WDPS31 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (GABRIELLE) 
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.9S 153.9E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 478 NM EAST-SOUTHEAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) INDICATES THAT TC
GABRIELLE CONTINUES TO CONSOLIDATE AND INTENSIFY, THOUGH THE SYSTEM
REMAINS VERY COMPACT. BOTH A 090342Z ATMS 183GHZ AND 090539Z SSMIS
36GHZ MICROWAVE IMAGE SHOWED A NASCENT EYEWALL AND DEVELOPING
MICROWAVE EYE FEATURE. ANIMATED ENHANCED INFRARED (EIR) IMAGERY
THROUGH THE 0700Z HOURS SHOWS THE SYSTEM IS LIKELY EMBARKING ON A
PERIOD OF RAPID INTENSIFICATION, WITH HOT TOWERS FIRING OFF AROUND
A NASCENT EYE FEATURE. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE MICROWAVE EYE FEATURE IN THE AFOREMENTIONED
SSMIS IMAGE. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE CONGRUENCE OF AGENCY CURRENT INTENSITY ESTIMATES, RAW
ADT VALUES APPROACHING T4.0 AND AN OPEN-AIIR ESTIMATE OF
APPROXIMATELY 65 KNOTS. THE SYSTEM IS NOW BEGUN TO PICK UP SPEED AS
IT TRACKS ALONG THE STRONG GRADIENT BETWEEN A SUBTROPICAL RIDGE
(STR) TO THE EAST AND AN APPROACHING DEEP TROUGH CURRENTLY OVER
EASTERN AUSTRALIA. ENVIRONMENTAL CONDITIONS ARE CURRENTLY
FAVORABLE, WITH WARM SSTS, LOW (10-15 KTS) VWS AND ROBUST POLEWARD
OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SCATTEROMETER
DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   ABRF: T3.5 - 55 KTS
   CIMSS SATCON: 69 KTS AT 090342Z
   CIMSS ADT: 57 KTS AT 090530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: HAVING MADE THE TURN OVER TO THE SOUTHEAST
OVER THE PAST DAY, TC 12P HAS NOW BEGUN TO PICK UP SPEED, AS THE
GRADIENT BETWEEN THE STR TO THE EAST AND THE TROUGH TO THE WEST
STRENGTHENS. THE SYSTEM IS FORECAST TO CONTINUE TO ACCELERATE ON
THE SOUTHEASTWARD TRACK OVER THE NEXT 36 HOURS. AFTER TAU 36, THE
SYSTEM IS EXPECTED TO SLOW AS THE SYSTEM MOVES UNDER THE
UPPER-LEVEL TROUGH AND THE STR WEAKENS AND SLIDES NORTHWESTWARD. IN
TERMS OF INTENSITY, TC 12P HAS ABOUT ANOTHER 24 HOURS OF GOOD
CONDITIONS IN WHICH TO INTENSIFY, WITH WARM SSTS, LOW VWS AND
INCREASING POLEWARD OUTFLOW. PEAK INTENSITY OF AT LEAST 80 KNOTS IS
EXPECTED BY AROUND TAU 24. SHORTLY AFTER THE SYSTEM REACHES PEAK
INTENSITY, IT WILL BEGIN A RAPID SUBTROPICAL TRANSITION (STT).
AROUND TAU 30, TC 12P WILL CROSS THE 26C ISOTHERM AND BEGIN TO FEEL
THE EFFECTS OF MID-LEVEL DRY AIR ENTRAINMENT, WHICH WILL RAPIDLY
CONFINE THE WARM-CORE TO BELOW 500MB, LEADING TO RAPID WEAKENING
DURING THE STT. TC 12P IS FORECAST TO COMPLETE TRANSITION TO A
LARGE, STORM-FORCE SUBTROPICAL LOW BY TAU 48, AS IT TRACKS TOWARDS
THE NORTH ISLAND OF NEW ZEALAND. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
VERY GOOD AGREEMENT ON THE TRACK FORECAST, WITH ALL MODELS ENCASED
WITHIN A VERY SMALL ENVELOPE. THE JTWC FORECAST TRACKS CLOSE TO THE
CONSENSUS MEAN, RIGHT DOWN THE MIDDLE OF THE TIGHT ENVELOPE, WITH
HIGH CONFIDENCE. INTENSITY GUIDANCE IS A BIT MORE MIXED, WITH THE
30-KNOT SPREAD IN THE PEAK INTENSITY. THE RIPA RAPID
INTENSIFICATION (RI) AID IS THE MOST AGGRESSIVE OF THE GUIDANCE
MEMBERS, SHOWING A PEAK NEAR 90 KNOTS BY TAU 24, WHILE THE HWRF IS
THE WEAKEST MEMBER, INDICATING A PEAK OF JUST 65 KNOTS AT THE SAME
TIME. THE REMAINDER OF THE DETERMINISTIC GUIDANCE FALLS ROUGHLY
BETWEEN THE TWO EXTREMES. THE COAMPS-TC ENSEMBLE PROBABILITY
FORECASTS CALLS FOR A 50 PERCENT CHANCE OF RI WITHIN THE FIRST 24
HOURS, WHICH SUPPORTS THE GFS-BASED RIPA. ALL GUIDANCE SHOWS A
WEAKENING TREND AFTER TAU 24, BUT WITH A FAIRLY LARGE SPREAD IN THE
PACE OF WEAKENING. THE JTWC FORECAST FOLLOWS RIPA FOR THE FIRST 12
HOURS BUT PEAKS ABOUT 10 KNOTS LOWER, THEN DEVIATES LOWER THAN THE
CONSENSUS THROUGH THE STT PHASE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
NNNN