WDXS32 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.8S 90.1E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 400 NM WEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 09S (GRANT) WITH PERSISTENT DEEP CONVECTION SLIGHTLY OFFSET
TO THE WEST OF A HIGHLY COMPACT LOW-LEVEL CIRCULATION CENTER
(LLCC). WITHIN THE STRONGEST CONVECTIVE BURSTS, THE CLOUD TOPS ARE
MEASURING COLDER THAN -85 C. A 262353Z WSFM 37 GHZ MICROWAVE IMAGE
REVEALED A WELL-DEFINED MICROWAVE EYE FEATURE, LENDING HIGH
CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY OF 60 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES
AND CIMSS OBJECTIVE ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS
INDICATES THAT 09S IS IN A MARGINALLY FAVORABLE ENVIRONMENT
CHARACTERIZED BY MODERATE POLEWARD OUTFLOW ALOFT, MODERATE (15-20
KTS) EASTERLY VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA SURFACE
TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   DEMS: T3.5 - 55 KTS
   APRF: T3.5 - 55 KTS
   CIMSS ADT: 55 KTS AT 270015Z
   CIMSS AIDT: 56 KTS AT 270015Z
   CIMSS D-MINT: 51 KTS AT 270019Z
   CIMSS D-PRINT: 55 KTS AT 262345Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 09S IS FORECAST TO TRACK
WEST-SOUTHWESTWARD, ALONG THE NORTHERN PERIPHERY OF THE STR TO THE
SOUTH THROUGH TAU 72. NEAR TAU 72, A SECOND STR IS EXPECTED TO
BUILD TO THE SOUTH OF THE SYSTEM, CAUSING 09S TO CONTINUE ON A
WEST-SOUTHWESTWARD TRAJECTORY THROUGH THE REMAINDER OF THE FORECAST
PERIOD. REGARDING INTENSITY, 09S IS FORECAST TO MAINTAIN INTENSITY
OVER THE NEXT 24 HOURS AS EASTERLY SHEAR CONTINUES TO IMPACT THE
VORTEX. AROUND TAU 24, THE SHEAR IS EXPECTED TO BEGIN
DECREASING, ALLOWING FOR THE VORTEX TO BECOME MORE VERTICALLY
ALIGNED. AS A RESULT, 09S IS FORECAST TO INTENSIFY FROM TAU 24 TO
TAU 72, UP TO A PEAK OF AROUND 80 KTS. EASTERLY SHEAR IS THEN
FORECAST TO INCREASE AFTER TAU 72, CAUSING THE INTENSIFICATION
TREND TO COME TO A HALT. ADDITIONALLY, DRY AIR WILL BEGIN TO ENTRAIN 
INTO THE SYSTEM FROM THE NORTH. THESE TWO FACTORS WILL CAUSE 09S TO 
WEAKEN FROM TAU 96 THROUGH THE END OF THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH NO NOTABLE OUTLIERS. CROSS-TRACK SPREAD AT TAU 72 IS
90 NM WHICH OPENS UP TO 150 NM AT TAU 120. ALONG-TRACK SPREAD DOES
INCREASE TO AROUND 200 NM AT TAU 120 THOUGH. THE JTWC TRACK
FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH
CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER.
INTENSITY GUIDANCE HAS ONE SIGNIFICANT OUTLIER IN HAFS-A. IT
SUGGESTS A PEAK INTENSITY OF OVER 125 KTS AT TAU 60, WHICH IS
CONSIDERABLY HIGHER THAN THE REMAINDER OF GUIDANCE. THE REST OF THE
INTENSITY GUIDANCE FALLS WITHIN THE 60-80 KNOT RANGE FOR THE PEAK.
THE JTWC INTENSITY FORECAST IS PLACED NEAR THE CONSENSUS WITH
OVERALL MEDIUM CONFIDENCE. 

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