MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 20W (HAGIBIS) WARNING NR 011// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUPER TYPHOON (STY) 20W (HAGIBIS), LOCATED APPROXIMATELY 168 NM NORTH OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 17 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) DEPICTS STY 20W AS A HIGHLY SYMMETRIC SYSTEM WITH SPIRAL CONVECTIVE BANDS WRAPPING TIGHTLY INTO A SMALL, 6 NM DIAMETER EYE SURROUNDED BY A WELL-DEFINED EYEWALL. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION. THE INITIAL INTENSITY IS SET AT 140 KTS, SUPPORTED BY DVORAK CURRENT INTENSITY (CI) ESTIMATES OF T7.0/140 KTS FROM PGTW AND RJTD, BOTH OF WHICH ARE CORROBORATED BY THE CIMSS ADVANCED DVORAK TECHNIQUE (ADT) AND SATCON ESTIMATES. THERE ARE INDICATIONS THAT THE SYSTEM HAS BEEN UNDERGOING AN EYEWALL REPLACEMENT CYCLE (ERC) SINCE THE PREVIOUS WARNING, RESULTING IN A STEADY-STATE INTENSITY OF 140 KTS. UPPER-LEVEL ANALYSIS SHOWS STRONG RADIAL OUTFLOW WITH ENHANCED OUTFLOW EQUATORWARD AND EASTWARD. WITH LOW (05-10 KTS) VERTICAL WIND SHEAR (VWS) AND HIGH (30-31 CELSIUS) SEA SURFACE TEMPERATURES (SST), STY 20W CONTINUES TO TRACK THROUGH A HIGHLY FAVORABLE ENVIRONMENT, WITH SOME FURTHER INTENSIFICATION POSSIBLE AFTER THE COMPLETION OF THE CURRENT ERC. A SUBTROPICAL RIDGE (STR) TO THE NORTH IS THE PRIMARY STEERING INFLUENCE AS THE SYSTEM TRACKS WEST-NORTHWESTWARD ALONG ITS SOUTHERN PERIPHERY. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE LAST PROGNOSTIC REASONING MESSAGE. B. THROUGH TAU 72, STY 20W WILL CONTINUE TO TRACK NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE AFOREMENTIONED STR. THE FAVORABLE ENVIRONMENT (LOW VWS, HIGH SST, AND EXCELLENT UPPER-LEVEL OUTFLOW) IS EXPECTED TO PERSIST THROUGH THE SHORT-TERM FORECAST PERIOD, ALLOWING FOR INTENSIFICATION TO A PEAK OF 145 KTS BY TAU 12. AFTERWARDS, THE INTENSITY WILL SLOWLY BEGIN TO WEAKEN AS THE SYSTEM?S OUTFLOW BEGINS TO BE DISRUPTED TO THE NORTHWEST. NUMERICAL MODELS ARE IN TIGHT AGREEMENT, SLOWLY INCREASING TO A CROSS-TRACK SPREAD OF 140 NM BY TAU 72, LENDING HIGH CONFIDENCE IN THIS PORTION OF THE JTWC TRACK FORECAST. C. IN THE EXTENDED FORECAST, A SHORTWAVE TROUGH OVER JAPAN IS EXPECTED TO DEEPEN, ERODING THE STR AND ALLOWING STY 20W TO TURN NORTHWARD AS IT ROUNDS THE STR AXIS. AROUND TAU 96, THE SYSTEM WILL BEGIN TO RECURVE, TRACKING NORTHEASTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD. AS IT DOES SO, THE SYSTEM WILL SLOWLY WEAKEN IN RESPONSE TO INCREASE VWS ASSOCIATED WITH THE APPROACHING TROUGH, WHICH WILL OFFSET THE OTHERWISE FAVORABLE ENVIRONMENT. THE NUMERICAL MODELS HAVE A LOW (90 NM) CROSS-TRACK SPREAD AT TAU 120. HOWEVER, THE TIMING OF THE RECURVATURE RESULTS IN UNCERTAINTIES WITH THE FORWARD MOTION OF THE SYSTEM, LENDING LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST.// NNNN NNNN