WDPS31 PGTW 092100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (GABRIELLE) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.7S 156.1E INITIAL INTENSITY: 75 KTS GEOGRAPHIC REFERENCE: 447 NM NORTH-NORTHEAST OF BRISBANE, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 16 KTS SIGNIFICANT WAVE HEIGHT: 34 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT CIRCULATION WITH A SOMEWHAT RAGGED APPEARANCE AS THE EYE FEATURE CONTINUES TO BE CLOUD-FILLED. EIR ALSO DEPICTS A BROAD CIRCULATION WITH CONVECTION SLIGHTLY DISPLACED POLEWARD AS OUTFLOW INCREASES AHEAD OF AN APPROACHING SHORTWAVE TROUGH. A 091655Z SSMIS 91GHZ MICROWAVE IMAGE REVEALS A COMPACT LLCC POSITIONED TO THE NORTHWEST EDGE OF A CURVED SPIRAL BAND. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE EIR IMAGE ALONG WITH THE AFOREMENTIONED 91GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS SET WITH MEDIUM CONFIDENCE AND HEDGED SLIGHTLY LOWER THAN THE PGTW, KNES DVORAK ESTIMATES AND CLOSER TO CMISS SATCON OF 78 KTS. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS KNES: T5.0 - 90 KTS CIMSS SATCON: 78 KTS AT 091452Z CIMSS ADT: 59 KTS AT 091730Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 15-20 KTS SST: 27-28 CELSIUS OUTFLOW: STRONG POLEWARD 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: TROPICAL CYCLONE 12P IS FORECAST TO TRACK SOUTHEASTWARD ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE EAST. BY TAU 12, THE SYSTEM IS EXPECTED TO ACCELERATE AS THE SYSTEM MOVES INTO ENHANCED FLOW BETWEEN AN APPROACHING SHORTWAVE TROUGH AND THE STR TO THE EAST. ADDITIONALLY, THE SYSTEM HAS A BRIEF WINDOW FOR FURTHER DEVELOPMENT BEFORE THE SHORTWAVE TROUGH INDUCES INCREASED VERTICAL WIND SHEAR (VWS). AFTER TAU 24, THE COMBINATION OF INCREASED VWS AND COOLER WATERS WILL ULTIMATELY RESULT IN A GRADUAL WEAKENING TREND. FURTHERMORE, TC 12P WILL INTERACT WITH THE SHORTWAVE TROUGH AND BEGIN SUBTROPICAL TRANSITION THROUGH TAU 48. THE SUBTROPICAL TRANSITION WILL RESULT IN AN ASYMMETRICAL WARM-CORE WITH A LARGER WIND FIELD AS THE SYSTEM TRACKS NEAR NEW ZEALAND. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT WITH 90NM SPREAD IN SOLUTIONS BY TAU 48, LENDING HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. ADDITIONALLY, BOTH GFS AND ECMWF ENSEMBLE MEMBERS ARE IN GOOD AGREEMENT WITH VERY LITTLE TRACK SPREAD. THE RELIABLE INTENSITY GUIDANCE IS IN FAIR AGREEMENT AND SUPPORTS A BRIEF INCREASE IN INTENSITY OVER THE NEXT 12 HOURS AS A RESULT OF STRONG POLEWARD OUTFLOW AND MODERATE VWS. AFTER TAU 24 ALL INTENSITY MODELS SHOW A GRADUAL WEAKENING TREND THROUGHOUT THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN