WDXS31 PGTW 162100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (THIRTEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.1S 68.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 485 NM SOUTH-SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING SYSTEM UNDER SHEAR FROM THE EAST WITH SUSTAINED,
FLARING CONVECTION OVER THE CENTER. THE INITIAL POSITION IS BASED
OFF A 161720Z PARTIAL ASCAT-C IMAGE DEPICTING HALF OF A CIRCULATION
WITH 25 KT WINDS ABOUT 20 NM FROM THE CENTER OF THE CIRCULATION IN
THE NORTHEAST QUADRANT. THE INITIAL INTENSITY OF 35 KTS IS HEDGED
SLIGHTLY HIGHER THAN THE PGTW DVORAK CURRENT INTENSITY ESTIMATE OF
2.0 (30 KTS) BUT IS IN LINE WITH FMEE AT 2.5 (35 KTS). TC 13S IS
CURRENTLY IN A MARGINALLY FAVORABLE ENVIRONMENT DUE TO MODERATE
VERTICAL WIND SHEAR OF 20-25 KTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   FMEE: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TC 13S IS FORECAST TO CONTINUE GENERALLY
WESTWARD UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE TO THE SOUTH
OVER THE NEXT 24 HOURS WITH MODERATE INTENSIFICATION. AFTER TAU 24,
THE SYSTEM WILL HAVE REACHED 55 KTS AND BEGIN TO TURN SOUTHWESTWARD
AS THE RIDGE IS DEGRADED BY A PASSING MIDLATITUDE TROUGH. IT WILL
CONTINUE THIS DIRECTION, REACHING AN INTENSIFICATION OF 95 KTS BY
TAU 96. AROUND THIS TIME, TC 13S WILL TURN SLIGHTLY WEST-SOUTHWESTWARD 
AS ANOTHER SUBTROPICAL RIDGE BUILDS TO THE SOUTH. THE SYSTEM IS 
EXPECTED TO BE UNDER MODERATE VERTICAL WIND SHEAR FOR MOST OF THE 
FORECAST THUS LIMITING PEAK INTENSIFICATION TO AROUND 95 KTS BY TAU 
120.

MODEL DISCUSSION: NUMERICAL MODELS ARE CURRENTLY IN GOOD AGREEMENT
IN REGARDS TO TRACK FORECAST WITH ONLY A 110 NM CROSS-TRACK SPREAD
AT TAU 120. THIS EXCLUDES NVGM AS AN OUTLIER WHICH TRACKS THE
SYSTEM ABOUT 250 NM SOUTH OF CONSENSUS. INTENSITY GUIDANCE IS ALSO
IN FAIRLY GOOD AGREEMENT WITH MOST MODELS SHOWING A PERIOD OF
MODERATE INTENSIFICATION UP TO TAU 96. HOWEVER, THERE IS SOME
SPREAD IN PEAK INTENSITY. FOR EXAMPLE, HWRF PEAKS AT 85 AND GFS
PEAKS AT 95 KTS. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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