WDXS32 PGTW 250300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.9S 96.5E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 30 NM NORTHWEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT 
SYSTEM, WITH IMPROVED CONVECTIVE BANDING WRAPPING TIGHTLY INTO THE
LOW-LEVEL CIRCULATION CENTER (LLCC). A 242316Z SSMIS 37GHZ MICROWAVE 
IMAGE REVEALS A WELL-DEFINED LLCC, WHICH SUPPORTS THE INITIAL POSITION 
WITH HIGH CONFIDENCE. A 242300Z RCM-3 SAR IMAGE ALSO SUPPORTS THE 
INITIAL POSITION AND INDICATES A VMAX OF 47 KNOTS (MEAN), WITH A PEAK 
VALUE OF 54 KNOTS OVER THE SOUTHEAST QUADRANT. THE INITIAL INTENSITY OF 
45 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON SURFACE OBSERVATIONS 
FROM THE COCOS ISLANDS AND DVORAK ESTIMATES FROM PGTW AND DEMS. THE 
SYSTEM CENTER PASSED ABOUT 20-30NM NORTH OF THE COCOS ISLANDS AROUND 
242100-242300Z, WITH 10-MINUTE SUSTAINED WINDS PEAKING AT 42 KNOTS (45 
KNOTS CONVERTED TO 1-MINUTE AVERAGE), WITH MINIMUM SLP NEAR 997MB. 
ALTHOUGH MID-LEVEL DRY AIR HAS PERSISTED, THE COMPACT SYSTEM HAS 
DEVELOPED A SYMMETRIC MOIST CORE, WITH MODERATE POLEWARD OUTFLOW AND 
LOW VERTICAL WIND SHEAR (VWS), WHICH HAS ALLOWED THE SYSTEM TO SLOWLY
CONSOLIDATE OVER THE PAST 12 HOURS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: LOW-LEVEL SUBTROPICAL RIDGE (STR)
POSITIONED TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T2.5 - 35 KTS
   CIMSS SATCON: 37 KTS AT 242317Z
   CIMSS ADT: 37 KTS AT 242030Z
   CIMSS D-MINT: 32 KTS AT 242316Z
   CIMSS D-PRINT: 34 KTS AT 250030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 09S IS TRACKING SLOWLY
WESTWARD ALONG THE NORTHERN PERIPHERY OF A LOW-LEVEL (850MB) 
SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTH, WITH WEAKER RIDGING IN 
THE MID-LEVELS ASSOCIATED WITH A 500MB SHORTWAVE TROUGH PROPAGATING TO 
THE SOUTH. THE UPPER-LEVEL TROUGH IS EXPECTED TO TRACK QUICKLY EASTWARD 
OVER WESTERN AUSTRALIA ALLOWING THE STR TO STRENGTHEN TO THE SOUTH, 
ACCELERATING THE SYSTEM WESTWARD TO WEST-SOUTHWESTWARD THROUGH THE 
FORECAST PERIOD. TC 09S WILL CONTINUE TO INTENSIFY OVER THE NEXT 24 
HOURS TO ABOUT 60 KNOTS, WITH INCREASING VWS TILTING THE VORTEX AND DRY 
AIR ENTRAINMENT PRODUCING A STEADY WEAKENING TREND FROM TAU 24 THROUGH 
TAU 48. AFTER TAU 48, VWS IS FORECAST TO DECREASE, WITH IMPROVED 
POLEWARD VENTING LEADING TO A MORE FAVORABLE INTENSIFICATION PHASE AND
SECONDARY PEAK INTENSITY OF ABOUT 75 KNOTS BY TAU 120.    

MODEL DISCUSSION: DETERMINISTIC AND PROBABILISTIC TRACK GUIDANCE 
REMAINS IN TIGHT AGREEMENT THROUGH THE FORECAST PERIOD LENDING HIGH 
CONFIDENCE TO THE JTWC TRACK FORECAST. THE JTWC INTENSITY FORECAST, 
HOWEVER, IS ASSESSED WITH MEDIUM CONFIDENCE THROUGH TAU 72 DUE TO THE 
RAPIDLY EVOLVING ENVIRONMENT. IN THE LATER TAUS, RELIABLE INTENSITY 
GUIDANCE IS IN POOR AGREEMENT, WITH HAFS-A INDICATING A PEAK OF 135 
KNOTS AT TAU 120 AND COAMPS-TC (GFS BOUNDARY CONDITIONS) SHOWING A MUCH 
LOWER PEAK OF 80 KNOTS AT TAU 120. THE CURRENT FORECAST DOES NOT 
INDICATE AN RI PHASE DUE TO THE VERY LOW (20 PERCENT PROBABILITY AT TAU 
120) COAMPS-TC RI PROBABILITIES BUT WILL BE REASSESSED AS CONFIDENCE 
INCREASES.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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