WDXS31 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (NINE)      
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.5S 66.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 617 NM EAST OF ST DENIS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
EXPOSED LOW-LEVEL CIRCULATION POSITIONED ON THE WESTERN EDGE OF AN
AREA OF ISOLATED, FLARING DEEP CONVECTION. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE EIR IMAGERY. A 312303Z
SSMIS 91 GHZ MICROWAVE IMAGE INDICATES WEAK OVERALL STRUCTURE WITH
NO DEFINED LOW-LEVEL CIRCULATION CENTER AND A LINEAR BAND OF
SHEARED DEEP CONVECTION OVER THE EASTERN QUADRANT. DESPITE THE
UNIMPRESSIVE CONVECTIVE STRUCTURE, A 311745Z ASCAT-C IMAGE SHOWED
30 TO 35 KNOTS OVER THE SOUTHERN SEMICIRCLE, WHICH SUPPORTS THE
INITIAL INTENSITY ASSESSMENT OF 35 KNOTS. AGENCY DVORAK ESTIMATES
ALSO SUPPORT THE INITIAL INTENSITY ASSESSMENT WITH HIGH CONFIDENCE.
ENVIRONMENTAL CONDITIONS REMAIN MARGINALLY FAVORABLE WITH MODERATE
TO HIGH VERTICAL WIND SHEAR (VWS) OFFSET SOMEWHAT BY MODERATE
POLEWARD VENTING.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A
SUBTROPICAL RIDGE (STR) POSITIONED TO THE WEST AND A WEAK STEERING
RIDGE TO THE EAST.    

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS ADT: 32 KTS AT 312100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: SYSTEM IS NOW EXPECTED TO UNDERGO
SUBTROPICAL TRANSITION VICE EXTRATROPICAL TRANSITION.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 09S IS FORECAST TO
REMAIN QUASI-STATIONARY THROUGH TAU 12 THEN GRADUALLY ACCELERATE
SOUTHEASTWARD AS THE STR STRENGTHENS TO THE EAST AND A HIGH
AMPLITUDE STEERING PATTERN SETS UP. THIS STEERING PATTERN WILL
DRIVE THE SYSTEM SOUTHEASTWARD THROUGH THE FORECAST PERIOD WITHIN
THE ENHANCED FLOW BETWEEN THE STR AND A DEEP UPPER-LEVEL TROUGH.
THE SYSTEM WILL INTERACT WITH A DEEP UPPER-LEVEL TROUGH AFTER TAU
36 AND COMMENCE SUBTROPICAL TRANSITION AS IT TRACKS UNDER A
SUBTROPICAL JET. VWS WILL INCREASE TO 35 TO 45 KNOTS WITH DRY AIR
ENVELOPING THE SYSTEM AFTER TAU 48. SOME INTENSIFICATION IS LIKELY
BUT IS ASSOCIATED WITH THE AFOREMENTIONED DEEP UPPER-LEVEL TROUGH
AS THE SYSTEM COMPLETES SUBTROPICAL TRANSITION. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
LENDING MEDIUM OVERALL CONFIDENCE IN THE JTWC TRACK FORECAST. THERE
IS MEDIUM CONFIDENCE IN THE JTWC INTENSITY FORECAST, WITH GUIDANCE
INDICATING A PEAK INTENSITY IN THE 40 TO 60 KNOT RANGE. HAFS-A
PEAKS THE INTENSITY AT 53 KNOTS AT TAU 72 WHILE COAMPS-TC (NAVGEM)
PEAKS THE INTENSITY AT 60 KNOTS AT TAU 72. HAFS-A AND COAMPS-TC
(NAVGEM) ARE ASSESSED AS UNREALISTIC DUE TO THE UNFAVORABLE
ENVIRONMENT AFTER TAU 36.   

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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