WDXS32 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
030//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.2S 69.1E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 581 NM SOUTH-SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 09S (GRANT) WITH A DETERIORATING STRUCTURE AS THE
CONVECTION IS HEAVILY SHEARED TO THE WEST. A 312158Z GMI 37 GHZ
MICROWAVE IMAGE SHOWED THAT THE MICROWAVE EYE FEATURE IS NOW
DISPLACED TO THE EAST OF THE DEEP CONVECTION, SHOWING SIGNIFICANT
VORTEX TILT WITH HEIGHT. ENVIRONMENTAL ANALYSIS INDICATES THAT 09S
IS IN A MARGINAL ENVIRONMENT CHARACTERIZED BY MODERATE OUTFLOW,
MODERATE TO HIGH (20-25 KTS) EASTERLY VERTICAL WIND SHEAR, DRY AIR
ENTRAINMENT, AND WARM (27-28 C) SEA SURFACE TEMPERATURES. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
ANIMATED EIR IMAGERY AND EXTRAPOLATION FROM THE AFOREMENTIONED GMI
MICROWAVE IMAGE. THE INITIAL INTENSITY OF 70 KTS IS ASSESSED WITH
LOW CONFIDENCE BASED ON THE LARGE SPREAD BETWEEN THE OBJECTIVE
CIMSS ESTIMATES AND AGENCY DVORAK FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   DEMS: T5.0 - 90 KTS
   FMEE: T4.5 - 77 KTS
   FIMP: T5.0 - 90 KTS
   CIMSS ADT: 82 KTS AT 312200Z
   CIMSS AIDT: 79 KTS AT 312200Z
   CIMSS D-MINT: 59 KTS AT 312201Z
   CIMSS D-PRINT: 55 KTS AT 312200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: SLIGHT DRY AIR ENTRAINMENT FROM THE NORTH

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 IS FORECAST TO TRACK SLOWLY EASTWARD
THROUGH TAU 12 AS IT BEGINS TO SEPARATE FROM THE STR TO THE
SOUTHEAST. NEAR TAU 24, A SECOND STR IS EXPECTED TO BUILD TO THE
SOUTH OF THE SYSTEM, CAUSING IT TO TRACK GENERALLY WESTWARD THROUGH
TAU 72.  AFTER TAU 72, 09S WILL BEGIN TO ROUND THE NORTHWESTERN
EXTENT OF THAT STR, INITIATING A SOUTHWESTWARD TURN. 09S IS THEN
FORECAST TO CONTINUE ON A SOUTHWESTWARD TRAJECTORY THROUGH THE
REMAINDER OF THE FORECAST PERIOD. REGARDING INTENSITY, 09S IS
FORECAST TO CONTINUE WEAKENING THROUGH TAU 36 AS SHEAR REMAINS
MODERATE TO HIGH AND DRY AIR CONTINUES TO IMPACT THE VORTEX. NEAR
TAU 72, SHEAR AND DRY AIR ARE EXPECTED TO IMPROVE, ALLOWING FOR 09S
TO REINTENSIFY THROUGH TAU 120. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGHOUT THE FORECAST PERIOD, WITH THE EXCEPTION OF
NAVGEM. GALWEM MAKES UP THE SOUTHERNMOST MEMBER WHILE THE ECMWF
ENSEMBLE MEAN MAKES UP THE NORTHERNMOST MEMBER. THE JTWC TRACK
FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS (AFTER
THROWING OUT NAVGEM) WITH MEDIUM CONFIDENCE. ALL MODELS AGREE ON
WEAKENING THROUGH TAU 60. HOWEVER, AFTER TAU 60 SOME MODELS
EXTREMELY RAPIDLY STRENGTHEN THE SYSTEM. HWRF AND COAMPS-TC ARE THE
STRONGEST MODELS, SUGGESTING OVER 100 KTS AT TAU 120. THE JTWC
INTENSITY FORECAST IS MORE IN LINE WITH HAFS-A AFTER TAU
72. OVERALL, THERE IS MEDIUM CONFIDENCE IN THE JTWC INTENSITY
FORECAST THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER. 

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