MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (KROVANH) WARNING NR 06// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 20W (KROVANH), LOCATED APPROXIMATELY 165 NM EAST- NORTHEAST OF PAGAN, HAS TRACKED NORTHWESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A 152151Z GMI IMAGE AND A 152332Z PGTW SATELLITE FIX. THE INTENSITY OF 45 KNOTS IS CONSISTENT WITH SUBJECTIVE DVORAK AND AUTOMATED SATELLITE INTENSITY ESTIMATES FROM MULTIPLE REPORTING AGENCIES. RECENT ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS INCREASING ORGANIZATION, WITH DEEP CONVECTIVE BANDING WRAPPING DIRECTLY INTO THE SYSTEM CENTER. VERTICAL WIND SHEAR HAS DECREASED AS THE SYSTEM SHIFTED CLOSER TO AN UPPER-LEVEL RIDGE AXIS DURING THE PAST SIX HOURS. TS 20W CONTINUES TO TRACK ALONG THE PERIPHERY OF A SUBTROPICAL STEERING RIDGE TO THE NORTH. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 20W IS EXPECTED TO TRACK GENERALLY NORTHWESTWARD ALONG THE PERIPHERY OF THE CURRENT STEERING RIDGE FOR THE NEXT 36 HOURS BEFORE TURNING POLEWARD AND ROUNDING THE RIDGE AXIS THROUGH TAU 72. STEADY INTENSIFICATION IS EXPECTED AS SYSTEM TRACKS OVER VERY WARM WATER, VERTICAL WIND SHEAR DECREASES, AND POLEWARD OUTFLOW IMPROVES. INTENSITY IS EXPECTED TO PEAK AROUND 105 KNOTS BETWEEN TAU 48 AND TAU 72. HOWEVER, A PERIOD OF RAPID INTENSIFICATION AND HIGHER MAXIMUM INTENSITY ARE POSSIBLE GIVEN FAVORABLE ENVIRONMENTAL CONDITIONS. C. TS 20W IS EXPECTED TO ACCELERATE INTO THE MIDLATITUDE BAROCLINIC ZONE AND BECOME EXTRATROPICAL IN THE EXTENDED FORECAST PERIOD. INCREASING WESTERLY VERTICAL WIND SHEAR AND PASSAGE OVER COOLER WATER WILL INDUCE SOME WEAKENING DURING THE TRANSITION. DYNAMIC MODEL TRACK FORECASTS REMAIN IN FAIR AGREEMENT. SOME ENSEMBLE GUIDANCE STILL TRACKS THE SYSTEM FARTHER TO THE WEST BEFORE RECURVATURE, BUT THE JAPANESE ENSEMBLE MEAN HAS MOVED CLOSER TO THE DETERMINISTIC GROUPING IN THE LATEST MODEL RUN. HWRF, ON THE OTHER SIDE OF THE GUIDANCE ENVELOPE, DEPICTS A TIGHTER RECURVATURE THAN THE PRIMARY GROUPING. THE CURRENT OFFICIAL FORECAST LIES CLOSE TO THE MULTI-MODEL CONSENSUS. GIVEN NOTED UNCERTAINTY IN ORIENTATION OF THE RECURVATURE, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST.// NNNN NNNN