WDXS32 PGTW 122100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DINGANI) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.8S 74.4E INITIAL INTENSITY: 75 KTS GEOGRAPHIC REFERENCE: 980 NM EAST OF PORT LOUIS, MAURITIUS MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 26 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A COMPACT SYSTEM THAT HAS IMPROVED ITS OVERALL CONVECTIVE SIGNATURE AS THE CENTRAL CONVECTION DEEPENED AND MAINTAINED A RAGGED BUT DEFINED EYE OVER THE PAST 12HRS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE IN THE EIR LOOP. THE INITIAL INTENSITY IS ALSO PLACED WITH HIGH CONFIDENCE BASED ON THE MAJORITY AND HIGH END OF AGENCY AND AUTOMATED DVORAK ESTIMATES AND CONSISTENT WITH THE 12-HR CONVECTIVE IMPROVEMENT. ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH STRONG POLEWARD OUTFLOW, LIGHT TO MODERATE VERTICAL WIND SHEAR AND WARM SSTS. INITIAL WIND RADII BASIS: PERSISTENCE. CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.0 - 65 KTS KNES: T4.5 - 77 KTS DEMS: T4.0 - 65 KTS CIMSS ADT: 74 KTS AT 121500Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 27-28 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH 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 DINGANI WILL TRACK GENERALLY SOUTHWESTWARD UNDER THE STEERING STR. AFTER TAU 96, IT WILL RECURVE SOUTHWESTWARD IN RESPONSE TO AN APPROACHING MID-LATITUDE SHORTWAVE TROUGH. VWS IS EXPECTED TO GRADUALLY INCREASE AND SST TO SLOWLY COOL AS THE SYSTEM TRACKS POLEWARD, RESULTING IN STEADY WEAKENING. BY TAU 120, TC DINGANI WILL BE BELOW JTWC WARNING CRITERIA AT 30KTS AS IT TRACKS WELL SOUTH OF RODRIGUES ISLAND, MAURITIUS. THERE IS A DISTINCT POSSIBILITY THAT TS 13S WILL DISSIPATE SOONER THAN TAU 120 DUE TO THE HIGH VWS AND COOL SSTS. MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT UP TO TAU 72 WITH A GRADUAL AND EVEN SPREAD TO 204NM; AFTERWARD, THE MEMBERS SIGNIFICANTLY AND ERRATICALLY SPREAD OUT TO OVER 850NM BY TAU 120, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST UP TO TAU 72, THEN LOW AFTERWARD. THERE IS MEDIUM CONFIDENCE IN THE INTENSITY FORECAST UP TO TAU 72, THEN LOW AFTERWARD DUE TO THE UNCERTAINTY IN THE INTENSITY AFTER TAU 72, COINCIDENT WITH THE ERRATIC SPREAD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN