WDXS32 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.7S 80.5E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 616 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 09S HAS CONTINUED TO RAPIDLY INTENSIFY OVER THE PAST 12 HOURS.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
PERSISTENT DEEP CONVECTIVE BANDING SURROUNDING AN APPROXIMATELY 12
NM DIAMETER EYE. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON A 291130Z PGTW SATELLITE EYE FIX AND SSMIS
IMAGERY FROM 291237Z. THE INITIAL INTENSITY OF 120 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON A CONSENSUS OF SUBJECTIVE DVORAK
AND AUTOMATED INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   DEMS: T6.0 - 115 KTS
   FMEE: T6.0 - 115 KTS
   FIMP: T6.0 - 115 KTS
   CIMSS SATCON: 108 KTS AT 291237Z
   CIMSS ADT: 122 KTS AT 291200Z
   CIMSS AIDT: 123 KTS AT 291200Z
   CIMSS D-MINT: 103 KTS AT 291237Z
   CIMSS D-PRINT: 116 KTS AT 291300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 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 WILL TRACK WESTWARD TO
WEST-SOUTHWESTWARD OVER THE NEXT 48 HOURS UNDER THE CONTINUED
STEERING INFLUENCE OF THE STR TO THE SOUTH. A SECOND STR BUILDING
TO THE SOUTHWEST OF THE SYSTEM WILL BECOME THE DOMINANT STEERING
MECHANISM BY TAU 72 AND DEFLECT THE SYSTEM WEST-NORTHWESTWARD FOR
THE REMAINDER OF THE FORECAST PERIOD. ALTHOUGH ENVIRONMENTAL
CONDITIONS WILL REMAIN GENERALLY FAVORABLE IN THE NEAR-TERM,
RECENTLY OBSERVED ROBUST POLEWARD OUTFLOW IS EXPECTED TO BEGIN
DECREASING AND THE SYSTEM SHOULD RESPOND WITH SLOW WEAKENING. BY
TAU 36, VERTICAL WIND SHEAR IS EXPECTED TO INCREASE AND THE SYSTEM
WILL BEGIN TO ENTRAIN DRIER AIR FROM THE SURROUNDING ENVIRONMENT.
COUPLED WILL PASSAGE OVER SLIGHTLY COOLER WATER, THE SYSTEM IS
EXPECTED TO GRADUALLY WEAKEN FOR THE REMAINDER OF THE FORECAST
PERIOD. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK FORECAST GUIDANCE IS IN
VERY GOOD AGREEMENT THROUGH TAU 48 AND BEGINS TO SPREAD THEREAFTER
AS THE PRIMARY STEERING MECHANISM SHIFTS TO A BUILDING STR TO THE
SOUTHWEST. MODEL SOLUTIONS FAN RATHER EVENLY AROUND THE CONSENSUS
MEAN TRACK IN THE EXTENDED PERIOD, SO THE CURRENT JTWC FORECAST
FAVORS THE CONSENSUS TRACK AND IS CONSISTENT WITH THE PREVIOUS
FORECAST. MODEL INTENSITY FORECASTS AGREE ON A STEADY WEAKENING
TREND THROUGH TAU 120 WITH THE EXCEPTION OF COAMPS-TC, WHICH
DEPICTS POTENTIAL RE-INTENSIFICATION AFTER TAU 72. IN CONTRAST,
HAFS-A AND GFS DEPICT EVEN SHARPER WEAKENING THAN REFLECTED IN THE
CURRENT FORECAST BASED ON A STRONGER ANTICIPATED RESPONSE TO
DECREASING OUTFLOW, INCREASING SHEAR, AND ENTRAINMENT OF DRIER AIR.
THE CURRENT FORECAST HOLDS THE MIDDLE GROUND FOR NOW AND IS
CONSISTENT WITH THE PREVIOUS JTWC INTENSITY FORECAST.

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