WDXS32 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 06S (ANGGREK) WARNING 
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.


SUMMARY:
   INITIAL POSITION: 10.1S 94.0E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 200 NM NORTHEAST OF COCOS ISLAND
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET


SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS TROPICAL
CYCLONE 06S (ANGGREK) HAS A PARTIALLY OBSCURED LOW LEVEL
CIRCULATION CENTER (LLCC) WITH MINIMAL CONVECTIVE OUTFLOW ALOFT
DRIFTING TO THE SOUTHWEST, REVEALING A VERTICAL TILT TO THE
SOUTHWEST WITH HEIGHT. ASYMMETRICAL SWATHS OF DEEP CONVECTION TO
THE NORTHWEST OF THE SYSTEM HIGHLIGHTS BANDING WRAPPING INTO THE
CIRCULATION. THE INITIAL POSITION WAS IDENTIFIED WITH LOW
CONFIDENCE BY HIMAWARI-9 ANIMATED VISIBLE IMAGERY AT 170550Z
REVEALING A SLIGHTLY OFFSET REGION OF CIRCULATION UNDER WEAK
UPPER-LEVEL OUTFLOW. THE INITIAL INTENSITY WAS ASSESSED WITH MEDIUM
CONFIDENCE, EXTRAPOLATED FROM A RCM-2 SAR PASS AT 162331Z DETAILING
50KT WINDS IN THE NORTHEAST QUADRANT OF THE STORM. DESPITE THE
DISORGANIZED UPPER-LEVEL OUTFLOW, THE LOWER LEVELS EXPOSE A TIGHT
CIRCULATION OF CLOUD BANDS. DEEP LAYER SHEAR IS LOW AT 10-15KTS,
BUT MID-LEVEL SHEAR APPEARS TO BE CUTTING OFF THE SYSTEM WITH GFS
MODEL SOUNDING SHOWING 15-20KTS EAST-NORTHEAST SHEAR IN THE 350-800
MB BAND. THE ENVIRONMENT IS MARGINALLY FAVORABLE AS SEA SURFACE
TEMPERATURES (SST) REMAIN IN THE 27-29C RANGE AND OVERALL SHEAR
REMAINS LOW. THE PRIMARY MITIGATING FACTOR AT THE MOMENT IS THE
DRY AIR FIRMLY ENSCONCED TO THE WEST. 


INITIAL WIND RADII BASIS: SAR DATA


CURRENT STEERING MECHANISM: RIDGE EXTENDING NORTH-SOUTH TO THE EAST
OF THE SYSTEM.


AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 45 KTS AT 170630Z
   CIMSS ADT: 37 KTS AT 170530Z


FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK WESTWARD


ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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 06S (ANGGREK) IS EXPECTED TO CONTINUE
TRACKING SOUTH RIDING THE EDGE OF A STRONG RIDGE TO THE EAST
THROUGH TAU 12. BETWEEN TAU 12-24, THE RIDGE TO THE EAST WILL BUILD
AND EXTEND WITH A STRONG GRADIENT TO THE SOUTH OF THE STORM,
STEERING THE SYSTEM TO THE SOUTH-SOUTHWEST THROUGH TAU 48. BY TAU
72, THE STORM IS EXPECTED TO TURN DUE WEST AS A RESULT OF BEING
BLOCKED TO THE NORTH BY THE NEAR EQUATORIAL RIDGE (NER), TO THE
EAST BY A TROUGH, AND TO THE SOUTH BY A RIDGE. SYSTEM INTENSITY IS
ANTICIPATED TO CONTINUE TO INCREASE THROUGH TAU 36 DUE TO FAVORABLE
SST (27-29C), LOW DEEP LAYER WIND SHEAR, MODEST RELATIVE HUMIDITY
LEVELS, AND SLIGHTLY IMPROVED UPPER-LEVEL OUTFLOW. THE PRIMARY
MITIGATING FACTOR PREVENTING THE SYSTEM FROM CONTINUING TO
INTENSIFY BEYOND TAU 36 IS THE DRY AIR THAT IS ANTICIPATED TO WRAP
INTO THE SYSTEM FROM THE WEST AND CONTINUE THROUGH THE FORECAST
PERIOD (TAU 120). MID LEVEL VERTICAL SHEAR IS ANTICIPATED TO
PERSIST IN THE 15-20 KT RANGE THROUGHOUT THE ENTIRE FORECAST
PERIOD, BUT IN THE EARLY PHASE OF THE FORECAST, THE SHEAR WILL BE
OFFSET BY THE OTHER FAVORABLE PARAMETERS, ALLOWING FOR A SHORT
PERIOD OF INTENSIFICATION. IN THE LONGER-TERM, THE COMBINED IMPACT
OF THE DRY AIR AND MID-LEVEL WIND SHEAR WILL LEAD TO A SLOW BUT
STEADY WEAKENING THROUGH THE END OF THE FORECAST PERIOD.


MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GENERAL
AGREEMENT THAT TC 06S (ANGGREK) WILL CONTINUE TO TRACK TOWARDS THE
SOUTH-SOUTHWEST, HOWEVER THERE IS A SPREAD OF THE TIMING AT WHICH
THE STORM WILL INFLUENCED BY THE STEERING OF THE RIDGE TO THE
SOUTH. AT TAU 24, THE JTWC CONSENUS MEMBER SHOW ONLY A 70NM
CROSS-TRACK SPREAD ALL HEADING TO THE SOUTH-SOUTHWEST BUT BEGIN TO
DISAGREE AND INCREASE TO 178 NM BY TAU 48 AS GFS BEGINS TO CUT THE
TURN TO THE WEST AND ECMWF CONTINUES POLEWARD. BY TAU 72, ALL
MEMBERS HEAD IN THE SAME GENERAL DIRECTION, DESPITE SHOWING
DIFFERING SPEEDS. THIS IS PRIMARILY DUE TO DISAGREEMENT IN THE
STRENGTH OF THE RIDGE TO THE SOUTH. CONSENSUS MEMBERS GENERALLY
AGREE THAT THE SYSTEM IS ANTICIPATED TO CONTINUE TO INTENSIFY
THROUGH TAU 24 AND BEGIN TO SUCCUMB TO THE AFFECTS OF DRY AIR
ENTRAINMENT BY TAU 36, GRADUALLY DECREASING TO 50KTS BY THE END OF
THE FORECAST PERIOD.


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