WDXS31 PGTW 281500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 03S (ROBYN) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.4S 91.1E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 420 NM SOUTHWEST OF COCOS ISLANDS,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS
SLIGHTLY IMPROVED AS INDICATED BY OVERSHOOTING CLOUD TOPS AND THE
FORMATION OF A MINIMUM CLOUD WEDGE ALONG THE SOUTHEASTERN QUADRANT IN 
THE CENTRAL CLOUD COVER. THE INITIAL POSITION IS PLACED WITH MEDIUM 
CONFIDENCE BASED ON A LOW LEVEL CIRCULATION CENTER (LLCC) FEATURE IN 
THE 281057Z TROPICS PASSIVE MICROWAVE IMAGE. THE INITIAL INTENSITY IS 
ALSO PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM RECENT 
SCATTEROMETER DATA AND OVERALL ASSESSMENT OF AGENCY DVORAK AND 
AUTOMATED ESTIMATES. ANALYSIS INDICATES A MARGINAL ENVIRONMENT WITH 
WARM SST AND STRONG POLEWARD OUTFLOW OFFSET BY STRONG VWS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA.

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) DIRECTLY TO
THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 59 KTS AT 281130Z
   CIMSS AIDT: 47 KTS AT 281130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 03S IS EXPECTED TO CONTINUE SOUTH-
SOUTHEASTWARD UNDER THE NER. AFTER TAU 12, A SUBTROPICAL RIDGE 
APPROACHING FROM THE SOUTHWEST WILL COMPETE FOR STEERING, SLOW DOWN 
THE STORM MOTION, THEN DRIVE THE CYCLONE WESTWARD AFTER TAU 24. THE 
MARGINAL ENVIRONMENT WILL SUSTAIN THE CURRENT INTENSITY UP TO TAU 12; 
AFTERWARD, INCREASING VWS AND COOLING SST WILL GRADUALLY ERODE THE 
SYSTEM TO DISSIPATION BY TAU 48.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT WITH 
A GRADUAL SPREAD TO 135NM BY TAU 48; HOWEVER, GIVEN THE UNCERTAINTIES
WITH THE TRANSITION TO A SECONDARY STEERING MECHANISM, THERE IS
ONLY MEDIUM CONFIDENCE TO THE JTWC TRACK AND INTENSITY FORECASTS.  

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