WDXS32 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.5S 82.5E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 704 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 09S (GRANT) WITH AN 8 NM PINHOLE EYE AND VERY COLD (-75 C)
CLOUD TOPS ENTIRELY ENCIRCLING THE EYE. 09S IS ANALYZED TO HAVE
RAPIDLY INTENSIFIED FROM 75 KTS 24 HOURS AGO TO 105 KTS NOW.
HOWEVER, THE STRUCTURE HAS STARTED TO SLIGHTLY DEGRADE FROM 0000Z
TO 0200Z. THE INTENSITY OF 09S IS LIKELY TO FLUCTUATE AS THE SMALL
SIZE OF THE SYSTEM MAKES IT MORE SUSCEPTIBLE TO THE ENVIRONMENT.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
PINHOLE EYE IN ANIMATED EIR IMAGERY. THE INITIAL INTENSITY OF 105
KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK
AND CIMSS OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL
ANALYSIS INDICATES THAT 09S IS IN A HIGHLY FAVORABLE ENVIRONMENT
CHARACTERIZED BY STRONG POLEWARD OUTFLOW, LOW (5-10 KTS) VERTICAL
WIND SHEAR, AND WARM (27-28 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: PERSISTENCE WITH SLIGHT ADJUSTMENTS BASED
ON THE OBJECTIVE BEST TRACK

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   DEMS: T5.5 - 102 KTS
   FMEE: T6.0 - 115 KTS
   FIMP: T5.5 - 102 KTS
   CIMSS ADT: 99 KTS AT 290000Z
   CIMSS AIDT: 101 KTS AT 290000Z
   CIMSS D-MINT: 108 KTS AT 290001Z
   CIMSS D-PRINT: 100 KTS AT 290000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE NEAR-TERM INTENSITY IS FORECAST
TO BE HIGHER THAN PREVIOUSLY FORECAST DUE TO THE RAPID
INTENSIFICATION AND FORMATION OF A PINHOLE EYE.

FORECAST DISCUSSION: 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 SOUTHWEST
OF THE SYSTEM, CAUSING 09S TO TAKE A BRIEF WEST-NORTHWESTWARD TURN.
REGARDING INTENSITY, 09S IS FORECAST TO PEAK NEAR TAU 12, THOUGH
RECENT IMAGERY SUGGESTS THE PEAK MAY HAVE ALREADY OCCURRED.
NONETHELESS, THE ENVIRONMENT WILL REMAIN FAVORABLE THROUGH TAU 24
WITH STRONG POLEWARD OUTFLOW AND LOW VERTICAL WIND SHEAR. AFTER TAU
24, NORTHEASTERLY SHEAR IS EXPECTED TO INCREASE, CAUSING 09S TO
BEGIN WEAKENING. AROUND TAU 72, DRY AIR IS ALSO EXPECTED TO BEGIN
ENTRAINING INTO THE VORTEX FROM THE NORTH, FURTHER WEAKENING THE
SYSTEM. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT THROUGH TAU 72 WITH A 75 NM CROSS-TRACK SPREAD AT TAU 72.
AFTER TAU 72, MODELS SLIGHTLY DIVERGE DUE TO DIFFERENCES IN
FORMATION AND INTERACTION WITH THE SECOND STR. CROSS-TRACK SPREAD
INCREASES TO AROUND 250 AT TAU 120. THE JTWC TRACK FORECAST IS
PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE
THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER. MESOSCALE MODELS
RANGE FROM SLIGHT WEAKENING THROUGH TAU 12 (HWRF) TO SLIGHT
INTENSIFICATION (HAFS-A). AFTER TAU 12, MODELS GENERALLY AGREE ON
WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE JTWC
INTENSITY FORECAST FOLLOWS CLOSELY TO THE HAFS-A 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//
NNNN