WDPN31 PGTW 081500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 19W (VONGFONG) WARNING NR 24// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUPER TYPHOON (STY) 19W (VONGFONG), LOCATED APPROXIMATELY 510 NM SOUTH-SOUTHEAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A FAIRLY SYMMETRIC ANNULUS OF DEEP CONVECTION SURROUNDING A ROUND 23-NM EYE. A 081234Z AMSU-B IMAGE INDICATES DEEP CONVECTIVE BANDING WRAPPING INTO THE SYSTEM. BASED ON THE ROUND EYE, THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION AND RECENT MOTION. THE INITIAL INTENSITY IS ASSESSED AT 145 KNOTS BASED ON DVORAK INTENSITY ESTIMATES RANGING FROM T7.0 TO T7.5 (140 TO 155 KNOTS). UPPER-LEVEL ANALYSIS CONTINUES TO INDICATE EXCELLENT RADIAL OUTFLOW, ENHANCED BY A TUTT CELL TO THE EAST. STY 19W IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF THE SUBTROPICAL RIDGE (STR). THE 08/00Z 500MB ANALYSIS DEPICTS A BREAK IN THE STR OVER OKINAWA WITH ZONAL WESTERLY MIDLATITUDE FLOW POLEWARD OF THE STR. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. STY 19W IS FORECAST TO TURN INCREASINGLY POLEWARD WITHIN THE NEXT 12 HOURS AS IT ROUNDS THE SOUTHWEST PERIPHERY OF THE STR AND TRACKS ALONG THE WESTERN PERIPHERY OF THE STR TOWARD THE AFOREMENTIONED WEAKNESS POSITIONED NEAR OKINAWA. AFTER TAU 24, UNCERTAINTY INCREASES DUE TO SIGNIFICANT MODEL DIFFERENCES IN THE STRENGTH OF A MIDLATITUDE SHORTWAVE TROUGH FORECAST TO DIG OVER WESTERN JAPAN AFTER TAU 36. THE JGSM, JENS AND ECMWF TRACKERS INDICATE A MORE NORTH-NORTHEASTWARD TRACK THROUGH TAU 72, AFFECTED MORE BY THE TROUGH, WHILE GFS, HWRF AND COAMPS-TC INDICATE A MORE NORTH-NORTHWESTWARD TRACK TOWARD OKINAWA THAT REFLECTS NO INTERACTION WITH THE TROUGH. THE REMAINDER OF THE GUIDANCE INDICATES A GENERALLY NORTHWARD TRACK THROUGH TAU 72. ENSEMBLE GUIDANCE ALSO INDICATES UNCERTAINTY THROUGH THIS PERIOD, REFLECTING THE COMPLEX STEERING ENVIRONMENT AND VARYING DEGREES OF MIDLATITUDE TROUGH INTERACTION. THE JTWC FORECAST TRACK REMAINS CONSISTENT WITH PREVIOUS FORECASTS AND IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS. STY 19W IS FORECAST TO MAINTAIN STY STRENGTH THROUGH TAU 36 BUT IS FORECAST TO GRADUALLY WEAKEN THROUGH TAU 72. C. IN THE EXTENDED PERIOD, HIGH UNCERTAINTY REMAINS AS A MIDLATITUDE SHORTWAVE RIDGE PROPAGATES NORTH OF THE SYSTEM AND RE- BUILDS THE STR TO VARYING DEGREES. MODEL SOLUTIONS SHOW A WIDE SPREAD OF SOLUTIONS IN A GENERALLY NORTH-NORTHWESTWARD ORIENTATION. NEAR TAU 96, STY 19W IS FORECAST TO RE-CURVE NORTHEASTWARD AS IT BEGINS TO INTERACT WITH THE MIDLATITUDE WESTERLIES AND BEGIN EXTRA- TROPICAL TRANSITION. INCREASING VERTICAL WIND SHEAR NORTH OF 28N LATITUDE WILL SERVE TO WEAKEN THE SYSTEM. OVERALL, THERE IS LOW CONFIDENCE IN THE FORECAST TRACK DUE TO THE LARGE MODEL SPREAD.// NNNN