MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W WARNING NR 01// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 17W (SEVENTEEN), LOCATED APPROXIMATELY 326 NM SOUTHWEST OF WAKE ISLAND, HAS TRACKED NORTHWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS PERSISTENT DEEP CONVECTION WITH FORMATIVE BANDS OVER THE NORTHERN AND SOUTHERN SEMI-CIRCLE OF A DEVELOPING LOW-LEVEL CIRCULATION CENTER. A 140336Z SSMI MICROWAVE IMAGE REVEALS BROKEN, BUT TIGHTLY-CURVED CONVECTIVE BANDING WRAPPING INTO THE CENTER. THE CURRENT POSITION IS BASED ON THE MSI, AFOREMENTIONED MICROWAVE IMAGE AND SATELLITE FIXES FROM PGTW AND RJTD WITH GOOD CONFIDENCE. THE INITIAL INTENSITY OF 25 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES. UPPER-LEVEL ANALYSIS INDICATES TD 17W IS LOCATED IN AN AREA OF MODERATE (15 TO 20 KNOT) VERTICAL WIND SHEAR (VWS) BEING OFFSET BY THE GOOD RADIAL OUTFLOW AS EVIDENT ON THE WATER VAPOR IMAGERY. TD 17W IS TRACKING UNDER THE INFLUENCE OF A WEAK STEERING ENVIRONMENT BETWEEN A SUBTROPICAL RIDGE (STR) TO THE NORTH AND A NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTH. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST PHILOSOPHY. B. SLOW AND/OR POSSIBLY QUASI-STATIONARY MOVEMENT IS EXPECTED OVER THE NEXT 48 HOURS AS THE SYSTEM REMAINS IN A WEAK STEERING ENVIRONMENT. BY TAU 48, THE STR IS FORECAST TO BUILD AND ASSUME THE STEERING PATTERN DRIVING TD 17W NORTHWESTWARD. CONCURRENTLY, MARGINALLY FAVORABLE CONDITIONS WILL PERSIST IN THE NEAR TERM, ALLOWING SLOW INTENSIFICATION. AFTER TAU 48, IN ADDITION TO FAVORABLE ENVIRONMENTAL CONDITIONS, IMPROVED UPPER-LEVEL OUTFLOW AND DECREASING VWS WILL ALLOW THE SYSTEM TO UNDERGO RAPID INTENSIFICATION (RI) THROUGH TAU 72. C. THE SYSTEM WILL MAINTAIN A NORTHWESTWARD TRAJECTORY. FAVORABLE CONDITIONS WILL PERSIST LEADING TO FURTHER RI. LIMITED MODEL GUIDANCE INDICATES A SIGNIFICANT DIFFERENCE IN THE TRACK AND TRACK SPEEDS IN THE SHORT TERM AND A LARGE SPREAD IN THE EXTENDED TAUS. FOR THIS REASON, THE JTWC TRACK FORECAST CONFIDENCE LEVEL IS LOW.// NNNN NNNN