MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (MALAKAS) WARNING NR 36// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 18W (MALAKAS), LOCATED APPROXIMATELY 49 NM WEST OF YOKOSUKA, JAPAN, HAS TRACKED EAST-NORTHEASTWARD AT 24 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AND RADAR IMAGERY DEPICT A BROAD, ILL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH DEEP CONVECTION SHEARED TO THE NORTHEAST DUE TO STRONG (50 TO 60 KNOTS) WESTERLY VERTICAL WIND SHEAR (VWS). BOTH EIR AND RADAR IMAGERY SUGGEST A WEAK FRONTAL STRUCTURE, HOWEVER, TS 18W IS CLEARLY WEAKENING RAPIDLY AS IT CROSSES HONSHU SO THE SYSTEM IS UNLIKELY TO DEVELOP INTO AN EXTRA- TROPICAL LOW. SURFACE OBSERVATIONS ACROSS CENTRAL HONSHU GENERALLY INDICATE SUSTAINED WINDS LESS THAN 20 KNOTS WITH NO DEFINED CIRCULATION EVIDENT. A 201145Z METOP-A 89GHZ IMAGE DEPICTS SHALLOW CURVED BANDING OVER THE SOUTH QUADRANT (OVER WATER) OF THE LLCC BUT NO CONVECTIVE STRUCTURE ELSEWHERE. DUE TO THE WEAK NATURE OF THE LLCC, THERE IS LOW CONFIDENCE IN THE CURRENT POSITION. THE CURRENT INTENSITY IS DIFFICULT TO ACCURATELY ASSESS OVER THE ROUGH TERRAIN, HOWEVER, IT IS CONSERVATIVELY ESTIMATED AT 40 KNOTS BUT COULD BE LOWER. CURRENTLY TS 18W IS ACCELERATING NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE, WITHIN THE MIDLATITUDE WESTERLIES. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 18W IS FORECAST TO TRACK RAPIDLY NORTHEASTWARD TO EAST- NORTHEASTWARD THROUGH THE FORECAST PERIOD. DYNAMIC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. THE SYSTEM WILL CONTINUE TO WEAKEN RAPIDLY DUE TO LAND INTERACTION, PERSISTENT STRONG VWS AND COOLER SST, AND IS EXPECTED TO DISSIPATE BY TAU 24.// NNNN NNNN