WDPN34 PGTW 230300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (FOURTEEN) WARNING NR 06// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 14W (FOURTEEN), LOCATED APPROXIMATELY 310 NM EAST OF MINAMI TORI SHIMA, HAS TRACKED NORTH-NORTHEASTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTI-SPECTRAL SATELLITE IMAGERY (MSI) SHOWS A FULLY EXPOSED AND ELONGATED LOW LEVEL CIRCULATION CENTER (LLCC) WITH A LARGE AREA OF CONVECTION IN THE NORTHEASTERN QUADRANT. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC EVIDENT IN THE MSI LOOP. THE INITIAL INTENSITY OF 40 KNOTS IS HEDGED ABOVE A PGTW DVORAK CURRENT INTENSITY ESTIMATE OF T2.5 (35 KNOTS) BASED ON THE VAST CONVECTIVE STRUCTURE AND A 222218Z OSCAT IMAGE WITH A SMALL REGION OF 40 KNOT WIND BARBS EAST OF THE LLCC. UPPER LEVEL ANALYSIS SHOWS THAT TS 14W HAS A ROBUST POLEWARD OUTFLOW CHANNEL WHICH IS ENHANCED BY A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL THAT IS LOCATED DUE EAST OF THE LLCC. ENVIRONMENTAL ANALYSIS SHOWS THAT THE SYSTEM IS IN AN AREA OF LOW (10-15 KNOTS) SOUTHWESTERLY VERTICAL WIND SHEAR (VWS) WHICH HAS DECREASED SIGNIFICANTLY OVER THE LAST 6 HOURS AS THE SYSTEM MOVES AWAY FROM ANOTHER TUTT CELL THAT IS LOCATED TO THE WEST OF THE LLCC. THE TUTT TO THE WEST IS PRODUCING THE SOUTHWESTERLY VWS THAT IS RESPONSIBLE FOR THE ABSENCE OF CONVECTION IN THE WESTERN SEMI-CIRCLE AND CAUSING THE SYSTEM TO EXHIBIT SUBTROPICAL CHARACTERISTICS LIKE THE EXPANSIVE ASYMMETRIC WIND FIELD. SEA SURFACE TEMPERATURES IN THE AREA REMAIN WARM (27-28 CELSIUS) AND FAVORABLE FOR ADDITIONAL INTENSIFICATION. TS 14W IS TRACKING NORTH ALONG THE SOUTHWESTERN EXTENT OF AN EXTENSION OF A SUB-TROPICAL RIDGE (STR) LOCATED TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 14W IS FORECAST TO INITIALLY TRACK NORTH THROUGH TAU 24 AT WHICH TIME THE TRACK BEGINS TO SHIFT NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR TO THE NORTHEAST. THE SYSTEM IS FORECAST TO GRADUALLY INTENSIFY AS IT MOVES NORTH OF THE TUTT CELL TO THE WEST, CAUSING VWS TO DECREASE. ALONG TRACK SEA SURFACE TEMPERATURES REMAIN MARGINALLY FAVORABLE (26-27 CELSIUS) AND 14W IS EXPECTED TO MAINTAIN GOOD OUTFLOW THROUGH TAU 48. THE GRADUAL INTENSIFICATION WILL CONTINUE UNTIL THE SYSTEM REACHES A PEAK OF 60 KNOTS AROUND TAU 48. AFTER TAU 48, THE SYSTEM WILL BEGIN A STEADY WEAKENING TREND, THE RESULT OF INCREASING VERTICAL WIND SHEAR DUE TO AN APPROACHING MID-LATITUDE TROUGH. ADDITIONALLY, AROUND TAU 60, THE SYSTEM WILL BE NORTH OF 35 DEGREES LATITUDE, WHERE SEA SURFACE TEMPERATURES BECOME UNFAVORABLE (< 26 CELSIUS) WHICH WILL CONTRIBUTE TO THE WEAKENING TREND. THE SYSTEM IS FORECAST TO BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU 48 AND COMPLETE ETT BY TAU 72. DYNAMIC MODEL GUIDANCE IS IN STRONG AGREEMENT THROUGH TAU 72, HOWEVER, OVER THE LAST 6 HOURS THE SYSTEM HAS TRACKED NORTHEASTWARD WHILE THE FORECAST CALLED FOR A DUE NORTH TRACK. EARLIER FORECASTS HAD PREDICTED VARIATIONS IN DIRECTION BUT RECENT MODEL RUNS HAVE ELIMINATED THOSE FEATURES. THE MODEL GUIDANCE HAS ALSO SIGNIFICANTLY ACCELERATED THE ETT AS THE APPROACHING TROUGH BEGINS TO IMPACT THE SYSTEM EARLIER THAN ORIGINALLY FORECAST. DUE TO THE DISAGREEMENT BETWEEN THE TRACK AND THE FORECASTED TRACK BASED ON MODEL GUIDANCE, AND THE RAPID CHANGES IN THE TIMELINE FOR ETT, THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN