WDXS32 PGTW 172100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 06S (ANGGREK) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.6S 94.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 1295 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 06S (ANGGREK) HAS A PARTIALLY OBSCURED LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH CONTINUOUS CONVECTIVE ACTIVITY
WRAPPING CYCLONICALLY AROUND THE EASTERN PERIPHERY OF THE SYSTEM.
OVERALL VERTICAL TILT OF TC 06S HAS DECREASED OVER THE LAST SIX
HOURS, AS FLARING CONVECTION AROUND THE CIRCULATION CENTER IS
ATTEMPTING TO WRAP INTO THE EASTERN SEMICIRCLE. THE INITIAL
POSITION WAS IDENTIFIED WITH MEDIUM CONFIDENCE BY HIMAWARI-9
ANIMATED VISIBLE AND INFRARED IMAGERY AND A PARTIAL 171556Z ASCAT
PASS, REVEALING MOVEMENT OF TC 05S TO THE SOUTH FROM SIX HOURS AGO,
WITH WEAK WESTWARD OUTFLOW ALOFT ASSOCIATED WITH AN AREA OF WEAK
UPPER-LEVEL DIFFLUENCE. THE INITIAL INTENSITY WAS ASSESSED WITH
MEDIUM CONFIDENCE WITH THE AFOREMENTIONED ASCAT PASS, AND REAL-TIME
CIMMS SUMMARIES SHOW INTENSITIES IN CLOSE PROXIMITY TO THE LLCC
RANGING BETWEEN 35-45 KNOTS. 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
CONTINUES TO BE THE DENSE SWATH OF DRY AIR ENCOMPASSING THE
SOUTHERN HALF OF TC 06S.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 43 KTS AT 171449Z
   CIMSS ADT: 41 KTS AT 171730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 27-29 CELSIUS
   OUTFLOW: WEAK WESTWARD

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: TC 06S (ANGGREK) IS FORECASTED TO CONTINUE
TRACKING SOUTH THROUGH TAU 24, SKIRTING THE EDGE OF THE
WELL-ESTABLISHED RIDGE TO THE EAST. AS THE SUBTROPICAL RIDGE (STR)
CONTINUES TO BUILD TO THE EAST, THE STEERING MECHANISM WILL
PROGRESS THE SYSTEM GENERALLY TO THE SOUTHWEST INTO TAU 48 AND
EVENTUALLY PROGRESS WESTWARD AT TAU 72 AND THROUGH THE REMAINDER OF
THE FORECAST PERIOD. SYSTEM INTENSITY IS EXPECTED TO CONTINUE TO
STEADILY INCREASE THROUGH TAU 36 DUE TO MARGINALLY FAVORABLE
ENVIRONMENTAL CONDITIONS, INCLUDING WARM SSTS (27-29C), RELATIVELY
LOW VERTICAL WIND SHEAR (VWS), AND WESTWARD UPPER-LEVEL OUTFLOW.
THE PRIMARY LIMITING FACTOR IN PREVENTING CONTINUED INTENSIFICATION
PAST TAU 36 IS THE LARGE SWATH OF DRY AIR EXTENDING AROUND THE 
ENTIRETY OF THE SOUTHERN HALF OF TC 06S. BY TAU 60, DRY AIR WILL 
COMPLETELY WRAP THE SYSTEM FROM THE WEST AND CONTINUE THROUGH TAU 120.
MID-LEVEL VWS IS ANTICIPATED TO CONTINUE BETWEEN 15-20 KTS THROUGH
THE REMAINDER OF THE PERIOD, BUT WILL ULTIMATELY BE OFFSET BY THE
FAVORABLE ENVIRONMENTAL CONDITIONS MENTIONED ABOVE, SLIGHTLY
INTENSIFYING TO A FORECASTED 60 KTS BY TAU 24-48. NEAR THE END OF
THE FORECAST, THE DRY AIR ENTRAINMENT AND INCREASED INFLUENCE FROM
THE MID-LEVEL VWS WILL LEAVE TO A SLOW AND STEADY WEAKENING BY TAU
120. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN RELATIVELY
GOOD AGREEMENT THAT TC 06S (ANGGREK) WILL CONTINUE TO THE
SOUTH-SOUTHWEST THROUGH TAU 48, AND BEGIN TO VEER WESTWARD SHORTLY
THEREAFTER THROUGH THE REMAINDER OF THE FORECAST PERIOD, BEING
HEAVILY INFLUENCED BY THE STEERING RIDGE TO THE SOUTH. AT TAU 24,
THE JTWC CONSENSUS MEMBERS CROSS-TRACK SPREAD REMAINS AT 35NM, ALL
HEADING TO THE SOUTH-SOUTHWEST. BY TAU 48, CROSS-TRACK SPREAD
INCREASES TO 50NM AS TC 06S BEGINS ITS TREK WESTWARD WITH THE
INFLUENCE OF ITS PRIMARY STEERING MECHANISM. BY TAU 72, ALL MEMBERS
SHOW A SIMILAR WESTWARD PROGRESSION, ALTHOUGH MOVEMENT SPEED
VARIES. THE PRIMARY FACTOR BETWEEN STEERING AND STORM MOVEMENT
SPEED IS DUE TO THE STRENGTH OF THE STEERING RIDGE TO THE SOUTH.
CONSENSUS MEMBERS AGREE THAT STORM INTENSITY WILL REMAIN TO
INTENSIFY TO 60 KTS BETWEEN TAU 36-48, AND STEADILY DECREASE TO 50
KTS SHORTLY THEREAFTER UNTIL THE END OF THE FORECAST PERIOD. 

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