WDXS32 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.0S 88.3E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 980 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS DEEP
CONVECTIVE BANDING PERSISTING OVER THE CENTER OF A VERY COMPACT
CIRCULATION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON A DEFINED CENTER FEATURE EVIDENT IN A 271022Z SSMIS PASS.
THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON A CONSENSUS OF MULTI-AGENCY SUBJECTIVE DVORAK AND
AUTOMATED INTENSITY ESTIMATES LISTED BELOW. TC 06S HAS MAINTAINED
INTENSITY OVER THE PAST 12 HOURS WITH DEVELOPMENT CONSTRAINED BY
PERSISTENT, MODERATE EASTERLY VERTICAL WIND SHEAR, WHICH IS NOW
BEGINNING TO DECREASE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   DEMS: T3.5 - 55 KTS
   FMEE: T4.0 - 65 KTS
   FIMP: T3.5 - 55 KTS
   CIMSS SATCON: 51 KTS AT 270756Z
   CIMSS ADT: 55 KTS AT 271215Z
   CIMSS AIDT: 56 KTS AT 271245Z
   CIMSS D-MINT: 57 KTS AT 271022Z
   CIMSS D-PRINT: 56 KTS AT 271215Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 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: FORECASTED FORWARD TRACK SPEED IS
SLIGHTLY SLOWER IN THE 96 TO 120 HOUR PERIOD THAN REFLECTED IN THE
PREVIOUS WARNING. HOWEVER, THERE ARE NO SIGNIFICANT CHANGES TO THE
FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 09S IS EXPECTED TO CONTINUE TRACKING
WEST-SOUTHWESTWARD THROUGHOUT THE FORECAST PERIOD, STEERED THROUGH
TAU 72 BY THE SUBTROPICAL RIDGE TO THE SOUTH AND THEREAFTER BY A
SECOND RIDGE BUILDING TO THE SOUTHWEST OF THE SYSTEM. SLOW TO
STEADY INTENSIFICATION IS ANTICIPATED IN THE NEAR-TERM, SUPPORTED
BY DECREASING VERTICAL WIND SHEAR AND POLEWARD OUTFLOW ENHANCED BY
THE FLOW ASSOCIATED WITH AN UPPER-LEVEL TROUGH PASSING TO THE SOUTH
OF THE SYSTEM OVER THE NEXT 48 HOURS. MODEST WEAKENING IS
ANTICIPATED THEREAFTER AS EASTERLY VERTICAL WIND SHEAR AGAIN
INCREASES, THE OUTFLOW PATTERN BECOMES MORE RESTRICTED, AND THE
SYSTEM BEGINS TO ENTRAIN SLIGHTLY DRIER AIR. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK FORECAST GUIDANCE REMAINS
IN GOOD AGREEMENT WITH NO NOTABLE OUTLIERS. GIVEN TIGHT MODEL
AGREEMENT AND THE STRAIGHTFORWARD SYNOPTIC STEERING PATTERN, THE
JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS
WITH HIGH CONFIDENCE. CONSENSUS INTENSITY FORECAST MODELS ARE IN
GOOD AGREEMENT WITH THE OVERALL SCENARIO OF SLOW TO STEADY
NEAR-TERM INTENSIFICATION FOLLOWED BY WEAKENING LATE IN THE
FORECAST PERIOD. HAFS-A REMAINS A NOTEWORTHY OUTLIER, DEPICTING
RAPID INTENSIFICATION TO A PEAK OF 120 KNOTS BY TAU 48. THIS
SCENARIO CANNOT BE FULLY DISCOUNTED GIVEN VULNERABILITY OF THE
COMPACT SYSTEM TO SHIFTING ENVIRONMENTAL CONDITIONS, WHICH ARE
EXPECTED TO IMPROVE IMMINENTLY. THE CURRENT INTENSITY FORECAST
FAVORS THE MAJORITY OF THE GUIDANCE, CONSISTENT WITH PREVIOUS JTWC
FORECAST AND SLIGHTLY LOWER THAN THE CONSENSUS FORECAST THROUGH TAU
48.    

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