WDXS32 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 06S (ANGGREK) WARNING 
NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.0S 92.2E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 175 NM EAST OF COCOS ISLAND
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS
QUASI-STATIONARY TROPICAL CYCLONE (TC) 06S (ANGGREK) TRANSITING
WEST-NORTHWESTWARD AT 2 KTS. BANDS OF MID- AND LOWER- LEVEL
MOISTURE WRAP INTO THE CENTER OF THE STORM, HOWEVER THE LOWER-LEVEL
CIRCULATION CENTER IS OBSCURED BY DEEP LAYER CONVECTION AND WEAK
OUTFLOW DRIFTING OUT OF THE WESTERN SEMICIRCLE OF THE STORM. A
WEST-NORTHWEST TILT WITH HEIGHT IS SUPPORTED BY A CIMSS SHEAR
ANALYSIS REFLECTING UP TO 21KTS OF VERTICAL WIND SHEAR FROM THE
EAST. SEA SURFACE TEMPERATURE (SST) IS ESTIMATED TO BE BETWEEN
27-28C SUPPORTING TC DEVELOPMENT. DRY AIR ENTRAINMENT FROM THE
NORTHEAST IS REPRESENTED IN MSI SHOWING A WEDGE OF CLEAR SKIES TO
THE EAST OF THE CENTER. THE INITIAL POSITION WAS EXTRAPOLATED WITH
MEDIUM CONFIDENCE BASED ON A 210336Z METOP-C ASCAT IMAGE DEPICTING
A CLEAR EYE, DESPITE AN INDETERMINATE LLCC IN THE MSI. THE INITIAL
INTENSITY WAS ASSESSED WITH MEDIUM CONFIDENCE BASED ON PERSISTENCE
FROM A 202332Z RCM-3 SAR PASS REPRESENTING MAXIMUM WINDS BETWEEN
73-80KTS.

INITIAL WIND RADII BASIS: SAR AND SCATTEROMETER DATA. 

CURRENT STEERING MECHANISM: THE NORTHEASTERN PERIPHERY OF A
BUILDING RIDGE TO THE SOUTHWEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T3.0 - 45 KTS
   APRF: T3.5 - 55 KTS
   CIMSS SATCON: 59 KTS AT 0700Z
   CIMSS ADT: 61 KTS AT 210530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 06S (ANGGREK) IS FORECAST TO TRANSIT AT
2KTS TO THE WEST THROUGH TAU  12, DRIVEN BY A BUILDING RIDGE TO THE
SOUTHWEST. FROM TAU 24-48, THE SYSTEM IS ANTICIPATED TO GRADUALLY
CURVE FROM A WEST-SOUTHWEST AT 2KTS TRACK TO A SOUTHWEST TRACK
BEFORE CONTINUING TO THE SOUTHWEST AT 5KTS THROUGH THE END OF THE
FORECAST PERIOD (TAU 120). THE TRANSITION FROM WEST-SOUTHWEST TO
SOUTHWEST IS STEERED FIRST TOWARDS A WEAKNESS IN THE STR TO THE
SOUTH, THEN ALONG THE WESTERN SIDE OF THE STR AS IT SHIFTS EASTWARD
AND STRENGTHENS. THE INTENSITY IS ANTICIPATED TO DECREASE TO 55KTS
BY TAU 24 AS A RESULT OF SIGNIFICANT UPWELLING WHICH IS DECREASING
SSTS TO AS LOW AS 24C, DRY AIR ENTRAINMENT, AND MODERATE EASTERLY
WIND SHEAR (10-15KTS) PER JTWC SHIPS GUIDANCE. BETWEEN TAU 24-72
SHEAR IS EXPECTED TO DECREASE DRASTICALLY (1-5KTS) ALLOWING THE
STORM TO BECOME MORE VERTICALLY STACKED. COMBINED WITH A TRACK THAT
MOVES OUT OF THE AREA OF UPWELLING, AND INTO MORE FAVORABLE SSTS,
THE ANTICIPATED INTENSITY OF THE SYSTEM BY TAU 72 IS 80KTS. FOR THE
REMAINDER OF THE FORECAST PERIOD, WIND SHEAR IS ANTICIPATED TO
INCREASE, COMBINED WITH A SIGNIFICANT INFLUX OF MID-LEVEL DRY AIR,
WILL DECOUPLE THE VORTEX AND LEAD TO A SHARP DECREASE IN INTENSITY. 

MODEL DISCUSSION: DETERMINISTIC MODELS ARE IN GOOD AGREEMENT THAT
TC 06S (ANGGREK) WILL TRACK DUE WEST THROUGH TAU 12 WITH THE
EXCEPTION OF NAVGEM AND HAFS, WHICH EXPECT A SOUTHWESTWARD TRACK.
BY TAU 24, THERE IS ONLY A 40NM CROSS TRACK SPREAD AS THE STORM
MARKS THE TURN. THE LARGEST SPREAD OCCURS IN TRACK SPEED BETWEEN
TAU 72-120, OPENING FROM A 100NM SPREAD AT TAU 72 TO A 450NM SPREAD
AT TAU 120. GFS ANTICIPATES A FASTER TRACK TO SPEED COMPARED TO
MOST OTHER MEMBERS OF THE JTWC CONSENSUS. THE JTWC FORECAST IS
CONSISTENT WITH THE CONSENSUS MEAN TRACK BUT IS ABOUT TWO KNOTS
SLOWER THAN THE MEAN. THE INTENSITY MODEL GUIDANCE IS REFLECTED BY
THE DIFFERENCES IN TRACK GUIDANCE, AND DEPENDING ON HOW QUICKLY THE
STORM TRANSITS SOUTH HAS AN EQUAL WEIGHT IN HOW DRASTIC THE
INTENSITY IS EXPECTED TO INCREASE OR DECREASE. THE JTWC FORECAST
LIES BELOW THE CONSENSUS MEAN THROUGH THE BULK OF THE FORECAST
PERIOD, AS THE MEAN IS BEING PULLED TOO HIGH BY AN UNREALISTIC
SHIPS (NAVGEM VERSION) WHICH PEAKS THE INTENSITY AT AROUND 95 KNOTS.


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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