MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) WARNING NR 03// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) TROPICAL DEPRESSION 20W, LOCATED APPROXIMATELY 75 NM SOUTH-SOUTHEAST OF PAGAN, CNMI, HAS TRACKED WEST-NORTHWESTWARD AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS FORMATIVE BANDS FEEDING-IN MOSTLY FROM THE SOUTH HAVE MAINTAINED DEEP CONVECTIVE CELLS ALTHOUGH THE CELLS REMAIN FRAGMENTED AND POORLY ORGANIZED. ADDITIONALLY, AT LEAST TWO OTHER VORTICES APPEAR TO BE OSCILLATING NORTHEAST OF THE MAIN LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS BASED ON THE ABOVE ANIMATION AND EXTRAPOLATED FROM A NOTCH FEATURE ON A 302257Z SSMI-S MICROWAVE IMAGE. THE INITIAL INTENSITY IS AVERAGED FROM OBJECTIVE AND SUBJECTIVE DVORAK ESTIMATES FROM CIMS, PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS UNDER A RIDGE AXIS IN AN AREA OF LIGHT (05-10 KNOT) VERTICAL WIND SHEAR (VWS). ANIMATED WATER VAPOR IMAGERY SHOWS ENHANCED POLEWARD OUTFLOW INTO A TUTT CELL NORTH OF THE RIDGE AXIS. THERE IS ALSO AMPLE EQUATORWARD OUTFLOW ENHANCED BY STRONG NORTHEASTERLY WIND FLOW AWAY FROM THE RIDGE AXIS. THE CYCLONE IS CURRENTLY TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. A MID-LATITUDE TROUGH DIGGING EASTWARD INTO THE YELLOW SEA IS POISED TO WEAKEN THE STR. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE LAST PROGNOSTIC REASONING BULLETIN. B. TD 20W IS EXPECTED TO TRACK ALONG THE PERIMETER OF THE STR. THE AFOREMENTIONED TROUGH WILL WEAKEN THE STEERING RIDGE AND CAUSE THE TD TO RECURVE NORTHEASTWARD AFTER TAU 48. THE SYSTEM WILL GRADUALLY INTENSIFY AS UPPER LEVEL CONDITIONS REMAIN FAVORABLE, PEAKING AT TAU 72 DUE TO INCREASED OUTFLOW DURING ITS INITIAL EXPOSURE TO THE STRONG WESTERLIES AHEAD OF THE TROUGH. THE NUMERICAL GUIDANCE MODELS ARE SPLIT WITH JGSM, NOGAPS, AND GFDN DEVIATING TOWARDS THE SOUTHWEST AT THE RECURVATURE POINT. THERE IS LOW CONFIDENCE IN THE INITIAL 72 HOURS OF THE FORECAST GIVEN THE EXTREME TRACK SOLUTIONS AND THE POSSIBILITY OF A LLCC REFORMATION. C. AFTER TAU 72, TD 20W IS EXPECTED TO ACCELERATE NORTHEASTWARD AND BECOME EXTRA-TROPICAL BY END OF FORECAST. THE SYSTEM WILL RAPIDLY WEAKEN AS VWS INCREASES AND SEA SURFACE TEMPERATURES DECREASE. THERE IS ALSO LOW CONFIDENCE IN THE EXTENDED PORTION OF THE FORECAST MAINLY DUE TO DIFFERENCES IN LATERAL SPEED IN THE MODEL GUIDANCE. // NNNN NNNN