MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE) WARNING NR 02// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 21W (TWENTYONE) LOCATED APPROXIMATELY 297 NM NORTHWEST OF NAVSTA GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MSI SHOWS PERSISTENT SYMMETRICAL DEEP CONVECTION AND A LOW LEVER SPINNER TO THE EAST. A 212141Z SSMIS 37 GHZ IMAGE SHOWS SOME CURVATURE IN THE LOW LEVELS NEAR THE BEST TRACK, GIVING SOME, ALBEIT VERY SLIGHT, CONFIDENCE IN THE OVERALL POSITION OF THE SYSTEM DUE TO THE MULTIPLE VORTICES PRESENT. THE INITIAL INTENSITY IS HELD AT 25 KNOTS AS DT ESTIMATES RANGE FROM 1.0 TO 1.5. UPPER LEVEL ANALYSIS INDICATES 15 TO 25 KNOTS OF EASTERLY VWS OFFSET BY GOOD DIVERGENCE ALOFT. THE SYSTEM IS CURRENTLY TRACKING ON THE SOUTHERN SIDE OF A STR TO THE NORTH. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 21W WILL TRACK TO THE WEST-NORTHWEST UNDER THE INFLUENCE OF THE STR THROUGH TAU 36 WITH MARGINAL INTENSIFICATION. EXPECT A MORE POLEWARD TREND IN THE TRACK AS A MID-LATITUDE SHORTWAVE TROUGH WILL CREATE A SMALL BREAK IN THE STR. EXPECT CONTINUED INTENSIFICATION OF THE SYSTEM AS OUTFLOW IMPROVES BY TAU 48 THROUGH THE END OF THE FORECAST PERIOD, EXCEEDING TYPHOON STRENGTH BY TAU 72. C. IN THE EXTENDED FORECAST, TD 21W WILL CONTINUE TO INTENSIFY AS POLEWARD OUTFLOW IMPROVES AND OHC REMAINS CONDUCIVE. THE SYSTEM WILL CONTINUE TO TRACK POLEWARD THROUGH THE BREAK IN THE RIDGE. DYNAMIC MODEL GUIDANCE REMAINS FAIRLY SPREAD DUE TO THE SIGNIFICANCE AND TIMING OF THE BREAK IN THE RIDGE. THERE REMAINS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN