MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN) WARNING NR 01// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 15W (FIFTEEN), LOCATED APPROXIMATELY 289 NM SOUTH-SOUTHWEST OF KADENA AB, OKINAWA, JAPAN HAS TRACKED EAST-NORTHEASTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A CONSOLIDATING LOW LEVEL CIRCULATION CENTER (LLCC) WITH CURVED CONVECTION WRAPPING INTO THE CENTER. A 311014Z SSMIS 91GHZ MICROWAVE IMAGE DEPICTS FRAGMENTED BANDING WRAPPING INTO THE LLCC FROM THE EASTERN AND NORTHERN PERIPHERIES. THE INITIAL POSITION IS BASED ON THE ABOVE IMAGERY AND IS SUPPORTED BY SATELLITE FIXES FROM PGTW AND RJTD WITH GOOD CONFIDENCE. THE CURRENT INTENSITY IS BASED ON DVORAK INTENSITY ESTIMATES OF T1.5 (25 KNOTS) FROM ALL REPORTING AGENCIES. THE SYSTEM IS LOCATED IN A FAVORABLE ENVIRONMENT WITH GOOD DIVERGENCE ALOFT AND LOW (10-15 KNOT) VERTICAL WIND SHEAR (VWS). SEA SURFACE TEMPERATURES ABOVE 30 CELSIUS ARE ALSO FAVORABLE FOR FURTHER DEVELOPMENT. TD 15W IS TRACKING ALONG THE NORTHERN PERIPHERY OF AN EXTENSION OF THE NEAR EQUATORIAL RIDGE (NER) LOCATED TO THE SOUTHEAST. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST PHILOSOPHY. B. TD 15W WILL CONTINUE TO TRACK NORTHEASTWARD UNDER THE INFLUENCE OF THE NER OVER THE NEXT 24 TO 36 HOURS. EXPECT THE CYCLONE TO GRADUALLY INTENSIFY DUE TO CONTINUED FAVORABLE ENVIRONMENTAL CONDITIONS; HOWEVER, DRY AIR AND SUBSIDENCE TO THE NORTH DUE TO AN UPPER LEVEL TROUGH EXTENDING DOWN OVER THE RYUKYU ISLANDS WILL TAPER SIGNIFICANT INTENSIFICATION. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH THIS PORTION OF THE FORECAST. BEYOND TAU 36, THE NER WILL RETROGRADE TO THE WEST CREATING A WEAK STEERING ENVIRONMENT WHICH WILL CAUSE A DECELERATION OF FORWARD MOTION AND POSSIBLY A PERIOD OF QUASI-STATIONARY OR ERRATIC MOTION. BEYOND TAU 48, THE COMBINED EFFECTS OF A BUILDING SUB-TROPICAL RIDGE TO THE EAST AND THE AFOREMENTIONED UPPER LEVEL TROUGH WILL FORCE THE SYSTEM NORTHWARD INTO A REGION OF INCREASING VWS AND SUBSIDENCE ALOFT. THESE FACTORS WILL BEGIN A WEAKENING TREND. C. IN THE EXTENDED FORECAST, TD 15W WILL CONTINUE TO MOVE NORTHWARD AND RAPIDLY WEAKEN AS IT MOVES FURTHER UNDER THE UPPER LEVEL TROUGH AND ENCOUNTERS VWS IN EXCESS OF 30 KNOTS. THE SYSTEM WILL FULLY DISSIPATE IN THE SEA OF JAPAN BY THE END OF THE FORECAST PERIOD. DYNAMIC MODEL GUIDANCE IS CURRENTLY STRUGGLING WITH THE LACK OF A DOMINANT STEERING MECHANISM NEAR TAU 36. AS A RESULT, NAVGEM, HWRF, AND THE JAPANESE ENSEMBLE SHOW A WEAKER SYSTEM TURNING NORTHWESTWARD, AT VARYING DEGREES, ACROSS THE NORTHERN RYUKYU ISLANDS AND INTO THE EAST CHINA SEA. THE REMAINING GUIDANCE IS IN LINE WITH THE CURRENT FORECAST WITH SOME NOTED DIFFERENCES IN THE FORWARD SPEED OF THE CYCLONE AS IT ACCELERATES NORTHWARD. DUE TO THE COMPLEX STEERING ENVIRONMENT BEYOND TAU 36 AND THE LACK OF OVERALL AGREEMENT IN THE MODELS, THERE IS LOW CONFIDENCE IN THE INITIAL JTWC TRACK FORECAST.// NNNN NNNN