MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (LIONROCK) WARNING NR 28// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 12W (LIONROCK), LOCATED APPROXIMATELY 250 NM SOUTHEAST OF KADENA AB, HAS TRACKED SOUTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS DEEP CONVECTION ASSOCIATED WITH TY 12 WRAPPING TIGHTLY AROUND A PARTIALLY CLOUD-FILLED EYE. THE CONVECTIVE SIGNATURE IS SLIGHTLY ASYMMETRIC WITH A TIGHTER BRIGHTNESS TEMPERATURE GRADIENT IN THE NORTHEAST QUADRANT, IMPLYING THE PRESENCE OF SOME NORTHEASTERLY VERTICAL WIND SHEAR. A 241839Z AMSU 89GHZ MICROWAVE IMAGE LIKEWISE DEPICTS THE DEEPEST CONVECTION LOCATED JUST SLIGHTLY DOWNSHEAR OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE SIZE OF TY 12W REMAINS RELATIVELY COMPACT, WITH MODEST RADIAL OUTFLOW NEAR THE LLCC MAINTAINING THE INTENSITY OF THE SYSTEM. FURTHER AWAY FROM TY 12W, OUTFLOW IS RESTRICTED TO THE NORTH, DUE TO THE PRESENCE OF AN EASTWARD EXTENSION OF A SUBTROPICAL RIDGE (STR) OVER CHINA. HOWEVER, THAT EFFECT HAS RECENTLY RELAXED, LIKELY CONTRIBUTING TO THE RECENT INTENSIFICATION PHASE OF TY 12W. THE CURRENT INTENSITY IS ASSESSED AT 110 KNOTS BASED ON A BLEND OF DVORAK ESTIMATES FROM T6.0 (PGTW) AND T5.5 (KNES AND RJTD). THE SYSTEM CONTINUES TRACKING TOWARD THE SOUTHWEST AS IT IS STEERED BY THE STR. 3. FORECAST REASONING. A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE, EXCEPT THE INTENSITY FORECAST AT THE EXTENDED RANGE HAS BEEN REDUCED GIVEN THE LATEST NUMERICAL MODEL GUIDANCE. B. TY 12W WILL CONTINUE MOVING TOWARD THE SOUTHWEST WITH A SLOWING IN FORWARD MOTION EXPECTED AS IT ENTERS A REGION OF WEAK STEERING. QUASISTATIONARY MOTION IS EXPECTED FROM TAU 12 TO 24, FOLLOWED BY A TURN TOWARD THE NORTHEAST. ALL NUMERICAL MODEL GUIDANCE INDICATE THIS EVENTUAL TURN, WITH DIFFERENCES IN WHETHER THE TURN WILL OCCUR TO THE NORTH OR TO THE SOUTH OF THE CURRENT TRACK. WARM WATER AND CONTINUED LOW TO MODERATE VERTICAL WIND SHEAR SHOULD ALLOW TY 12W TO MAINTAIN ITS INTENSITY, WITH FLUCTUATIONS EXPECTED GIVEN THE COMPACT NATURE OF THE SYSTEM. SOME GRADUAL WEAKENING IS EXPECTED AFTER COOLER WATER IS UPWELLED, ESPECIALLY FROM TAU 12 TO 24. C. IN THE EXTENDED TAUS, A DEEP MID-LATITUDE TROUGH DEEPENS OVER JAPAN, WITH A DOUBLE JETSTREAK PATTERN ASSOCIATED WITH CYCLOGENESIS IN THE SEA OF JAPAN, WHICH WILL COMPLICATE BOTH THE TRACK AND INTENSITY FORECAST OF TY 12W. ALTHOUGH A TRACK TOWARD THE NORTHEAST IS EXPECTED, THERE IS SIGNIFICANT UNCERTAINTY WITH REGARD TO WHETHER THE TRACK WILL TURN NORTHWARD INTO JAPAN AS SUGGESTED BY THE ECMWF OR STAY FURTHER TO THE SOUTH AS INDICATED BY THE GFS, UKMET, AND OTHER TRACKERS IN THE MODEL SUITE. GIVEN THE INTENSITY OF THE MERIDIONAL FLOW PATTERN ASSOCIATED WITH THE MID-LATITUDE SYSTEM THAT IS FORECAST TO DEVELOP NEAR AND TO THE WEST OF JAPAN, IT IS LIKELY THAT TY 12W WILL INTERACT WITH THE BAROCLINIC ZONE AND BEGIN EXTRATROPICAL TRANSITION AT LOWER LATITUDE THAN TYPICAL TROPICAL CYCLONES IN THIS REGION. HOWEVER, A MORE SOUTHERN TRACK WOULD ALLOW IT TO MAINTAIN A HIGHER MAXIMUM SUSTAINED WIND SPEED. THE CURRENT INTENSITY FORECAST ASSUMES AN INTERACTION THAT WOULD LEAD TO GREATER WIND SHEAR AND A DISRUPTION OF THE INNER CORE CONVECTION. HOWEVER, GIVEN THE COMPLEXITY OF THE STEERING ENVIRONMENT AND UNCERTAINTY IN BOTH THE NEAR-TERM QUASISTATIONARY PERIOD AND THE SUBSEQUENT ACCELERATION TO THE NORTHEAST, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK AND INTENSITY.// NNNN NNNN