WDPS31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (GABRIELLE) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.1S 153.0E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 418 NM EAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND THE ENHANCED
INFRARED IMAGERY (EIR) DEPICT DEEP CENTRAL CONVECTION WITH
FORMATIVE BANDING WRAPPING AROUND AN OBSCURED LOW-LEVEL CIRCULATION
CENTER (LLCC). THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE
USING EXTRAPOLATION OF A BULLSEYE PASS FROM A 082244Z METOP-B ASCAT
IMAGE. THE INITIAL INTENSITY IS SET WITH HIGH CONFIDENCE BASED UPON
MULTIPLE AGENCY FIX ASSESSMENTS AND OBSERVATIONS FROM MARION REEF
WITH SUSTAINED WINDS OF 44 KNOTS (10-MINUTE AVERAGE). THE
ENVIRONMENTAL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH A
ROBUST POLEWARD OUTFLOW AND MODERATE EQUATORWARD OUTFLOW, WARM
SSTS, AND FAVORABLE (5-10 KNOTS) VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: SCATTEROMETER DATA FROM A 082244Z METOP-B
ASCAT

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T4.0 - 65 KTS
   ABRF: T3.5 - 55 KTS
   CIMSS ADT: 47 KTS AT 090000Z

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: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 12P WILL CONTINUE TRACKING SOUTHEASTWARD
ALONG THE WESTERN PERIPHERY OF THE STR. THE STR WILL BEGIN TO
REORIENT TO THE NORTHEAST DUE TO A DEEP TROUGH PROPAGATING OVER THE
CORAL SEA. THE IS EXPECTED TO DEEPEN OVER THE CORAL SEA AND HELP
ENHANCE THE POLEWARD OUTFLOW. THE SYSTEM WILL MOVE QUICKLY TO THE
SOUTHEAST ONCE THE STR BEGINS TO WEAKEN. THE SYSTEM WILL UNDERGO A
FEW CHANGES AS IT INTERACTS WITH AN APPROACHING SHORTWAVE TROUGH
FROM THE WEST AND A STRONG FINGER OF THE JET MAX TO THE SOUTH. DUE
TO THE ENHANCED POLEWARD OUTFLOW, THE SYSTEM INTENSIFIES
CONTINUALLY TO A PEAK OF 75 KNOTS BY TAU 36. SHORTLY AFTER TAU 36,
THE SYSTEM WILL BEGIN TO REACH COOLER WATER TEMPERATURES (24C-25C),
REDUCING THE INTENSITY AND HELPING AID IN THE SUBTROPICAL
TRANSITION DUE TO THE INTERACTION OF THE TROUGH AND DEEP LONGWAVE.
TC 12P WILL MAINTAIN TRACK TO THE SOUTHEAST AND COMPLETE THE
SUBTROPICAL TRANSITION BY TAU 72, IF NOT SHORTLY AFTER, AS THE
SYSTEM APPROACHES THE NORTHERN REGION OF NEW ZEALAND. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT 
WITH A MERE 60NM SPREAD AT TAU 12 AND ONLY SPREADS TO A MAXIMUM OF 
85NM THROUGH THE END OF THE FORECAST, LENDING HIGH CONFIDENCE TO THE 
JTWC FORECAST TRACK. CONFIDENCE IN THE OVERALL JTWC INTENSITY HAS 
INCREASED TO HIGH IN THE SHORT TERM FROM 0-72 HOURS AND MEDIUM IN THE 
LONG TERM AS THE PREVIOUS RAPID INTENSIFICATIONS (RI) ARE NO LONGER 
TRIGGERING. 

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