WDPN32 PGTW 130300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 24W (TWENTYFOUR) WARNING NR 01// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 24W (TWENTYFOUR), LOCATED APPROXIMATELY 155 NM NORTHWEST OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 22 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS DEEPENED AS FORMATIVE BANDS, ALBEIT STILL FRAGMENTED, WRAPPED TIGHTER INTO A BROAD LOW LEVEL CIRCULATION CENTER (LLCC) THAT IS OBSCURED BY A CENTRAL DENSE OVERCAST FEATURE. THE SAME ANIMATION INDICATES THE MAIN BULK OF THE CONVECTION IS SHEARED WESTWARD OF THE LLCC. THE INITIAL POSITION IS BASED ON THE MSI LOOP AND EXTRAPOLATED FROM SURFACE OBSERVATIONS FROM GUAM AND SAIPAN WITH LOW CONFIDENCE. THE INITIAL INTENSITY OF 25 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS SOUTH OF THE RIDGE AXIS IN AN AREA OF MODERATE 20-KNOT VERTICAL WIND SHEAR (VWS). HOWEVER, THE VWS IS EASILY OFFSET BY A NEAR-RADIAL OUTFLOW. THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING BULLETIN AND SETS THE FORECAST PHILOSOPHY. B. TD 24W WILL TRACK WESTWARD UNDER THE INFLUENCE OF THE STR THROUGHOUT THE FORECAST PERIOD. AS IT TRAVERSES THE WARM PHILIPPINE SEA (WITH SSTS 29-31 CELSIUS), THE VWS IS EXPECTED TO RELAX. THIS COUPLED WITH A CONTINUED VIGOROUS OUTFLOW WILL PROMOTE STEADY INTENSIFICATION, REACHING TYPHOON STRENGTH BY TAU 72. C. BEYOND TAU 72, THE SYSTEM WILL APPROACH NORTHERN LUZON, PHILIPPINES. ENHANCED OUTFLOW, IN ADDITION TO THE AFOREMENTIONED FAVORABLE CONDITIONS, WILL PROMOTE A RAPID INTENSIFICATION - REACHING 115 KNOTS, POSSIBLY STRONGER, BY END OF FORECAST. THE AVAILABLE DYNAMIC MODELS ARE IN GOOD AGREEMENT WITH SOME BIFURCATION TOWARDS THE END OF THE FORECAST. HOWEVER, GIVEN THE UNCERTAINTY IN THE INITIAL POSITION AND STORM MOTION, THERE IS OVERALL LOW CONFIDENCE TO THE INITIAL JTWC FORECAST TRACK.// NNNN