Tropical Cyclone ROBYN (03S)

WTXS31 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 03S (ROBYN) WARNING NR 005//
RMKS/
1. TROPICAL CYCLONE 03S (ROBYN) WARNING NR 005    
   01 ACTIVE TROPICAL CYCLONE IN SOUTHIO
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   291200Z --- NEAR 18.8S 94.5E
     MOVEMENT PAST SIX HOURS - 140 DEGREES AT 12 KTS
     POSITION ACCURATE TO WITHIN 020 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
   RADIUS OF 034 KT WINDS - 070 NM NORTHEAST QUADRANT
                            055 NM SOUTHEAST QUADRANT
                            060 NM SOUTHWEST QUADRANT
                            045 NM NORTHWEST QUADRANT
   REPEAT POSIT: 18.8S 94.5E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   300000Z --- 19.3S 94.3E
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
    ---
REMARKS:
291500Z POSITION NEAR 18.9S 94.5E.
29NOV24. TROPICAL CYCLONE 03S (ROBYN), LOCATED APPROXIMATELY 420 NM
SOUTH-SOUTHWEST OF COCOS ISLANDS, AUSTRALIA, HAS TRACKED SOUTHEASTWARD
AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS THE SYSTEM HAS RAPIDLY ERODED AFTER IT DRIFTED 
INTO INCREASING (30KTS+) VERTICAL WIND SHEAR, COOL (25C) SST, AND COLD 
DRY AIR INTRUSION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE RAGGED, FULLY EXPOSED, AND ALMOST WASHED OUT LOW LEVEL
CIRCULATION IN THE MSI LOOP. THE INITIAL INTENSITY IS ALSO ASSESSED
WITH HIGH CONFIDENCE BASED ON AGENCY DVORAK AND AUTOMATED ESTIMATES
FROM CIMSS. ANALYSIS INDICATES A HIGHLY UNFAVORABLE ENVIRONMENT WITH
HIGH VWS, COOL SST, AND DRY AIR INTRUSION OFFSET ONLY BY STRONG 
POLEWARD OUTFLOW. THIS IS THE FINAL WARNING ON THIS SYSTEM BY THE 
JOINT TYPHOON WRNCEN PEARL HARBOR HI. THE SYSTEM WILL BE CLOSELY 
MONITORED FOR SIGNS OF REGENERATION. MINIMUM CENTRAL PRESSURE AT 
291200Z IS 999 MB. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 291200Z IS 12 
FEET.//
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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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