MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 10W (TEN) WARNING NR 01// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 10W (TEN), LOCATED APPROXIMATELY 175 NM WEST-NORTHWEST OF YAP, HAS TRACKED WESTWARD AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS PERSISTENT CENTRAL CONVECTION WITH FORMATIVE BANDING ALONG THE SOUTHERN PERIPHERY WRAPPING INTO A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC). A SERIES OF RECENT MICROWAVE SATELLITE PASSES, INCLUDING A 170844Z SSMIS IMAGE, SUPPORT THE CURRENT POSITION WITH GOOD CONFIDENCE. THE CURRENT INTENSITY OF 30 KNOTS IS BASED ON CONSISTENT DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM IS LOCATED IN A FAVORABLE ENVIRONMENT WITH LOW (05 TO 10 KNOT) VERTICAL WIND SHEAR (VWS) AND EXCELLENT OUTFLOW AS EVIDENT IN THE WATER VAPOR IMAGERY. TD 10W IS CURRENTLY POSITIONED IN A WEAK STEERING ENVIRONMENT BETWEEN A DEEP-LAYER SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE NORTH AND A NEAR EQUATORIAL RIDGE (NER) TO THE SOUTHEAST. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST PHILOSOPHY. B. TD 10W IS EXPECTED TO TRACK SLOWLY WITH A POSSIBILITY OF QUASI- STATIONARY IN THE NEAR TERM DUE TO THE WEAK STEERING INFLUENCE BETWEEN TWO RIDGES. BY TAU 36, THE STR IS FORECAST TO BECOME THE DOMINANT STEERING PATTERN, TURNING THE SYSTEM TO THE NORTH. AROUND TAU 48, A MID-LATITUDE TROUGH DIGGING OVER SOUTHERN JAPAN IS EXPECTED TO WEAKEN THE STR, CAUSING TD 10W TO TURN MORE POLEWARD AND EVENTUALLY TRACK NORTHEASTWARD AS THE STR REORIENTS TO THE EAST OF THE SYSTEM. WARM SEA SURFACE TEMPERATURES (SST), FAVORABLE VWS AND WESTWARD DIFFLUENCE ALOFT ARE EXPECTED TO PERSIST, ALLOWING THE SYSTEM TO GRADUALLY INTENSIFY THROUGH TAU 72. C. IN THE EXTENDED TAUS, ANOTHER STR IS EXPECTED TO BUILD OVER EASTERN CHINA, DOMINATING THE STEERING PATTERN FOR THE REMAINDER OF THE FORECAST PERIOD. THE COMBINED EFFECTS OF FAVORABLE SST AND IMPROVED UPPER-LEVEL CONDITIONS WILL ALLOW THE SYSTEM TO FURTHER INTENSIFY, LEADING TO TYPHOON STRENGTH BY TAU 120. AVAILABLE DYNAMIC MODEL SOLUTIONS DIVERGE AT TAU 24 WITH A SPREAD OF 175 NM BETWEEN THE WESTERN AND EASTERN TRACKERS. HOWEVER, THE MAJORITY OF THE GUIDANCE DEPICTS A SLOW TRACK OVER THE NEXT 36. DUE TO THE SLOW AND/OR ERRATIC MOVEMENT IN THE NEAR TERM AND THE UNCERTAINTY IN THE EXACT TIMING OF THE NORTHWARD TURN, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST.// NNNN NNNN