WDXS32 PGTW 130900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DINGANI) WARNING NR 009// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.9S 73.4E INITIAL INTENSITY: 80 KTS GEOGRAPHIC REFERENCE: 913 NM EAST OF PORT LOUIS, MAURITIUS MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 25 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAGGED, FORMATIVE EYE WITH TIGHTLY CURVED SPIRAL BANDING. A 130412Z GMI 37GHZ MICROWAVE IMAGE REVEALS IMPROVED CONVECTIVE BANDING WRAPPING INTO A SMALL MICROWAVE EYE FEATURE, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. THE GMI 89GHZ IMAGE INDICATES THE UPPER-LEVEL CIRCULATION CENTER IS TILTED ABOUT 10NM SOUTHEAST OF THE LOW-LEVEL CIRCULATION CENTER. A 130407Z ASCAT-B BULLSEYE IMAGE WAS USED TO REFINE THE CURRENT WIND RADII. OVERALL, THE CONVECTIVE STRUCTURE HAS IMPROVED DUE TO THE ENHANCED, ROBUST POLEWARD OUTFLOW, CONSEQUENTLY, INTENSITY ESTIMATES HAVE INCREASED OVER THE PAST 12 HOURS. DVORAK ESTIMATES RANGE FROM T4.5 TO T5.5, HOWEVER, AN UNOFFICIAL PGTW EYE FIX NOW INDICATES A T5.0 (90 KNOTS). ADT AND AIDT ESTIMATES RANGE FROM 82-83 KNOTS WITH OPEN-AIIR ESTIMATES IN THE 85-90 KNOT RANGE. THE INITIAL INTENSITY IS ASSESSED AT 80 KNOTS FOR NOW, BUT MAY BE INCREASED IN THE NEXT 12 HOURS IF THE EYE CAN STRENGTHEN AND HOLD TOGETHER CONSISTENTLY. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS KNES: T5.5 - 102 KTS DEMS: T4.5 - 77 KTS FMEE: T4.5 - 77 KTS CIMSS SATCON: 88 KTS AT 130049Z CIMSS ADT: 82 KTS AT 130600Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 26-27 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM 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 (TC) 13S IS FORECAST TO TRACK SOUTH-SOUTHWESTWARD THROUGH TAU 72 ALONG THE WESTERN PERIPHERY OF THE STR. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE WITH ENHANCED POLEWARD OUTFLOW AND LOW VERTICAL WIND SHEAR (VWS) THROUGH TAU 12, WHICH MAY ALLOW FOR A SLIGHT INCREASE IN INTENSITY IF THE SYSTEM BECOMES VERTICALLY ALIGNED. AFTER TAU 12, STEADY WEAKENING WILL OCCUR AS VWS INCREASES TO HIGH LEVELS (30-45 KNOTS) WITH GRADUAL COOLING OF SST FROM 26C TO 24C AT TAU 72. AFTER TAU 72, TC 13S WILL DISSIPATE AS IT INTERACTS WITH THE STJ AND TRACKS OVER COOL SST (22-23C). MODEL DISCUSSION: DETERMINISTIC AND PROBABILISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 WITH A 90NM CROSS-TRACK SPREAD IN SOLUTIONS AT TAU 72. AFTER TAU 72, THERE IS INCREASING UNCERTAINTY IN THE JTWC FORECAST TRACK AS THE REMNANTS ARE EXPECTED TO TURN SHARPLY EAST-SOUTHEASTWARD WITHIN THE WESTERLIES. RELIABLE INTENSITY GUIDANCE SUPPORTS THE JTWC INTENSITY FORECAST WITH MEDIUM OVERALL CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN