WDXS31 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 03S (ROBYN) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.4S 92.5E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 1324 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE 03S PEAKED AT 55 KNOTS NEAR 281500Z AS EVIDENCED BY 
A 281516Z ASCAT-C UHR IMAGE SHOWING 50-55 KNOTS OVER THE NORTHERN 
SEMICIRCLE. OVER THE PAST SIX HOURS, ANIMATED ENHANCED INFRARED (EIR) 
SATELLITE IMAGERY REVEALS RAPID WEAKENING DUE TO STRONG VERTICAL WIND 
SHEAR AND SIGNIFICANT MID-LEVEL DRY AIR ENTRAINMENT. A 282352Z WSF-M 
89GHZ COLOR COMPOSITE MICROWAVE IMAGE SHOWS ISOLATED DEEP CONVECTION 
SHEARED 160NM SOUTHEAST OF THE CENTER, WITH SHALLOW BANDING WRAPPING 
TIGHTLY INTO A DEFINED LOW-LEVEL CIRCULATION CENTER. THE INITIAL 
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE WSF-M IMAGE. 
THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE 
BASED ON A BLEND OF DVORAK FINAL-T ESTIMATES RANGING FROM T2.0-2.5 
(30-35 KNOTS) AND THE MORE CONSERVATIVE CURRENT INTENSITY ESTIMATES 
OF 3.5 (SEE BELOW).

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: LOW-LEVEL TO MID-LEVEL STEERING RIDGE
POSITIONED TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.5 - 55 KTS
   APRF: T3.5 - 55 KTS
   CIMSS ADT: 59 KTS AT 282330Z
   CIMSS AIDT: 45 KTS AT 282330Z
   CIMSS D-MINT: 60 KTS AT 281853Z
   CIMSS D-PRINT: 34 KTS AT 290000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 35-40 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR ENTRAINMENT

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: TROPICAL CYCLONE (TC) 03S IS EXPECTED TO
RAPIDLY WEAKEN THROUGH THE FORECAST PERIOD UNDER STRONG NORTHWESTERLY 
VERTICAL WIND SHEAR (VWS) AND SIGNIFICANT DRY AIR ENTRAINMENT. THE 
SYSTEM WILL CONTINUE TRACKING GENERALLY SOUTHEASTWARD THROUGH TAU 12 
ALONG THE SOUTHWEST PERIPHERY OF A LOW-LEVEL TO MID-LEVEL STEERING 
RIDGE. AS 03S WEAKENS AND BECOMES SHALLOWER, IT WILL SLOW AND TURN 
WESTWARD UNDER THE STEERING INFLUENCE OF A LOW-LEVEL HIGH TO THE 
SOUTH, WITH DISSIPATION ANTICIPATED BY TAU 36 DUE TO EXTENSIVE DRY 
AIR AND STRONG VWS.     
 
MODEL DISCUSSION: ALTHOUGH THERE IS SOME UNCERTAINTY IN THE TIMING
OF THE SHARP WESTWARD TURN, DETERMINISTIC MODEL GUIDANCE REMAINS IN
FAIR AGREEMENT WITH A 90NM CROSS-TRACK SPREAD IN SOLUTIONS AT TAU
36. ADDITIONALLY, THE GEFS AND EPS ENSEMBLES SUPPORT THE JTWC TRACK
AND INTENSITY FORECAST WITH MEDIUM CONFIDENCE.  

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