WDPN32 PGTW 180300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (TALIM) WARNING NR 02// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 06W (TALIM), LOCATED APPROXIMATELY 240 NM SOUTH-SOUTHWEST OF HONG KONG, HAS TRACKED EAST-NORTHEASTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS BANDING CONVECTION ALONG THE NORTHERN PERIPHERY OF THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS STARTED TO DEVELOP WITHIN THE PAST SIX HOURS. DEEP CONVECTION APPEARS TO BE BUILDING OVER THE LLCC, HOWEVER, BASED ON THE POORLY ORGANIZED LOW LEVEL STRUCTURE, THERE IS LOW CONFIDENCE IN THE LLCC POSITION. UPPER LEVEL ANALYSIS INDICATES A WEAK MESOSCALE ANTICYCLONE HAS STARTED BUILDING OVER THE LLCC, WITH MARGINAL VERTICAL WIND SHEAR (VWS) (15-20 KNOTS) HELPING TO PROVIDE AMPLE EQUATORWARD OUTFLOW. AN UPPER LEVEL SUBTROPICAL RIDGE (STR) IS BUILDING EASTWARD OVER SOUTHERN CHINA AND IS BEGINNING TO MOVE INTO THE SOUTH CHINA SEA (SCS). THIS RIDGE WILL HAMPER THE ANTICYCLONE FROM VENTING THE SYSTEM POLEWARD. THE SYSTEM HAS BEEN STEADILY TRACKING WITHIN THE LOW- TO MID-LEVEL GRADIENT FLOW. AS TY 05W (GUCHOL) CONTINUES TRACKING POLEWARD, A STR IS EXPECTED TO BECOME THE DOMINANT STEERING INFLUENCE. SEA SURFACE TEMPERATURES (SSTS) THROUGHOUT THE SCS ARE FAVORABLE FOR FURTHER DEVELOPMENT. THE INITIAL POSITION IS BASED ON THE MSI IMAGERY AND A FIX FROM PGTW. THE CURRENT INTENSITY OF 30 KNOTS IS BASED A 2.5/2.5 DVORAK ESTIMATE FROM PGTW. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 06W IS EXPECTED TO SLOWLY TRACK EASTWARD OVER THE NEXT 24 HOURS WITHIN THE LOW- TO MID-LEVEL GRADIENT FLOW AS THE STR BEGINS TO DOMINANT THE STEERING INFLUENCE. THROUGH TAU 48 TD 06W WILL INTENSITY AS FAVORABLE SSTS PERSIST THROUGHOUT THE SCS AND GOOD UPPER LEVEL SUPPORT ALLOWS THE SYSTEM TO VENT EQUATORWARD. THE FORECAST TRACK WILL TAKE TD 06W INTO TAIWAN AROUND TAU 48 AND WILL CAUSE THE SYSTEM TO WEAKEN DUE TO LAND INFLUENCE. ADDITIONALLY, THE SSTS DROP OFF WITHIN THE TAIWAN STRAIT, NORTH OF 25N. AS THE SYSTEM IS EXPECTED TO REACH STRONG TROPICAL STORM LEVELS, THE TRACK OVER TAIWAN WILL LIKELY CAUSE SIGNIFICANT ORGANIZATIONAL ISSUES WITHIN THE LLCC, REQUIRING TIME TO RE-DEVELOP ON THE LEEWARD SIDE OF TAIWAN. BY THIS TIME DECREASING SSTS AND INCREASING VWS WILL KEEP TD 06W FROM INTENSIFYING BY TAU 72. CONFIDENCE REMAINS LOW WITH THE FORECAST AS IT RELIES HEAVILY ON THE DEVELOPMENT OF THE STR, AND IF THE TIMING IS NOT CORRECT, TD 06W WILL HAVE MORE TIME WITHIN THE SCS TO INTENSIFY. C. IN THE EXTENDED FORECAST, TD 06W WILL CONTINUE TO TRACK ALONG THE NORTHWESTERN PERIPHERY OF THE RE-ESTABLISHED STR TOWARDS SOUTHWESTERN KYUSHU. DECREASING SSTS (22 TO 26 CELSIUS) AND INCREASING VWS WILL NOT ALLOW FOR FURTHER DEVELOPMENT. HOWEVER, THERE ARE INDICATIONS A WARM POOL OF WATER IS LOCATED TO THE NORTH OF KADENA AB, OKINAWA WITH SSTS NEAR 29 CELSIUS. THE IMPACT THIS WILL PROVIDE IN LIEU OF THE UNFAVORABLE UPPER LEVEL SUPPORT IS QUESTIONABLE. THE POSSIBILITY EXISTS IT WILL ALLOW TD 06W TO REMAIN A STRONG EXTRA-TROPICAL CIRCULATION AS EXTRA-TROPICAL TRANSITION BEGINS AROUND TAU 72 AND COMPLETES BY TAU 120. CONFIDENCE REMAINS LOW FOR THE EXTENDED TAUS BASED ON THE TIMING FOR THE STEERING STR DEVELOPMENT AND IMPACTS TO LLCC DEVELOPMENT BY THE WARM POOL OF SSTS. MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THE FORECAST, HOWEVER, THE MAJORITY OF THE GUIDANCE INDICATES THE STR SHOULD ALREADY BE HELPING THE STEERING OF THE SYSTEM. THIS FORECAST IS BASED PREDOMINANTLY ON THE CONSENSUS OF AVAILABLE MODEL GUIDANCE, HOWEVER THE TAU 96 AND 120 POSITIONS ARE SLIGHTLY FASTER THAN CONSENSUS TO KEEP WITH CLIMATOLOGICAL SPEEDS.// NNNN