WDPS31 PGTW 210900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING NR 014// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.0S 137.8E INITIAL INTENSITY: 80 KTS GEOGRAPHIC REFERENCE: 405 NM EAST OF DARWIN, AUSTRALIA MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 26 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL CYCLONE 27P (NARELLE) WITH A FORMATIVE EYE FEATURE AND EXTREMELY COLD CLOUD TOPS WITHIN THE EASTERN SEMICIRCLE OF THE SYSTEM. THE SYMMETRY OF THE VORTEX HAS IMPROVED OVER THE PAST 6 HOURS, WITH CONVECTION NOW WRAPPING AROUND THE SOUTHERN SEMICIRCLE MORE PROMINENTLY. A 210432Z AMSR2 36 GHZ MICROWAVE IMAGE REVEALED A WELL-DEFINED MICROWAVE EYE FEATURE AT THE SURFACE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON EXTRAPOLATION FROM THE AMSR2 IMAGE, SUPPORTED BY ANIMATED RADAR IMAGERY FROM GOVE. THE INITIAL INTENSITY OF 80 KTS IS ASSESSED WITH MEDIUM CONFIDENCE, PRIMARILY SUPPORTED BY THE T4.5 AGENCY DVORAK FIXES FROM PGTW AND KNES. ENVIRONMENTAL ANALYSIS INDICATES THAT NARELLE IS CURRENTLY PLACED WITHIN A FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG EQUATORWARD OUTFLOW ALOFT, MODERATE (15-20 KTS) EASTERLY VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) POSITIONED OVER CENTRAL AUSTRALIA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS KNES: T4.5 - 77 KTS ABRF: T3.5 - 55 KTS CIMSS SATCON: 74 KTS AT 210600Z CIMSS ADT: 74 KTS AT 210600Z CIMSS AIDT: 74 KTS AT 210600Z CIMSS D-MINT: 58 KTS AT 210432Z CIMSS D-PRINT: 54 KTS AT 210600Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 27P IS FORECAST TO TRACK WEST-SOUTHWESTWARD, ALONG THE NORTHERN PERIPHERY OF A STR TO THE SOUTH THROUGH TAU 96. LANDFALL ALONG THE EASTERN COAST OF THE TOP END IS EXPECTED TO OCCUR IN ABOUT 6 HOURS, SOUTHWEST OF GOVE. TC NARELLE WILL THEN TRAVERSE ACROSS THE TOP END, SOUTH OF DARWIN, AND EMERGE OVER THE SOUTHERN PORTION OF THE BONAPARTE GULF AROUND TAU 42. NARELLE WILL THEN MAKE ANOTHER LANDFALL, NORTHWEST OF WYNDHAM, NEAR TAU 48 AND ONCE AGAIN EMERGE BACK OVER WATER, EAST OF ADELE ISLAND, JUST BEFORE TAU 72. THE SYSTEM WILL THEN CONTINUE ON A WEST-SOUTHWESTWARD TRAJECTORY THROUGH TAU 96 AS IT NEARS THE NORTHWESTERN EXTENT OF THE STR. AFTER TAU 96, NARELLE WILL TURN MORE SOUTHWESTWARD AS IT BEGINS A POLEWARD TRACK, AROUND THE RIDGE AXIS. REGARDING INTENSITY, NARELLE IS FORECAST TO ONLY HAVE ANOTHER 6 HOURS TO INTENSIFY BEFORE MAKING LANDFALL AND RAPIDLY WEAKENING. THE SYSTEM IS FORECAST TO DROP TO 35 KTS BY TAU 36 DUE TO TERRAIN INTERACTION, WHICH WILL THEN PERSIST THROUGH AROUND TAU 60, WHERE IT EMERGES BACK OVER WATER NEAR ADELE ISLAND. THE SYSTEM WILL THEN BEGIN TO RECUPERATE AFTER AN EXTENDED AMOUNT OF TIME OVER LAND AS IT TAKES ADVANTAGE OF A HIGHLY FAVORABLE ENVIRONMENT. RAPID INTENSIFICATION IS FORECAST TO OCCUR FROM TAU 96 TO 120 FROM 65 KTS TO 95 KTS AS STRONG POLEWARD OUTFLOW, LOW SHEAR, AND WARM SEA SURFACE TEMPERATURES ALLOW FOR SIGNIFICANT REDEVELOPMENT. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 WITH A CROSS-TRACK SPREAD OF JUST 55 NM AT TAU 72. ALONG-TRACK SPREAD HAS INCREASED THIS MODEL RUN, TO AROUND 160 NM AT TAU 72, WITH NAVGEM AND THE GFS ENSEMBLE MEAN BEING NOTABLY SLOWER THAN THE REMAINDER OF GUIDANCE. AFTER TAU 72, MODELS BEGIN TO DIFFER WITH SOME MODELS DEPICTING AN EXTENSION OF THE STR EXTENDING WESTWARD, KEEPING THE SYSTEM ON A MORE WESTWARD TRAJECTORY, WHILE OTHERS HAVE THE SYSTEM TURNING MORE SHARPLY POLEWARD. THE GFS AND ECMWF (AS WELL AS THEIR ENSEMBLE MEANS) DEPICT THE FORMER GROUPING WHILE THE AI MODELS DEPICTS THE LATTER GROUPING. CROSS-TRACK SPREAD AT TAU 120 OPENS UP TO OVER 300 NM. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE ENSEMBLE MEAN THROUGH TAU 72, THEN SLIGHTLY CLOSER TO THE AI MODELS THROUGH TAU 120. CONFIDENCE IS HIGH THROUGH TAU 72 AND MEDIUM THEREAFTER. INTENSITY GUIDANCE GENERALLY AGREES ON RAPID WEAKENING THROUGH TAU 36, A STEADY INTENSITY THROUGH TAU 60, AND QUICK REDEVELOPMENT AFTERWARD. HWRF IS THE MOST AGGRESSIVE MODEL AFTER TAU 60, SUGGESTING AN INTENSITY OF AROUND 105 KTS AT TAU 120. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE CONSENSUS THROUGH TAU 72, THEN CLOSER TO HWRF THROUGH TAU 120 DUE TO THE EXPECTED HIGHLY FAVORABLE ENVIRONMENT. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN