WDPN31 PGTW 090300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 05W (PEIPAH) WARNING NR 25// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 05W (PEIPAH), LOCATED APPROXIMATELY 672 NM SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD LOW-LEVEL CIRCULATION CENTER (LLCC) WITH MULTIPLE VORTICES ROTATING ABOUT A CENTROID (WHICH IS THE INITIAL POSITION). MSI SHOWS A WEAK VORTICE NEAR 7.3N 131.4E, WHICH IS TRACKING EAST-NORTHEASTWARD AND WEAKENING OVER THE PAST SIX HOURS. DESPITE A SLIGHT IMPROVEMENT IN CONVECTIVE STRUCTURE, THE LLCC REMAINS BROAD AND THE CENTER REMAINS DIFFICULT TO PINPOINT. A 082300Z SSMIS IMAGE DEPICTS THE PRIMARY CURVED CONVECTIVE BAND OVER THE NORTHERN SEMI-CIRCLE WITH WEAK BANDING OVER THE SOUTHWEST QUADRANT AND SUPPORTS THE INITIAL POSITION WITH POOR CONFIDENCE. BASED ON THE IMPROVED, PERSISTENT BANDING AND DVORAK INTENSITY ESTIMATES OF 30 KNOTS, THE INITIAL INTENSITY IS ASSESSED AT 30 KNOTS. UPPER-LEVEL ANALYSIS REVEALS A MARGINAL ENVIRONMENT CHARACTERIZED BY MODERATE (20 KNOTS) EASTERLY VERTICAL WIND SHEAR OFFSET BY STRONG DIFFLUENCE AND GOOD POLEWARD OUTFLOW. TD 05W IS SITUATED WITHIN A WEAK STEERING ENVIRONMENT AND IS TRACKING ERRATICALLY BUT SLOWLY NORTHWESTWARD TOWARD A BREAK IN THE SUBTROPICAL RIDGE. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 05W IS FORECAST TO REMAIN IN THE WEAK STEERING ENVIRONMENT THROUGH TAU 36 BUT IS FORECAST TO TRACK SLOWLY NORTHWESTWARD TOWARD THE WEAKNESS IN THE SUBTROPICAL RIDGE (STR). DYNAMIC GUIDANCE IS IN FAIR AGREEMENT WITH SOLUTIONS INDICATING NORTHWESTWARD TRACKS, HOWEVER, GFS AND ECMWF NOW SHOW A QUASI-STATIONARY TRACK THROUGH TAU 48. THE JTWC FORECAST TRACK ALSO REFLECTS A VERY SLOW TRACK THROUGH TAU 48 AND IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS. TD 05W SHOULD SLOWLY INTENSIFY TO A PEAK OF 35 KNOTS BY TAU 36 AS THE TRACK SPEEDS INCREASE AND AS THE SYSTEM TRACKS INTO LOWER VERTICAL WIND SHEAR WHILE MAINTAINING ROBUST POLEWARD OUTFLOW. C. IN THE EXTENDED TAUS, TD 05W IS EXPECTED TO TURN WEST- NORTHWESTWARD AND TO ACCELERATE AS THE STR RE-BUILDS NORTH OF THE SYSTEM. 05W SHOULD WEAKEN GRADUALLY PRIOR TO TRACKING OVER THE PHILIPPINES AND IS FORECAST TO DISSIPATE BY TAU 96. DUE TO THE UNCERTAINTY IN THE INITIAL POSITION AND SHORT-TERM MOTION AS WELL AS MAJOR TRACK SPEED DIFFERENCES BETWEEN THE DYNAMIC MODELS, THERE IS A HIGH DEGREE OF UNCERTAINTY AND, CONSEQUENTLY, LOW CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN