WDPN31 PGTW 290300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 10W (SAOLA) WARNING NR 05// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 10W (SAOLA), LOCATED APPROXIMATELY 340 NM NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTH-NORTHWESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS AN ELONGATED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH TWO DISTINCT CIRCULATION CENTERS ROTATING ABOUT A CENTROID. THE EASTERN CIRCULATION CENTER IS LOCATED NEAR 17.9N 126.6E AND THE WESTERN CIRCULATION CENTER IS LOCATED NEAR 17.7N 125.2E. THE INITIAL POSITION IS BASED ON THE CENTROID, WHICH IS BETWEEN THE TWO CIRCULATION CENTERS. A 290057Z METOP-A IMAGE INDICATES THAT THE PRIMARY CONVECTIVE BAND IS LOCATED OVER THE WESTERN PERIPHERY OF THE LLCC WITH A WEAKER BAND OVER THE EASTERN PERIPHERY. A 290059Z ASCAT IMAGE ALSO CONFIRMS THE ELONGATED NATURE OF THE LLCC WITH 30 TO 35 KNOT WINDS OVER THE SOUTHERN SEMI-CIRCLE. BASED ON THIS DATA, THERE IS FAIR CONFIDENCE IN THE INITIAL POSITION. THE INITIAL INTENSITY IS BASED ON THE ASCAT DATA AS WELL AS DVORAK ESTIMATES RANGING FROM 35 (PGTW, KNES) TO 55 KNOTS (RJTD). THE RJTD DVORAK ESTIMATE APPEARS TOO HIGH CONSIDERING THE ASCAT DATA AND THE LLCC'S ELONGATED SIGNATURE. ANIMATED WATER VAPOR IMAGERY INDICATES IMPROVED, NEAR- RADIAL OUTFLOW. TS 10W IS CURRENTLY TRACKING NORTHWARD ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR). THE 28/12Z 500 MB ANALYSIS DEPICTS A WEAK EASTERN STR AND A STRONG EAST-WEST ORIENTED STR POSITIONED OVER EASTERN CHINA AND JAPAN. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING. B. TS 10W IS FORECAST TO TRACK SLOWLY NORTH-NORTHWESTWARD THROUGH TAU 72 UNDER THE STEERING INFLUENCE OF THE EASTERN STR. DYNAMIC MODEL GUIDANCE IS IN FAIR AGREEMENT WITH TWO DISTINCT GROUPINGS. NOGAPS AND GFS REMAIN ON THE EASTERN EDGE OF THE ENVELOPE AND SHOW A NORTH-NORTHEASTWARD TRACK THROUGH TAU 48, WHICH IS INCORRECT DUE TO ERRONEOUS INTERACTION WITH ANOTHER SYSTEM DEVELOPING SOUTH OF JAPAN. THE SECOND GROUPING OF MODELS (JGSM, ECMWF, UKMO AND WBAR) PRESENT A MORE CONSISTENT FORECAST (AND TIGHT GROUPING) TOWARD TAIWAN WITHOUT ANY INDICATIONS OF ERRONEOUS CYCLONE INTERACTION. TS 10W IS EXPECTED TO INTENSIFY THROUGH THE FORECAST PERIOD TO A PEAK OF 95 KNOTS BY TAU 72. C. IN THE EXTENDED TAUS, THERE IS LARGE SPREAD IN THE DYNAMIC MODEL TRACKERS WITH NOGAPS AND GFS TRACKING THE SYSTEM NORTH OF TAIWAN AND THE REMAINDER OF THE MODELS TRACKING THE SYSTEM OVER TAIWAN. THERE IS LOW OVERALL CONFIDENCE IN THE FORECAST TRACK DUE TO UNCERTAINTIES IN LOCATING THE SYSTEM CENTER AS WELL AS POTENTIAL TRACK ERROR DUE TO THE WEAK STEERING INFLUENCE THROUGH TAU 72. AFTER TAU 72, THERE IS INCREASED CONFIDENCE IN THE TRACK FORECAST AS THE STEERING INFLUENCE TRANSITIONS TO THE STRONG STR POSITIONED OVER CHINA AND JAPAN.// NNNN