WDPS31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (GABRIELLE) 
WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0S 152.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 402 NM EAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 12Ps PROGRESSION TO THE SOUTHEAST HAS SLOWED
CONSIDERABLY AS THE SYSTEM WRAPS TIGHTER AROUND THE LOW-LEVEL
CIRCULATION CENTER (LLCC) AS SEEN ON THE ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY. THE LLCC CENTER REMAINS WELL-DEFINED JUST
NORTH OF LIHOU REEF WITH 17 KNOTS SUSTAINED WINDS (10-MINUTE
AVERAGE) REMAINING OUT OF THE SOUTHEAST, WHILE AT MARION REEF
EASTERLY WINDS ARE REPORTING SOUTHEASTERLY AT 37 KNOTS SUSTAINED
(10-MINUTE AVERAGE). THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON A NEAR MICROWAVE EYE AS DISPLAYED ON A 081707Z
SSMIS 37GHZ IMAGE. THE INITIAL INTENSITY IS HEDGED SLIGHTLY HIGHER
AND SET WITH MEDIUM CONFIDENCE BASED UPON MULTIPLE AGENCY FIXES IN
THE T3.0-45KTS RANGE. ANALYSIS INDICATES A FAVORABLE ENVIRONMENT
WITH A ROBUST POLEWARD OUTFLOW AND MODERATE EQUATORWARD OUTFLOW,
WARM SSTS, AND FAVORABLE (5-10 KNOTS) VERTICAL WIND SHEAR.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   ABRF: T3.0 - 45 KTS
   CIMSS SATCON: 51 KTS AT 081510Z
   CIMSS ADT: 37 KTS AT 081730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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: TC 12P WILL TRACK SOUTHEASTWARD ALONG THE
WESTERN PERIPHERY OF THE STR. OVER THE NEXT SEVERAL HOURS, THE STR
WILL REORIENT TO THE NORTHEAST DUE TO A DEEP TROUGH PROPAGATING
OVER THE CORAL SEA. AS THE TROUGH DIGS INTO THE REGION, IT WILL
HELP INCREASE POLEWARD OUTFLOW AND THE OVERALL NET MOTION
OF THE SYSTEM BETWEEN THE TROUGH AND STR. ONCE ON THE SOUTHEAST
TRACK AND BETWEEN TAUS 36 AND 48, THE SYSTEM WILL UNDERGO A FEW
CHANGES AS IT INTERACTS WITH AN APPROACHING SHORTWAVE TROUGH FROM
THE WEST. THE FIRST CHANGE WILL BE FROM ENHANCED POLEWARD OUTFLOW,
INCREASING THE INTENSITY TO A PEAK OF 75 KNOTS. THE SECOND CHANGE
WILL BEGIN TO OCCUR BY TAU 48, AS THE SYSTEM REDUCES INTENSITY AS
IT UNDERGOES SUBTROPICAL TRANSITION DUE TO THE INTERACTION OF THE
TROUGH AND DEEP LONGWAVE. AS TC 12P CONTINUES ON THE SOUTHEAST
TRACK, IT WILL CONTINUE TO TRANSITION AND COMPLETE BY TAU 96 AS IT
APPROACHES THE NORTHERN REGION OF NEW ZEALAND. NEAR TAUS 72 AND 96,
THE SYSTEM WILL UNDERGO THE MOST CHANGE AS THE SUBTROPICAL JET
INCREASES TO 40 TO 60 KNOTS AND THE SSTS COOLS SIGNIFICANTLY FROM
24 TO 22C.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT WITH A MERE 85NM SPREAD IN SOLUTIONS FROM TAU 48 THROUGH
THE END OF THE FORECAST, LENDING HIGH CONFIDENCE TO THE JTWC
FORECAST TRACK. THERE IS ONLY MEDIUM CONFIDENCE IN THE OVERALL JTWC
INTENSITY AS THERE REMAIN SOME INDICATIONS OF POTENTIAL RAPID
INTENSIFICATION (RI) WITHIN THE NEXT 24 TO 36 HOURS WITH PEAK
PROBABILITIES OF 25 TO 45 PERCENT THROUGH TAU 24. ADDITIONALLY, RAPID 
INTENSIFICATION AIDS ARE REFLECTING A CONDUCIVE RI ENVIRONMENT 
CHARACTERIZED BY ROBUST POLEWARD OUTFLOW, LOW VERTICAL WIND SHEAR, AND 
WARM SST VALUES. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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