WDXS32 PGTW 230900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 06S (ANGGREK)    
WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.0S 91.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 1182 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 06S HAS MAINTAINED INTENSITY AT 40 KNOTS DUE
PRIMARILY TO UPWELLING COOLER WATER RESULTING FROM THE SYSTEM'S
SLOW TRACK MOTION AS REVEALED IN THE RECENT HAFS-A SST ANALYSIS.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
FRAGMENTED, WEAK DEEP CONVECTIVE BANDING WRAPPING INTO A RAGGED
LOW-LEVEL CIRCULATION CENTER (LLCC), WHICH SUPPORTS THE INITIAL
POSITION WITH HIGH CONFIDENCE. A 230342Z MHS 89 GHZ MICROWAVE IMAGE
SHOWS A 100-110 NM DIAMETER CONVECTION-FREE CORE WITH DEEP
CONVECTIVE BANDS WRAPPED LOOSELY. A 230258Z ASCAT-B BULLSEYE IMAGE
SHOWS A DEFINED CENTER WITH 30-35 KNOT WINDS OVER THE EASTERN
SEMICIRCLE, WHICH SUPPORTS THE INITIAL WIND RADII WITH HIGH
CONFIDENCE. ANIMATED WATER VAPOR IMAGERY AND RECENT CIMSS
UPPER-LEVEL WINDS SHOW AN UPPER-LEVEL TROUGH IMPINGING ON THE
SOUTHERN PERIPHERY OF THE SYSTEM, LIMITING POLEWARD OUTFLOW, WITH
MODERATE EQUATORWARD OUTFLOW. THE INITIAL INTENSITY OF 40 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON RECENT ASCAT DATA AS WELL AS
THE PGTW, DEMS AND APRF SUBJECTIVE DVORAK ESTIMATES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A
NEAR-EQUATORIAL RIDGE (NER) POSITIONED TO THE NORTH AND A WEAK
SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T2.5 - 35 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 52 KTS AT 230417Z
   CIMSS ADT: 45 KTS AT 230530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: UPWELLING COOLER WATER

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: TRACK MOTION IS EXPECTED TO REMAIN SLOW AND
POSSIBLY ERRATIC UNTIL AFTER TAU 24 WHEN A DOMINANT STR IS
FORECASTED TO BUILD TO THE SOUTH AND THEN SOUTHEAST, WHICH WILL
ACCELERATE THE SYSTEM WEST-SOUTHWESTWARD THROUGH THE FORECAST
PERIOD. AS THE SYSTEM ACCELERATES, THE LIMITING EFFECTS OF THE
UPWELLING COOLER WATER WILL LESSEN AND THE SYSTEM WILL INTENSIFY AT A
FASTER RATE UP TO A PEAK INTENSITY OF 70-75 KNOTS. AFTER TAU 72,
ENVIRONMENTAL CONDITIONS WILL DEGRADE SLIGHTLY WITH SOME DRY AIR
ENTRAINMENT AND WEAKER OUTFLOW RESULTING IN A SLIGHT WEAKENING TREND. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 72 WITH A 65 NM CROSS-TRACK SPREAD IN SOLUTIONS AT TAU
72 DIVERGING THROUGH TAU 120. THE 230000Z GFS AND ECMWF ENSEMBLES
ALSO SHOW A SIMILAR SPREAD. INTENSITY GUIDANCE REMAINS IN FAIR
AGREEMENT THROUGH THE FORECAST PERIOD, LENDING MEDIUM OVERALL
CONFIDENCE TO THE JTWC INTENSITY FORECAST. 

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