MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING NR 01// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 04W (FOUR), LOCATED APPROXIMATELY 373 NM NORTH-NORTHWEST OF KAYANGEL, HAS TRACKED NORTHWESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS SITUATED JUST TO THE WEST OF A 281800Z PGTW SATELLITE FIX WITH FAIR CONFIDENCE. THE INTENSITY OF 25 KNOTS IS CONSISTENT WITH RECENT SUBJECTIVE DVORAK INTENSITY ESTIMATES FROM PGTW AND KNES AND FURTHER SUPPORTED BY EARLIER ASCAT DATA INDICATING 20-25 KNOT WINDS NEAR THE CENTER OF CIRCULATION. TD 04W IS TRACKING NORTHWESTWARD ALONG THE PERIPHERY OF A SUBTROPICAL STEERING RIDGE SITUATED TO THE NORTH AND EAST. FLARING DEEP CONVECTION HAS PERSISTED WITHIN THE SOUTHWESTERN QUADRANT OF THE LOW LEVEL CIRCULATION CENTER (LLCC) IN THE PRESENCE OF MODERATE NORTHEASTERLY VERTICAL WIND SHEAR (VWS). THE SEA SURFACE TEMPERATURE IN VICINITY OF THE LLCC IS VERY SUPPORTIVE AT 29 TO 30 DEGREES CELSIUS. 3. FORECAST REASONING. A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE FORECAST PHILOSOPHY. B. TD 04W IS EXPECTED TO CONTINUE TRACKING NORTHWESTWARD IN THE NEAR TERM UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGING TO THE NORTH AND EAST. PERSISTENT VWS SHOULD OFFSET THE FAVORABLE INFLUENCES OF PASSAGE OVER VERY WARM WATER AND WESTWARD DIFFLUENCE ALOFT, YIELDING A SLOW INTENSIFICATION RATE. NUMERICAL MODEL GUIDANCE DIVERGES REGARDING THE OVERALL SCENARIO, WITH A GROUPING CONSISTING OF THE GFS, HWRF AND NAVGEM SOLUTIONS REFLECTING A TRACK TOWARD SOUTHERN TAIWAN OR FARTHER TO THE SOUTH AND THE UKMET AND ECMWF PREDICTING A TRACK TOWARD NORTHER TAIWAN OR FARTHER TO THE NORTH AND EAST. THE FIRST 72 HOURS OF THE CURRENT FORECAST FAVORS THE SOUTHERN GROUPING, CONSISTENT WITH THE MODEL CONSENSUS. C. THE TRACK OF TD 04W IN THE EXTENDED RANGE IS HIGHLY UNCERTAIN, WITH MODEL SOLUTIONS RANGING FROM A STRAIGHT-RUNNING TRACK INTO NORTHERN PORTION OF THE SOUTH CHINA SEA TO A RECURVATURE TO THE EAST AND NORTH OF TAIWAN. GIVEN THAT TD 04W IS EXPECTED TO INTENSITY, ALBEIT SLOWLY, AND THE SUBTROPICAL STEERING RIDGE IS EXPECTED TO NEARLY MAINTAIN ITS CURRENT POSITION AND ORIENTATION THROUGHOUT THE FORECAST PERIOD, CONTINUED MOTION TOWARD THE NORTHWEST NEAR THE MIDDLE OF THE MODEL GUIDANCE ENVELOPE IS CONSIDERED MOST PROBABLE. THUS, THE CURRENT TRACK FORECAST IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS FOR THE EXTENDED PERIOD, BUT WITH LOW CONFIDENCE. VWS IS EXPECTED TO CONTINUE INFLUENCING THE SYSTEM EVEN INTO THE EXTENDED RANGE AND LAND INTERACTION IS ALSO DISTINCTLY POSSIBLE, SO SLOW INTENSITY CHANGE IS EXPECTED THROUGHOUT.// NNNN NNNN