WDXS32 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.7S 69.6E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 543 NM SOUTH-SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 23 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
LITTLE CHANGE HAS BEEN OBSERVED IN THE STRUCTURE OF TROPICAL
CYCLONE (TC) 09S (GRANT) OVER THE PAST TWELVE HOURS. THE SYSTEM
REMAINS COMPACT WITH DEEP CONVECTION SURROUNDING THE LOW-LEVEL
CIRCULATION CENTER AND CLOUD TOP TEMPERATURES HAVE WARMED ONLY
SLIGHTLY AS DEPICTED VIA ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY. TC GRANT CONTINUES TO TRACK WESTWARD INTO A DRIER
ENVIRONMENT AND INCREASED VERTICAL WIND SHEAR (20-25 KTS). THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON EIR
SATELLITE IMAGERY OF AN OBSCURED LLCC FEATURE. THE INITIAL
INTENSITY OF 100 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
OBJECTIVE AND SUBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   DEMS: T5.5 - 102 KTS
   CIMSS SATCON: 98 KTS AT 310300Z
   CIMSS ADT: 61 KTS AT 311230Z
   CIMSS AIDT: 68 KTS AT 311230Z
   CIMSS D-PRINT: 69 KTS AT 311230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE RADIAL

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 CONTINUE TO TRACK WESTWARD WITH
SLIGHTLY NORTHWESTWARD MOTION EXPECTED BETWEEN TAU 12 AND TAU 24. A
FORECASTED BUILDING OF THE SUBTROPICAL TO THE SOUTH WILL SUPPORT
THIS NORTHWESTWARD MOVEMENT SHIFT UNTIL STEERING INFLUENCE FROM THE
RIDGING OVER MADAGASCAR PUSHES THE SYSTEM SOUTHWESTWARD. A STEADY
WEAKENING TREND CAN BE EXPECTED AS THE CIRCULATION IS NOW
STRUGGLING AGAINST HIGHER VERTICAL WIND SHEAR, DRY AIR, AND A LESS
OPTIMAL OUTFLOW MECHANISM. THESE ENVIRONMENTAL CONDITIONS WILL
CONTINUE UNTIL AFTER TAU 96 WHEN A SLIGHT DROP IN VERTICAL WIND
SHEAR COULD ALLOW TC GRANT TO REGAIN SOME STRENGTH.

MODEL DISCUSSION: CROSS TRACK SPREAD AMONGST MODEL GUIDANCE SPREADS
ABOVE 100 NM PAST TAU 24 WITH THE MODELS STRUGGLING TO RESOLVE THE
STEERING INFLUENCE AND STRENGTH OF THE SUBTROPICAL RIDGE TO THE
SOUTH AND THE FORECASTED BUILDING OF THE RIDGE OVER MADAGASCAR. THE
JTWC FORECAST IS PLACED SLIGHTLY SOUTH OF THE MULTI MODEL CONSENSUS
WITH MEDIUM CONFIDENCE IN AN ATTEMPT TO SMOOTH OUT SOME OF THE MORE
NORTHERLY DEPICTIONS. INTENSITY GUIDANCE SPREADS UP TO 40 KTS AT
TAU 72. THE JTWC FORECASTED INTENSITY REFLECTS VALUES SLIGHTLY
BELOW THE MULTI MODEL CONSENSUS WITH MEDIUM CONFIDENCE INDICATING
SOME SKEPTICISM REGARDING FURTHER INTENSIFICATION AS ENVIRONMENTAL
CONDITIONS THAT ARE CURRENTLY WEAKENING THE SYSTEM (ESPECIALLY DRY
AIR AND VERTICAL WIND SHEAR) ARE NOT EXPECTED TO RELENT FOR LONG
ENOUGH FOR TC GRANT TO REGAIN MUCH STRENGTH. 

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