WDPN31 PGTW 131500 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (BANYAN) WARNING NR 15 (RELOCATED)// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TROPICAL DEPRESSION (TD) 23W (BANYAN), LOCATED APPROXIMATELY 225 NM WEST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. A POSITION FIX OF MUCH HIGHER CONFIDENCE WAS MADE AT 131200Z. THE NEW POSITION RESULTS IN A FORECAST TRACK APPROXIMATELY 95 MILES EAST OF BUT PARALLEL TO THE PREVIOUS TRACK. THE NEW INITIAL POSITION DOES NOT RESULT IN ANY CHANGE TO THE OVERALL TRACK OR INTENSITY FORECAST. THE NEW PGTW FIX IS BASED ON TWO MICROWAVE SERIES (A 131118Z CORIOLIS AND A 131137Z SSMIS) ALONG WITH THREE SHIP REPORTS. ANIMATED INFRARED SATELLITE IMAGERY (MSI) CONTINUES TO SHOW A BROAD AND WEAKLY ORGANIZED SYSTEM WITH SHALLOW CONVECTION IN ALL QUADRANTS. CONVECTION IS CONSOLIDATING CLOSER TO THE CORE AND RECENT AMSU RADIAL CROSS SECTIONS REVEAL THE RETURN OF A WEAK MID-LEVEL WARM ANOMALY. THE CURRENT INTENSITY ASSESSMENT IS BASED ON A COMBINATION OF DVORAK ESTIMATES FROM PGTW AND RJTD, THE MICROWAVE SIGNATURES, AND EXTRAPOLATIONS FROM SHIP REPORTS ON THE PERIMETER OF THE SYSTEM. THE PGTW 130000Z UPPER LEVEL STREAMLINE ANALYSIS DEPICTS AN ANTICYCLONE OVER NORTHEASTERN LUZON. TD 23W EXISTS UNDER A MILDLY DIFFLUENT REGION ASSOCIATED WITH THE SOUTHWESTERN QUADRANT OF THE ANTICYCLONE. VERTICAL WIND SHEAR IS APPROXIMATELY 15 KNOTS AND SEA SURFACE TEMPERATURE IS 29 DEGREES, BUT SEA SURFACE TEMPERATURES FALL SIGNIFICANTLY NORTH OF 15 DEGREES NORTH LATITUDE. ANIMATED WATER VAPOR IMAGERY REVEALS UNIMPEDED OUTFLOW IN ALL QUADRANTS. TD 23W IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A LOW- TO MID-LEVEL STEERING RIDGE, WHICH IS WEAKENING AND RE-ORIENTING TO THE NORTHEAST IN RESPONSE TO A DEEP AND VIGOROUS MID-LATITUDE TROUGH DIGGING INTO EASTERN CHINA. 3. A. THE FORECAST PHILOSOPHY HAS NOT CHANGED SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. AS THE TROUGH DEEPENS OVER SOUTHEASTERN CHINA, THE STEERING RIDGE WILL WEAKEN AND RE-ORIENT TO THE EAST. AS THE RIDGE WEAKENS, ITS INFLUENCE ON TD 23W WILL WANE AND THE STORM WILL SLOW NEAR TAU 24. A HIGH AMPLITUDE RIDGE BUILDING OVER CHINA WILL DRIVE THE TROUGH OVER TAIWAN AND SUPPORT A NEW AND STRONG LOW- TO MID- LEVEL STEERING RIDGE OVER THE SOUTHERN COAST OF CHINA. THE NEW STEERING RIDGE WILL PICK UP TD 23W AND DRIVE IT ON A MORE WESTWARD COURSE TOWARDS THE COAST OF VIETNAM. SEA SURFACE TEMPERATURES WILL FALL TO THE MINIMAL SUPPORTIVE VALUES OF 26 TO 27 DEGREES WHILE VERTICAL WIND SHEAR WILL REMAIN NEAR 15 KNOTS. THEREFORE TD 23W WILL REACH PEAK INTENSITY BETWEEN TAU 24 AND 48 AS IT SLOWS BEFORE MAKING ITS WESTWARD TURN. AFTER THE WESTWARD TURN, TD 23W WILL WEAKEN SLOWLY ALONG TRACK. MODEL GUIDANCE HAS BEEN MORE ERRATIC THAN USUAL DUE TO THE LOW INTENSITY OF THE SYSTEM BUT HAS COME INTO MUCH BETTER AGREEMENT OVER THE PAST 36 HOURS. THE JTWC TRACK FORECAST STAYS CLOSE TO CONSENSUS THROUGH TAU 72, WHILE THE INTENSITY FORECAST IS A NOTCH HIGHER THAN GUIDANCE DUE TO THE IMPROVING OUTFLOW SITUATION AND THE OBSERVED CONSOLIDATION OF THE CONVECTION DURING THE PAST 12 HOURS. C. THE ANTICYCLONE WILL SETTLE ALONG THE SOUTHERN CHINESE COAST AND DRIVE A STEADILY WEAKENING TD 23W INTO VIETNAM. THE EXTENDED RANGE TRACK FORECAST STAYS AHEAD OF CONSENSUS AND CLOSE TO ECMWF, AS CONSENSUS IS BEING SLOWED BY GFS AND WBAR, BOTH OF WHICH DEPICT A NEAR-TERM TRACK TOWARDS TAIWAN.// NNNN