WDXS32 PGTW 281500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.1S 84.6E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 800 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 09S HAS STEADILY INTENSIFIED OVER THE PAST 12 HOURS UNDER THE
INFLUENCE OF SUPPORTIVE ENVIRONMENTAL CONDITIONS. ANIMATED ENHANCED
INFRARED (EIR) SATELLITE IMAGERY DEPICTS A PERSISTENT, SYMMETRICAL
SHIELD OF DEEP CONVECTION AND ASSOCIATED CIRRUS CLOUD COVER OVER A
LOW-LEVEL CIRCULATION CENTER EVIDENT IN RECENT MICROWAVE SATELLITE
IMAGERY INCLUDING A 281102Z GPM GMI PASS. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE GMI DATA AND SATELLITE
POSITION FIXES FORM PGTW, FMEE, FIMP, AND DEMS. THE INITIAL
INTENSITY OF 75 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 AND PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGING TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   FMEE: T5.0 - 90 KTS
   FIMP: T4.5 - 77 KTS
   CIMSS SATCON: 62 KTS AT 280738Z
   CIMSS ADT: 79 KTS AT 281200Z
   CIMSS AIDT: 67 KTS AT 281200Z
   CIMSS D-MINT: 70 KTS AT 281102Z
   CIMSS D-PRINT: 60 KTS AT 281230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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 09S WILL TRACK WEST-SOUTHWESTWARD TO
WESTWARD OVER THE NEXT 72 HOURS UNDER THE CONTINUED STEERING
INFLUENCE OF SUBTROPICAL RIDGING TO THE SOUTH. THEREAFTER, A SECOND
RIDGE BUILDING TO THE SOUTHWEST OF THE SYSTEM WILL TAKE OVER AS THE
PRIMARY STEERING MECHANISM, DEFLECTING TC 09S A BIT EQUATORWARD
DURING THE EXTENDED FORECAST PERIOD. FAVORABLY LOW VERTICAL WIND
SHEAR, SUFFICIENTLY WARM SEA SURFACE TEMPERATURES AND A NEAR-TERM
INCREASE IN POLEWARD OUTFLOW ENHANCED BY AN UPPER-LEVEL TROUGH
PASSING THE SOUTH ARE EXPECTED TO SUPPORT STEADY INTENSIFICATION
FOR THE NEXT 24 HOURS. THEREAFTER, UPPER-LEVEL OUTFLOW WILL BE
RESTRICTED AS THE TROUGH TO THE SOUTH TRANSLATES EASTWARD AND THE
COMPACT SYSTEM WILL CONTEND WITH THE HIGH LIKELIHOOD OF SLOW BUT
STEADY ENTRAINMENT OF DRIER AIR WRAPPING AROUND AND INTO THE SYSTEM
FROM THE SOUTH AND WEST, RESULTING IN A SLOW WEAKENING TREND.

MODEL DISCUSSION: NUMERICAL MODEL TRACK FORECAST GUIDANCE IS IN
VERY GOOD AGREEMENT THROUGH TAU 72 BUT DIVERGES SLIGHTLY IN
ORIENTATION DURING THE EXTENDED PERIOD DUE TO DIFFERING DEPICTIONS
OF THE SHIFT TO A NEW STEERING RIDGE TO THE SOUTHWEST OF THE
SYSTEM, WITH THE BRACKETING GFS AND ECMWF DETERMINISTIC MODEL
SOLUTIONS SEPARATED BY ABOUT 300 NM AT TAU 120. THE CURRENT JTWC
TRACK FORECAST IS CONSISTENT WITH THE PREVIOUS FORECAST AND
MULTI-MODEL CONSENSUS. INTENSITY FORECAST GUIDANCE SHOWS
SIGNIFICANT SPREAD IN THE NEAR-TERM, WITH HAFS-A DEPICTING RAPID
INTENSIFICATION TO A PEAK OF 115 KNOTS IN 24 HOURS ON THE HIGH END
AND COAMPS-TC AND GFS INDICATING A STEADY STATE OR MODEST
INTENSIFICATION TO ABOUT 80 KNOTS ON THE LOW END. ENVIRONMENTAL
CONDITIONS ARE ABOUT THE SAME AS THEY HAVE BEEN OVER THE PAST 12
HOURS, ASIDE FROM A SLIGHTLY IMPROVED POLEWARD OUTFLOW PATTERN, SO
THE CURRENT FORECAST ANTICIPATES A CONTINUATION OF THE RECENT SLOW
BUT STEADY TREND. HOWEVER, THE COMPACT SYSTEM IS SENSITIVE TO
SHIFTS IN ENVIRONMENTAL FACTORS AND A MORE RAPID INTENSIFICATION
RATE CANNOT BE RULED OUT.

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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