WDPN32 PGTW 150900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 29W (CHAMPI) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 10.9N 158.4E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 809 NM EAST OF ANDERSEN AFB MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 13 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL DEPRESSION (TD) 29W HAS NOT CHANGED MUCH OVER THE PAST 6-12 HOURS AS IT MOVES WEST-NORTHWESTWARD. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH PERSISTENT DEEP CONVECTION ASSOCIATED WITH A MID-LEVEL CIRCULATION DISPLACED TO THE SOUTHWEST OF THE LLCC. OVERSHOOTING TOPS HAVE REACHED TEMPERATURES AS COLD AS -94 DEGREES CELSIUS. A 142320Z ASCAT-C PASS REVEALED A PATCH OF 30-KT WINDS CONFINED TO THE SOUTHWEST QUADRANT OF AN ELONGATED, ASYMMETRIC LLCC. A 150228Z AMSR3 PASS DID NOT REVEAL A WELL-DEFINED INNER CORE. THE SYSTEM IS TRAVERSING VERY WARM SEA SURFACE TEMPERATURES (SST) OF 29-30 DEGREES CELSIUS IN A MODERATELY SHEARED ENVIRONMENT WITH GOOD UPPER-LEVEL DIVERGENCE ALONG THE WESTERN PERIPHERY. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTLY OBSCURED LLCC IN MSI AND IS LOCATED NEAR THE TIGHT CLUSTER OF FIXES FROM PGTW, RJTD, AND RCTP. GIVEN THE RELATIVELY UNCHANGED CONVECTIVE STRUCTURE SINCE THE LAST CYCLE, THE INITIAL INTENSITY IS HELD AT 30 KTS WITH HIGH CONFIDENCE, WHICH IS SUPPORTED BY THE EARLIER ASCAT DATA AND THE UNANIMOUS T2.0 DVORAK CLASSIFICATIONS. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SOUTHERN FLANK OF A LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED NEAR 30N 160E AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T2.0 - 30 KTS RCTP: T2.0 - 30 KTS CIMSS SATCON: 36 KTS AT 150239Z CIMSS ADT: 32 KTS AT 150540Z CIMSS AIDT: 33 KTS AT 150540Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG WESTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: HIGH INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE OVERALL FORECAST TRACK HAS BEEN SHIFTED SLIGHTLY SOUTHWARD BY 18 NM AT TAU 60. FORECAST DISCUSSION: OVER THE PAST 12 HOURS, TD 29W HAS MOVED WEST-NORTHWESTWARD AT AN AVERAGE SPEED OF APPROXIMATELY 11 KTS. THE SYSTEM WILL GAIN SLIGHTLY MORE SPEED, AVERAGING 12-13 KTS THROUGH TAU 120, AS IT TRAVELS WEST-NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STR. A TROUGH PASSING WELL TO THE NORTH WILL ERODE THE RIDGE AROUND TAU 48. HOWEVER, A RIDGE LOCATED OVER THE EAST CHINA SEA WILL QUICKLY BUILD EASTWARD AND MAINTAIN THE WEST-NORTHWEST TRAJECTORY. OVER THE NEXT 60 HOURS, MODERATE VERTICAL WIND SHEAR (VWS) WILL PERSIST, WHILE THE SYSTEM TRAVELS OVER VERY WARM SST OF 29-30 DEGREES CELSIUS AND HIGH OCEAN HEAT CONTENT (OHC) OF NEAR 100 KJ PER CM2. INITIAL DEVELOPMENT WILL LIKELY BE GRADUAL DUE TO THE ASYMMETRIC AND VERTICALLY TILTED VORTEX. ONCE THE VORTEX BECOMES MORE SYMMETRICAL AND VERTICALLY ALIGNED, THE RATE OF INTENSIFICATION WILL INCREASE. SHEAR WILL EASE TO 10-15 KTS BY TAU 72, WHILE THE CIRCULATION MOVES OVER A REGION OF HIGH SST AND OHC BY TAU 96. THE FORECAST BRINGS TD 29W TO TYPHOON INTENSITY NEAR TAU 48, FOLLOWED BY A PERIOD OF RAPID INTENSIFICATION (RI) THROUGH TAU 96. THE FORECAST PEAKS AT 125 KTS AT TAU 96, CONSERVATIVELY ACCOUNTING FOR LESS PREDICTABLE INTERNAL DYNAMICS THAT COULD CAUSE INTENSITY FLUCTUATIONS. MODEL DISCUSSION: TRACK GUIDANCE IS GRADUALLY COMING INTO BETTER AGREEMENT, WITH THE CROSS-TRACK SPREAD DECREASING FROM 90 NM LAST CYCLE TO 70 NM THIS CYCLE AT TAU 60. THE SPREAD SPANS FROM ROTA TO A POINT SLIGHTLY SOUTH OF GUAM. THE BULK OF THE DYNAMICAL MODELS LIES ON THE POLEWARD SIDE OF THE GUIDANCE ENVELOPE, WHILE THE AI MODELS PREFER A MORE WESTWARD TRACK. GOOGLE DEEPMIND IS THE MOST WESTWARD SOLUTION, PASSING THE SYSTEM 14 NM SOUTH OF GUAM. ECMWF IS CLOSEST TO THE MULTI-MODEL CONSENSUS (CONW), WHILE GFS IS SLIGHTLY NORTH. THE OVERALL GUIDANCE ENVELOPE SHIFTED SOUTHWARD LAST CYCLE, AND THE SOLUTIONS THIS CYCLE REMAIN SIMILAR. THIS INCREASES CONFIDENCE IN A TRACK NEAR THE SOUTHERN MARIANA ISLANDS. THE JTWC FORECAST HAS THEREFORE BEEN NUDGED SOUTHWARD BY 18 NM AT TAU 60 AND IS POSITIONED SOUTH OF CONW, BUT 8 NM NORTH OF THE AI-MODEL MEAN AND 25 NM NORTH OF THE GOOGLE DEEPMIND SOLUTION. MODEST SPREAD EXISTS AMONG THE INTENSITY AIDS. DEEPMIND AND COAMPS-TC ARE THE MOST AGGRESSIVE SOLUTIONS, DEPICTING 95-110 KTS AT TAU 60 AND 135 KTS AFTER TAU 72. GFS IS SLOWER AND WEAKER OVERALL. THE JTWC INTENSITY FORECAST ACCOUNTS FOR THE ASYMMETRIC AND TILTED VORTEX, CALLING FOR A SLOWER INITIAL RATE OF INTENSIFICATION THROUGH TAU 48, FOLLOWED BY RI THROUGH TAU 96. THIS FORECAST LIES NEAR THE CENTER OF THE GUIDANCE ENVELOPE THROUGH TAU 48, THEN GRADUALLY TRENDS TOWARD THE HIGHER END OF THE ENVELOPE. IF TD 29W CAN ACHIEVE AXISYMMETRIZATION QUICKLY, THE STORM MAY INTENSIFY TO WELL OVER 80 KTS BY THE TIME IT PASSES NEAR THE MARIANA ISLANDS. FURTHERMORE, A PEAK HIGHER THAN 125 KTS REMAINS WELL WITHIN THE REALM OF POSSIBILITIES, GIVEN THE INCREASINGLY FAVORABLE ENVIRONMENTAL CONDITIONS TOWARD THE END OF THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN