WDPS31 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (GABRIELLE) 
WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.2S 157.7E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 413 NM NORTHEAST OF BRISBANE, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 21 KTS
   SIGNIFICANT WAVE HEIGHT: 37 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
CONSOLIDATING SYSTEM WITH SPIRAL BANDS OF DEEP CONVECTION WRAPPING
INTO A CONVECTIVE CLOUD STRUCTURE, WHICH IS OBSCURING THE LOW-LEVEL
CIRCULATION CENTER (LLCC). MSI ALSO SHOWS MORE DEFINED CONVECTION
WRAPPING AROUND THE WESTERN PERIPHERY OF THE CIRCULATION. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 092225Z
BULLSEYE ASCAT-B PASS ALONG WITH AGENCY POSITION FIXES. THE INITIAL
INTENSITY IS SET WITH MEDIUM CONFIDENCE AND HEDGED SLIGHTLY LOWER 
THAN THE PGTW, KNES DVORAK ESTIMATES AND CLOSER TO ADT OF 77 KTS. 
ENVIRONMENTAL CONDITIONS REMAIN MARGINALLY FAVORABLE WITH MODERATE 
VERTICAL WIND SHEAR (VWS) OFFSET BY WARM SEA SURFACE TEMPERATURES 
(SSTS) AND STRONG POLEWARD OUTFLOW.

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 ADT: 77 KTS AT 092330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: OVER THE NEXT 12 HOURS ENVIRONMENTAL
CONDITIONS WILL REMAIN MARGINALLY FAVORABLE, CHARACTERIZED BY WARM
(26-27C) SEA SURFACE TEMPERATURES (SSTS), MODERATE POLEWARD OUTFLOW
OFFSET BY MODERATE (15-20 KNOTS) VERTICAL WIND SHEAR (VWS).
HOWEVER, THE VWS IS IN PHASE WITH THE DIRECTION OF THE STORMS MOTION 
RESULTING IN THE SHEAR BEING LESS OF AN INHIBITING FACTOR. TROPICAL 
CYCLONE 12P IS FORECAST TO TRACK SOUTHEASTWARD ALONG THE SOUTHWESTERN 
PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE EAST. 
ADDITIONALLY,
GIVEN THE MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED ABOVE THE
SYSTEM HAS A BRIEF WINDOW FOR FURTHER DEVELOPMENT BEFORE THE
SHORTWAVE TROUGH INDUCES INCREASED VERTICAL WIND SHEAR (VWS).
HOWEVER, 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 36. 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 VERY GOOD
AGREEMENT WITH 50NM SPREAD IN SOLUTIONS BY TAU 36, 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 SHOWING 
THE SYSTEM MAINTAINING ITS INTENSITY OVER THE NEXT 12 HOURS AS A 
RESULT OF WARM SSTS, STRONG POLEWARD OUTFLOW AND MODERATE VWS. AFTER 
TAU 12 ALL INTENSITY MODELS SHOW A GRADUAL WEAKENING TREND THROUGHOUT 
THE FORECAST PERIOD AS THE SYSTEM BECOMES FULLY SUBTROPICAL.  

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