MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (TWENTYTHREE) WARNING NR 01// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 23W (TWENTYTHREE), LOCATED APPROXIMATELY 866 NM EAST-SOUTHEAST OF IWO TO, HAS TRACKED WEST-NORTHWESTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND A 080202Z AMSR2 IMAGE DEPICTS AN AREA OF IMPROVING CONSOLIDATION WITH FORMATIVE BANDING ON THE NORTH AND WESTERN PERIPHERIES WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER GIVING HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY IS ASSESSED AT 25 KNOTS AND IS BASED ON THE IMPROVED CONVECTIVE STRUCTURE AND DVORAK ESTIMATES RANGING FROM T1.5 TO T2.0 (25 TO 30 KNOTS). UPPER-LEVEL ANALYSIS SHOWS IMPROVING POLEWARD OUTFLOW, BUT THE PRESENCE OF A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) TO THE SOUTHWEST IS IMPINGING ON EQUATORWARD OUTFLOW AND ESTABLISHMENT OF DEEP CONVECTION ON THE SOUTHERN PERIPHERY. VERTICAL WIND SHEAR IS FAVORABLE AT 10 TO 15 KNOTS, AND SEA SURFACE TEMPERATURES ARE NEAR 29 CELSIUS. CURRENTLY TD 23W IS TRACKING WEST-NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE. 3. FORECAST REASONING. A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE FORECAST PHILOSOPHY. B. TD 23W WILL CONTINUE ON A TRACK NORTHWEST ALONG THE CURRENT STEERING RIDGE. THE SOUTHERN POSITIONED TUTT WILL CONTINUE TO INFLUENCE THE SYSTEM FOR THE NEXT 24 TO 36 HOURS, HOWEVER, UPPER- LEVEL CONDITIONS ARE EXPECTED TO IMPROVE AS THE TUTT EVENTUALLY MOVES OFF TO THE SOUTHWEST. FOR THIS REASON GRADUAL INTENSIFICATION IS EXPECTED THROUGH TAU 48. BETWEEN TAU 48 AND 72, TD 23W WILL SLOW AS IT ROUNDS THE RIDGE AXIS AND BEGINS TO TAP INTO THE WESTERLY JET TO THE NORTH. THE PEAK INTENSITY IS EXPECTED TO REACH 75 KNOTS DURING THIS TIME. C. IN THE EXTENDED FORECAST PERIOD, TD 23W WILL TURN TO THE NORTHEAST AFTER ROUNDING THE STEERING RIDGE AXIS. THE SYSTEM WILL ACCELERATE AND EXPERIENCE HIGHER WIND SHEAR VALUES AS IT APPROACHES THE STRONG WESTERLY FLOW. BY TAU 120 TD 23W WILL BEGIN EXTRATROPICAL TRANSITION AS IT INTERACTS WITH THE BAROCLINIC ZONE. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THE FORECAST PHILOSOPHY DIFFERING SLIGHTLY IN THE EXACT POSITION AND TIMING IN THE TURN TO THE NORTHWEST, LENDING HIGH CONFIDENCE TO THE FORECAST TRACK.// NNNN NNNN