MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (LINGLING) WARNING NR 1// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 15W (LINGLING), LOCATED APPROXIMATELY 282 NM EAST OF MANILA, PHILIPPINES, HAS TRACKED NORTH-NORTHWESTWARD AT 16 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A BROAD AND CONSOLIDATING SYSTEM WITH A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION AND FLARING DEEP CONVECTION FORMING A RING AROUND MOST OF THE PERIPHERY OF THE SYSTEM. A 012201Z CORIOLIS 37 GHZ MICROWAVE IMAGE SHOWED A BROAD BAND OF DEEP CONVECTION ON THE EASTERN PERIPHERY AND WEAKER FORMATIVE BANDING ON THE WESTERN SIDE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE CORIOLIS MICROWAVE IMAGE AND AN ANALYSIS OF ASCAT AMBIGUITIES FROM A 020028Z ASCAT-B PASS. THE INITIAL INTENSITY IS ASSESSED AT 30 KNOTS BASED ON A DVORAK CURRENT INTENSITY ESTIMATE OF T2.0 (30 KNOTS) FROM PGTW, SUPPORTED BY THE ASCAT PASS, WHICH SHOWED A BROAD AREA OF 25-30 KNOT WINDS IN THE NORTHEASTERN QUADRANT. ENVIRONMENTAL ANALYSIS REVEALS THE SYSTEM LIES IN A FAVORABLE ENVIRONMENT, WITH LOW (5-10 KNOTS) VWS, WARM SSTS (29-30 CELSIUS) AND MODERATE POLEWARD AND EQUATOR OUTFLOW. TD 15W IS TRACKING GENERALLY NORTHWARD ALONG THE WESTERN PERIPHERY OF A SOUTHWARD EXTENSION OF THE SUBTROPICAL RIDGE (STR) CENTERED EAST OF JAPAN. 3. FORECAST REASONING. A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE FORECAST PHILOSOPHY. B. OVER THE NEXT 36 HOURS, TD 15W WILL CONTINUE TRACKING NORTH-NORTHWEST ALONG THE WESTERN PERIPHERY OF AN EXTENSION OF THE STR CENTERED FAR TO THE NORTH. AFTER TAU 36, THE STR EXTENSION PINCHES OFF TO FORM A NEAR-EQUATORIAL RIDGE (NER) CENTERED OVER THE PHILIPPINES RESULTING IN A WEAKENING IN THE OVERALL RIDGE PATTERN. THIS WILL ALLOW TD 15W TO SLOW DOWN SIGNIFICANTLY AS IT MOVES NORTHWARD TO THE EAST OF TAIWAN. BY TAU 72, THE STEERING STR BEGINS TO ERODE AHEAD OF AN APPROACHING DEEP-LAYER TROUGH, AND REORIENTS TO A NORTH-SOUTH AXIS, ALLOWING TD 15W TO TURN NORTH-NORTHEAST AND ACCELERATE THROUGH TAU 72. TD 15W IS FORECAST TO STEADILY INTENSIFY UNDER FAVORABLE ENVIRONMENTAL CONDITIONS OF LOW VWS, WARM SSTS AND STRONG UPPER-LEVEL OUTFLOW, PEAKING AT 60 KNOTS BY TAU 72. C. AFTER TAU 72, A DEEP TROUGH IS FORECAST TO DIG OVER EASTERN CHINA, WHICH WILL ERODE THE STEERING STR AND ALLOW THE SYSTEM TO TURN ONTO A MORE NORTHEASTWARD TRACK TOWARDS THE SOUTHERN YELLOW SEA THROUGH TAU 120. THE SYSTEM IS EXPECTED TO MAINTAIN INTENSITY OF 60 KNOTS FROM TAU 72 TO TAU 96. THEREAFTER DRY AIR ENTRAINMENT, COOLER SSTS AND INCREASING VWS WILL ALL CONSPIRE TO WEAKEN THE SYSTEM. DYNAMIC MODEL GUIDANCE IS IN POOR AGREEMENT THROUGHOUT THE FORECAST PERIOD, BUT PARTICULARLY BEYOND TAU 48, WITH OVER 1100 NM ALONG TRACK DIFFERENCES BETWEEN GFS AND NAVGEM BY TAU 120. THERE IS ALSO SIGNIFICANT CROSS TRACK DISAGREEMENT BETWEEN GFS ON THE EASTERN SIDE, AND ECMWF ON THE WESTERN PORTION OF THE ENVELOPE. THE OFFICIAL TRACK LIES CLOSE TO THE ECMWF THROUGH TAU 72, THEN INSIDE AND SLOWER THAN THE MULTIMODEL CONSENSUS THROUGH TAU 120. AN ALTERNATE SCENARIO FAVORED BY THE GFS MODEL RESULTS IN THE SYSTEM MOVING INTO A WEAK STEERING ENVIRONMENT BETWEEN THE STR AND NER AND DRIFTING VERY SLOWLY NORTHWARD THROUGH TAU 72, THEN MOVING JUST NORTH OF ISHIGAKIJIMA BY TAU 120. WITH THE SIGNIFICANT DISAGREEMENT IN THE GUIDANCE AND POTENTIAL ALTERNATE SCENARIO, THERE IS OVERALL LOW CONFIDENCE IN THE FORECAST TRACK.// NNNN NNNN