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

SUMMARY:
   INITIAL POSITION: 14.2S 67.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 508 NM SOUTH-SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAPIDLY
CONSOLIDATING SYSTEM ATTEMPTING TO FORM AN EYE. THE INITIAL POSITION 
IS BASED OFF A 162304Z SSMIS 91GHZ IMAGE SHOWING LOW LEVEL BANDING 
PARTIALLY OBSCURED BY WHAT APPEARS TO BE A CENTRAL DENSE OVERCAST OF 
CONVECTION. THE INITIAL INTENSITY OF 45 KTS IS BASED OFF THE PGTW 
DVORAK CURRENT INTENSITY ESTIMATE OF 3.0 (45 KTS) AND ADT AT 47 KTS. 
TC 13S IS CURRENTLY IN A FAVORABLE ENVIRONMENT AND IS CURRENTLY 
UNDERGOING RAPID INTENSIFICATION DESPITE MODERATE VERTICAL WIND 
SHEAR OF 20-25 KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS SATCON: 48 KTS AT 162057Z
   CIMSS ADT: 47 KTS AT 170015Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 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: THE SHORT-TERM INTENSITY FORECAST HAS
BEEN INCREASED DUE TO THE ONSET OF RAPID INTENSIFICATION.

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 RAPID INTENSIFICATION. AFTER TAU
24, THE SYSTEM WILL BEGIN TO TURN SOUTHWESTWARD AS THE RIDGE IS 
DEGRADED BY A PASSING MIDLATITUDE TROUGH. IT WILL CONTINUE THIS 
DIRECTION, REACHING A PEAK INTENSIFICATION OF 100 KTS BY
TAU 72. AFTERWARDS, TC 13S WILL TURN SLIGHTLY WEST-SOUTHWESTWARD AS 
ANOTHER SUBTROPICAL RIDGE BUILDS TO THE SOUTH. THE SYSTEM WILL BEGIN 
TO DECREASE IN INTENSITY BY TAU 96 AS IT ENTERS INTO A WAKE OF LOWER 
OCEAN HEAT CONTENT LEFT BY TC 08S.

MODEL DISCUSSION: NUMERICAL MODELS ARE CURRENTLY IN GOOD AGREEMENT
IN REGARDS TO TRACK FORECAST WITH ONLY A 100 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. HOWEVER, RIPA HAS BEEN TRIGGERED, WHICH LENDS 
CONFIDENCE TO THE RAPID INTENSIFICATION FORECAST.

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

4.JUSTIFICATION FOR AMENDMENT: AMENDED FORECASTED INTENSITY DUE TO 
RAPID INTENSIFICATION.//
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