TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS KNES: T2.0 - 30 KTS PHFO: T2.5 - 35 KTS FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: MODERATE EQUATORWARD OUTFLOW. 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: TC 09P HAS SLOWED AND TAKEN A SLIGHTLY MORE EASTWARD JOG OVER THE PAST SIX HOURS THAN ORIGINALLY ANTICIPATED. THIS IS LIKELY A RESULT OF SOME VORTEX ASYMMETRY. HIGH RESOLUTION MODEL FIELDS HAVE CONSISTENTLY ANTICIPATED THE ASYMMETRY, BUT ALSO FORECASTED SYMMETRIZATION OVER THE NEXT 6 TO 12 HOURS. THE MOST RECENT BURST OF CONVECTIVE ACTIVITY AND LIGHTNING NEAR THE ASSESSED CENTER IS LIKELY AN INDICATION THIS PROCESS IS OCCURRING PRESENTLY. TC 09P WILL CONTINUE TO MOVE SOUTHEASTWARD ALONG THE WESTERN SIDE OF A DEEP NER CENTERED TO THE NORTH, PASSING BETWEEN VANUATU AND NEW CALEDONIA. CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE FOR THE NEXT 24 HOURS, ALLOWING FOR THE SYSTEM TO INTENSIFY UP TO A PEAK OF 55 KNOTS BY TAU 24. IF IT CAN SUCCESSFULLY ESTABLISH A SYMMETRIC LLCC AND A CDO, IT IS POSSIBLE THE SYSTEM COULD BRIEFLY REACH NEAR-TYPHOON STRENGTH, AS SOME OF THE GUIDANCE SUGGESTS. AROUND TAU 36, TRACK SPEEDS WILL INCREASE AS THE PRIMARY STEERING MECHANISM SHIFTS TO A BUILDING SUBTROPICAL RIDGE (STR) TO THE EAST. THE SYSTEM IS EXPECTED TO CROSS POLEWARD OF THE 26C ISOTHERM AND MOVE INTO STEADILY COOLER WATERS AS IT CONTINUES TREKKING SOUTHWARD. BY TAU 36, TC 09P BEGINS TO INTERACT WITH A DEEP 500MB TROUGH AND BEGINS TO EXPERIENCE AN INCREASE IN NORTHWESTERLY SHEAR, MARKING THE START OF SUBTROPICAL TRANSITION. THE SYSTEM IS EXPECTED TO RETAIN ITS WARM CORE CHARACTERISTICS BUT BECOMES STEADILY SHALLOWER AND MORE ASYMMETRIC IN NATURE AS IT WEAKENS AND MOVES SOUTHWARD. FULL TRANSITION TO A SUBTROPICAL CYCLONE IS EXPECTED NO LATER THAN TAU 72, BUT LIKELY CLOSER TO TAU 60. MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN VERY GOOD AGREEMENT ON THE GRACEFULLY ARCING SOUTHEASTWARD TRACK THROUGH THE DURATION OF THE FORECAST. AS THE SYSTEM UNDERGOES STT, MODEL GUIDANCE BEGINS TO SPREAD OUT TO A 240NM BY THE END OF THE FORECAST. THE JTWC FORECAST LIES ALONG THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE FOR THE FIRST 24 HOURS DUE TO THE RECENT MORE EASTWARD TRACK, BUT THEN TRACKS THE CONSENSUS MEAN THEREAFTER WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN GENERAL AGREEMENT ON THE INTENSIFICATION TREND, BUT SHOWS MODERATE SPREAD IN THE PEAK INTENSITY. THE HWRF, SOMEWHAT SURPRISINGLY, IS ON THE LOW END OF THE SPECTRUM, PEAKING THE SYSTEM AT JUST 45 KNOTS, WHILE THE COAMPS-TC (GFS) TAKES THE SYSTEM TO A 60 KNOT PEAK AT TAU 24, WITH ALL MODELS AGREEING ON RAPID WEAKENING AFTER THE PEAK AT TAU 24. THE JTWC FORECAST TRACKS JUST SLIGHTLY BELOW THE COAMPS-TC PEAK BUT THEN LIES A FEW KNOTS ABOVE THE CONSENSUS MEAN THROUGH THE REMAINDER OF THE FORECAST. CONFIDENCE IS MEDIUM DUE TO THE POSSIBILITY OF FASTER CONSOLIDATION, AND SYMMETRIZATION OF THE VORTEX AND THE RESULTANT FASTER INTENSIFICATION. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN