WDPN31 PGTW 031500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W WARNING NR 03// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 06W (SIX), LOCATED APPROXIMATELY 192 NM EAST OF YAP, HAS TRACKED NORTH-NORTHWESTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A RECENT PGTW FIX ON INFRARED SATELLITE IMAGERY. THE INTENSITY OF 30 KNOTS IS BASED ON DVORAK SATELLITE INTENSITY ESTIMATES OF T=2.0 FROM PGTW AND KNES. TD 06W IS MOVING SLOWLY POLEWARD INTO A WEAKNESS IN THE SUBTROPICAL STEERING RIDGE INDUCED BY A MID-LATITUDE TROUGH PASSING TO THE NORTH. THE LLCC LIES EQUATORWARD OF AN UPPER-LEVEL RIDGE AXIS, IN AN AREA OF LOW TO MODERATE EASTERLY VERTICAL WIND SHEAR AND FAVORABLE POLEWARD OUTFLOW. DEEP CONVECTION HAS INCREASED DURING THE PAST SIX HOURS, PARTICULARLY OVER THE NORTHERN PORTION OF THE LOW LEVEL CIRCULATION CENTER (LLCC). A DEVELOPING UPPER-LEVEL POLEWARD OUTFLOW CHANNEL IS SUPPORTING THIS CONVECTIVE DEVELOPMENT. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS WARNING. B. TD 06W IS EXPECTED TO TRACK SLOWLY WEST-NORTHWESTWARD DURING THE UPCOMING 48 TO 72 HOUR PERIOD UNDER THE STEERING INFLUENCE OF WEAKENED SUBTROPICAL RIDGING TO THE NORTH. THEREAFTER, THE MID- LATITUDE TROUGH INDUCING THE RIDGE WEAKNESS WILL MOVE EASTWARD, ALLOWING THE SUBTROPICAL RIDGE TO REBUILD AND STEER TD 06W MORE RAPIDLY WEST-NORTHWESTWARD INTO THE PHILIPPINE SEA. VERTICAL WIND SHEAR AND UPPER-LEVEL OUTFLOW ARE EXPECTED TO REMAIN FAVORABLE, ENABLING TD 06W TO STEADILY INTENSIFY AFTER AN INITIAL PERIOD OF CONSOLIDATION OVER THE NEXT 6 TO 12 HOURS. NUMERIC MODELS REMAIN IN GOOD GENERAL AGREEMENT REGARDING TRACK DIRECTION, BUT LESS AGREEMENT REGARDING TRACK SPEED DURING THE FIRST 72 HOURS OF THE FORECAST. GIVEN UNCERTAINTY ASSOCIATED WITH THE EVOLUTION OF THE OBSERVED WEAKNESS IN THE STEERING RIDGE, THE NEAR-TERM JTWC FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS WITH LOW CONFIDENCE. C. IN THE EXTENDED TAUS, TD 06W WILL TRACK STEADILY WEST- NORTHWESTWARD UNDER THE STEERING INFLUENCE OF A BUILDING SUBTROPICAL RIDGE. THE SYSTEM SHOULD CONTINUE TO INTENSIFY AS ENVIRONMENTAL INFLUENCES REMAIN FAVORABLE. NUMERIC MODEL GUIDANCE IS IN FAIR AGREEMENT REGARDING TRACK DIRECTION AND SPEED IN THE EXTENDED TERM, LENDING HIGHER CONFIDENCE TO THE JTWC 96 AND 120 HOUR FORECAST POSITIONS.// NNNN