WDXS32 PGTW 160900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 06S (ANGGREK) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.4S 93.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 247 NM NORTHWEST OF COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 06S (ANGGREK) STAGNATING IN A QUASI-STATIONARY POSITION 
AS IT HAS HAD LITTLE FORWARD MOMENTUM OVER THE LAST 12 HOURS. DEEP
LAYER CONVECTION PERSISTS BUT IS CONFINED TO THE WESTERN SEMICIRCLE
DUE TO THE INFLUENCE OF PERSISTENT EASTERLY SHEAR VECTOR.
EQUATORWARD OUTFLOW ALOFT IS EVIDENT WITH CIRRUS SHIELDING
EXPANDING TO THE NORTHWEST. DESPITE LOW DEEP LEVEL SHEAR, ESTIMATED
BY CIMSS AT 5 KTS, MID-LEVEL SHEAR IS APPROXIMATELY 25KTS BASED ON
GFS MODEL SOUNDINGS. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE BASED ON ANIMATED MSI AND HIGH-RESOLUTION VISIBLE
IMAGERY DUE TO A LACK OF RECENT MICROWAVE IMAGERY. THE INITIAL
INTENSITY IS BASED ON A 160244Z ASCAT-B PASS SHOWING WIND SPEEDS OF
AROUND 40 KTS, SLIGHTLY LOWER THAN THE AGENCY FIXES THAT ARE ALL AT
T3.0, AND IN LINE WITH THE 40KT SATCON ESTIMATE. ENVIRONMENTAL
ANALYSIS REVEALS A FAVORABLE ENVIRONMENT WITH LOW DEEP LAYER
SHEAR, WITH THE NOTED HIGHER MID-LEVEL SHEAR, MODERATE POLEWARD AND
EQUATORWARD OUTFLOW AND WARM SEA SURFACE TEMPERATURES (28 C). THE
SYSTEM IS TO THE SOUTH OF THE NEAR EQUATORIAL RIDGE (NER), BUT
NORTH OF A SUBTROPICAL RIDGE (STR), WITH A RESULTING WEAK STEERING
ENVIRONMENT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN WITH NER TO THE
NORTH AND A SUBTROPICAL RIDGE (STR) TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 40 KTS AT 160630Z
   CIMSS ADT: 35 KTS AT 160530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS FORECAST INTRODUCES A
DISSIPATION BY THE END OF THE FORECAST PERIOD.

FORECAST DISCUSSION: WHILE CURRENTLY QUASI-STATIONARY, TC 06S WILL
BEGIN TO MOVE OUT SLOWLY TO THE EAST-SOUTHEAST SHORTLY AS THE
GRADIENT WITH THE NER STRENGTHENS, WITH TRACK SPEEDS EXPECTED TO
REMAIN BELOW 3 KNOTS FOR THE NEXT 24 HOURS. BY TAU 48, THE NER WILL
FORM A NORTH-SOUTH RIDGE COMPLEX EAST OF THE SYSTEM, EXTENDING FROM
BORNEO TO THE WEST OF LEARMONTH, AUSTRALIA, FORCING TC 06S TO
TRAVEL SOUTH-SOUTHWEST THROUGH TAU 72. A COMPETING STEERING
ENVIRONMENT SETS UP AFTER TAU 72 AS THE NER PUSHES SOUTH TO NEAR
SINGAPORE, WHILE A STR DEVELOPS TO THE SOUTH OF THE TC, GENERATING
ANOTHER WEAK STEERING PATTERN. THIS WILL CAUSE THE SYSTEM TO SLOW
DOWN TO A CRAWL, OR BECOME QUASI-STATIONARY, THROUGH THE REMAINDER
OF THE FORECAST PERIOD. AS THE STORM MOVES SOUTHWARD, IT MOVES INTO
A SLIGHTLY MORE FAVORABLE ENVIRONMENT WITH THE MID-LEVEL SHEAR
DECREASING SLIGHTLY AND IMPROVES UPPER-LEVEL OUTFLOW WHICH WILL
ALLOW FOR A BRIEF PERIOD OF INTENSIFICATION THROUGH TAU 36. AFTER
TAU 48, THE MID-LEVEL SHEAR (20-25KTS), REDUCED OUTFLOW, AND DRY AIR
ENTRAINMENT WILL CHOKE THE SYSTEM, CAUSING A SLOW BUT STEADY DROP
IN INTENSITY, WITH THE SYSTEM ULTIMATELY ANTICIPATED TO DISSIPATE
BY TAU 120.

MODEL DISCUSSION: GLOBAL NUMERICAL MODEL GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 72 THAT THE SYSTEM WILL VEER EAST-SOUTHEAST
AND THEN TO THE SOUTH-SOUTHWEST. CROSS-TRACK SPREAD GRADUALLY
INCREASES TO 175 MILES BY TAU 72, WITH NAVGEM MARKING THE WESTERN
SIDE AND UKMET ENSEMBLE MARKING THE EAST SIDE OF THE GUIDANCE. THE
JTWC TRACK IS CONSISTENT WITH THE GFS AND CONSENSUS MEAN WITH
MEDIUM CONFIDENCE. BEYOND TAU 72, THE MODEL GUIDANCE SPLITS 180
DEGREES WITH A 500 MILE SPREAD BETWEEN NAVGEM TO THE FAR WEST AND
UKMET ENSEMBLE TO THE FAR EAST, RESULTING IN SIGNIFICANT
UNCERTAINTY IN THE TRACK FORECAST THROUGH TAU 120. THE ECENS AND
GEFS ALSO SHOW A 180 DEGREE SPLIT WITH ROUGHLY HALF OF THE MEMBERS
GOING WEST AND HALF GOING EAST, HIGHLIGHTING THE EXTREME
UNCERTAINTY IN THE FORECAST, PARTICULARLY AFTER TAU 72. THE
INTENSITY GUIDANCE ACROSS THE MODELS IS IN GOOD AGREEMENT
THROUGHOUT THE FORECAST PERIOD, PARTICULARLY PEAKING BY TAU 36 AND
REPRESENTING A STEADY DECLINE THROUGH TAU 120. 

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