WDXS32 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DINGANI) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.3S 86.3E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 980 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT CIRCULATION, WHICH HAS BECOME FULLY EXPOSED, AFTER HAVING
BEEN PARTIALLY OBSCURED OVER THE PREVIOUS 12 HOURS. THE LOW-LEVEL
CIRCULATION CENTER (LLCC) IS EMBEDDED WITHIN A LARGER REGION OF
CYCLONIC ROTATION, OUTLINED BY AREAS OF FLARING CONVECTION,
PARTICULARLY ON THE SOUTHWESTERN PERIPHERY. A 091531Z ASCAT-C PASS
REVEALED A COMPACT CIRCULATION NEAR OR JUST EAST OF THE EASTERN
EDGE OF DEEP CONVECTION. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE EXPOSED CIRCULATION ALONG WITH THE ASCAT
PASS. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE AS WELL
BASED ON THE ASCAT-C WHICH SHOWS A SWATH OF 35-40 KNOT WINDS IN THE
SOUTHWESTERN QUADRANT. THE ENVIRONMENTAL CONDITIONS ARE MARGINALLY
FAVORABLE FOR DEVELOPMENT, WITH WARM (26-27C) SEA SURFACE
TEMPERATURES (SSTS), MODERATE POLEWARD OUTFLOW OFFSET BY LOW TO
MODERATE (10-15 KNOTS) VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTHEAST 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   FMEE: T3.0 - 45 KTS
   CIMSS ADT: 35 KTS AT 091815Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL CYCLONE 13S IS CURRENTLY FORECAST TO
TRACK GENERALLY WESTWARD OVER THE NEXT 36 HOURS UNDER THE STEERING
INFLUENCE OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) POSITIONED TO THE
SOUTHEAST. THE SYSTEM IS CURRENTLY BEING IMPACTED BY EASTERLY WIND
SHEAR BUT IS EXPECTED TO DECREASE ALLOWING FOR A GRADUAL
STRENGTHENING TREND. BY TAU 48, AN APPROACHING UPPER-LEVEL TROUGH
IS EXPECTED TO WEAKEN THE STR AND REPOSITION THE RIDGE TO A N-S
ORIENTATION. AS THIS OCCURS, THE SYSTEM WILL THEN TRACK IN A
SOUTHWESTERLY DIRECTION THROUGH TAU 72. ADDITIONALLY, THE
UPPER-LEVEL TROUGH WILL PROVIDE THE SYSTEM WITH INCREASED POLEWARD
OUTFLOW WHICH WILL RESULT IN A PEAK INTENSITY OF 60 KNOTS. BY TAU
96, ANOTHER STR WILL BUILD POLEWARD OF THE SYSTEM, WHICH WILL
ULTIMATELY BEGIN TO TURN THE SYSTEM IN A WEST-SOUTHWESTWARD DIRECTION
BY THE END OF THE FORECAST.


MODEL DISCUSSION: NUMERICAL TRACK MODEL GUIDANCE IS GENERALLY IN
GOOD AGREEMENT THROUGH TAU 72 WITH A 73 NM SPREAD IN TRACK
SOLUTIONS. BETWEEN TAU 96 AND 120 TRACK GUIDANCE SPREADS TO 485 NM.
THEREFORE, THE JTWC TRACK FORECAST IS ASSESSED WITH MEDIUM
CONFIDENCE GIVEN THE UNCERTAINLY BY THE END OF THE FORECAST. THE
INTENSITY GUIDANCE IS GENERALLY FAIR AGREEMENT THROUGH TAU 72, WITH
THE JTWC FORECAST FOLLOWING CLOSE TO THE MULTI-MODEL CONSENSUS
MEMBERS.  AFTER TAU 72 GUIDANCE DIVERGES WITH THE HWRF SHOWING A
PEAK INTENSITY OF 90 KNOTS, WHILE THE COAMPS-TC REPRESENTING THE
LOW END OF THE GUIDANCE ENVELOPE. THEREFORE, THE JTWC INTENSITY
FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE.  

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