MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (SIXTEEN) WARNING NR 05// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 16W (SIXTEEN), LOCATED APPROXIMATELY 205 NM WEST-NORTHWEST OF NAVSTA GUAM, HAS TRACKED WESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY INDICATES DEEP CONVECTION INCREASING IN AREAL EXTENT, HOWEVER, THE BULK OF THE CONVECTION IS CONFINED TO THE SOUTHERN SEMI- CIRCLE OF THE LOW-LEVEL CIRCULATION CENTER (LLCC) DUE TO NORTHERLY VERTICAL WIND SHEAR (VWS). A 091538Z GCOM 36GHZ IMAGE AND A 091720Z AMSU-B 89GHZ IMAGE BOTH DEPICT AN EXPOSED LLCC WITH A CURVED DEEP CONVECTIVE BAND OVER THE SOUTHWEST QUADRANT OF THE LLCC. THERE IS FAIR CONFIDENCE IN THE CURRENT POSITION BASED ON THE GCOM 36GHZ IMAGE, WHICH SHOWS CONVECTIVE BANDING WRAPPING INTO AN ELONGATED BUT DEFINED LLCC. THE CURRENT INTENSITY HAS BEEN HELD AT 30 KNOTS BASED ON THE CONVECTIVE SIGNATURE, A RECENT ASCAT IMAGE AND A PGTW DVORAK ESTIMATE OF T2.0 (30 KNOTS). ENVIRONMENTAL ANALYSIS INDICATES A MARGINALLY-FAVORABLE ENVIRONMENT WITH LOW (5-10 KNOT) VWS, WEAK RADIAL OUTFLOW, AND WARM (29C) SST. THE SYSTEM HAS STARTED TO TRACK WESTWARD TO WEST-NORTHWESTWARD UNDER THE STEERING INFLUENCE OF A BUILDING LOW LEVEL SUBTROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 16W IS FORECAST TO TRACK NORTHWESTWARD UNDER THE BUILDING STR THROUGHOUT THE FORECAST PERIOD. THE GENERALLY FAVORABLE ENVIRONMENTAL CONDITIONS WILL ALLOW FOR A STEADY INTENSIFICATION OVER THE NEXT 36 HOURS. AFTERWARDS, INCREASED VWS DUE TO NORTHEASTERLY FLOW ASSOCIATED WITH THE EASTERN EDGE OF AN UPPER LEVEL STR POSITIONED OVER CHINA WILL TEMPER THE RATE OF INTENSIFICATION. BEYOND TAU 48, THIS RIDGE WILL WEAKEN, DECREASING THE VWS ONCE AGAIN. DYNAMIC MODEL GUIDANCE REMAINS IN FAIRLY GOOD AGREEMENT DURING THIS PORTION OF THE FORECAST, WITH ONLY SMALL DIFFERENCES IN THE FORWARD SPEED OF THE SYSTEM. C. IN THE EXTENDED FORECAST PERIOD, TD 16W WILL BEGIN TO TURN POLEWARD AS IT TRACKS ALONG THE SOUTHWEST PERIPHERY OF THE STR. BEYOND TAU 72, IMPROVED VWS AND OUTFLOW ASSOCIATED WITH A MID- LATITUDE TROUGH APPROACHING FROM THE WEST, COMBINED WITH INCREASED SSTS AND HIGH OCEAN HEAT CONTENT, WILL SUPPORT AN INCREASED INTENSIFICATION RATE WITH THE POSSIBILITY OF RAPID INTENSIFICATION. THERE IS A LARGE DEGREE OF UNCERTAINTY IN THE EXTENDED TAUS WITH A 450-NM SPREAD IN MODEL TRACKER SOLUTIONS. WITH THE EXCEPTION OF THE UKMET, ALL THE OTHER MODELS SUPPORT A RE-CURVE SCENARIO WITH SIGNIFICANT DIFFERENCES IN THE RE-CURVE POINT AND TRACK SPEEDS. MODEL FIELDS INDICATE AN APPROACHING SHORTWAVE TROUGH WILL ERODE THE STR OVER EASTERN CHINA ALLOWING TD 16W TO RE-CURVE POLEWARD AS IT TRACKS ALONG THE WESTERN PERIPHERY OF THE EASTERN STR, POSITIONED SOUTH OF JAPAN. TRACK SPEEDS LIKELY WILL REMAIN SLOW THROUGH TAU 120 DUE TO THE LACK OF A DYNAMIC, DEEP SHORTWAVE TROUGH AND WEAK BAROCLINICITY. THE JTWC TRACK FORECAST IS POSITIONED NEAR THE MULTI- MODEL CONSENSUS (CONW) THROUGH TAU 72 AND THEN RIGHT OF CONW FAVORING ALL OF THE GLOBAL MODELS WHICH SHOW A RECURVE SCENARIO. DUE TO INCREASING UNCERTAINTY AND LARGE MODEL SPREAD IN THE RE-CURVE PHASE, THERE IS NOW LOW CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN NNNN