MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (YUTU) WARNING NR 44// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 31W (YUTU), LOCATED APPROXIMATELY 180 NM SOUTHEAST OF HONG KONG, HAS TRACKED NORTH-NORTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS DEEP CONVECTION BECOMING MORE RAGGED AND DISORGANIZED AROUND AN ILL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE, FOLLOWING THE REGION OF MAXIMUM CONVECTIVE CURVATURE IN THE 010552Z ATMS 88.2GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS ASSESSED AT 45 KNOTS, BASED ON DVORAK ESTIMATES OF T3.0 FROM PGTW, RJTD, AND RCTP. THE SYSTEM IS CURRENTLY EXPERIENCING MODERATE VERTICAL WIND SHEAR (15 TO 25 KNOTS), WITH GOOD POLEWARD OUTFLOW BUT RESTRICTED ELSEWHERE. SEA SURFACE TEMPERATURES ARE ONLY MARGINAL FOR DEVELOPMENT (26 DEGREES CELSIUS). TS 31W CONTINUES TO TRACK TOWARD THE NORTH-NORTHWEST AROUND A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE EAST. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 31W IS FORECAST TO CONTINUE ON A NORTH-NORTHWESTWARD TRACK. AS IT INTERACTS WITH STRONG MID-LATITUDE WESTERLIES, VERTICAL WIND SHEAR IS EXPECTED TO DRAMATICALLY INCREASE. TOGETHER WITH COOLER SEA SURFACE TEMPERATURES, TS 31W IS EXPECTED TO DISSIPATE OVER WATER AROUND TAU 36. DYNAMIC MODEL GUIDANCE GREATLY DIVERGES IN A CLASSIC SQUASHED SPIDER PATTERN, GIVEN THAT THE LLCC OF TS 31W IS EXPECTED TO DECOUPLE UNDER THE INFLUENCE OF STRONG MID-LATITUDE DYNAMICS. THE OFFICIAL FORECAST TRACK CALLS FOR A SLOWING IN FORWARD MOTION THROUGH DISSIPATION. THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN