MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 04W (MAYSAK) WARNING NR 28// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 04W (MAYSAK), LOCATED APPROXIMATELY 636 NM EAST OF MANILA, PHILIPPINES HAS TRACKED NORTHWESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A WEAKENING CONVECTIVE CORE STRUCTURE THAT IS SHEARING NORTHEASTWARD DUE TO ENCOUNTERING HIGH (30 KNOT) SOUTHWESTERLY VERTICAL WIND SHEAR (VWS) ASSOCIATED WITH A MID-LATITUDE TROUGH TO THE WEST. A 021808Z SSMI 89GHZ MICROWAVE IMAGE CONTINUES TO SHOW A MICROWAVE EYE FEATURE, HOWEVER, ALL OF THE CONVECTION IS DISPLACED TO THE NORTHEAST WITH DRY AIR WRAPPING AROUND THE SOUTHERN PERIPHERY FROM THE WEST. UPPER LEVEL ANALYSIS INDICATES SIGNIFICANT DRY AIR BEING ADVECTED INTO THE PHILIPPINE SEA BY THE AFOREMENTIONED TROUGH. THESE FACTORS ARE OFFSETTING THE VIGOROUS POLEWARD OUTFLOW EVIDENT ON THE WATER VAPOR LOOP. THE INITIAL POSITION IS BASED ON THE MICROWAVE EYE FEATURE WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS HEDGED SLIGHTLY LOWER THAN DVORAK CURRENT INTENSITY ESTIMATES OF T5.5 (105 KNOTS) TO REFLECT THE SYSTEM'S WEAKENING STRUCTURE. TY MAYSAK IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF THE DEEP LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 04W WILL CONTINUE TRACKING NORTHWESTWARD THROUGH TAU 24 UNDER THE INFLUENCE OF THE STEERING STR. BETWEEN TAU 24 AND 36, TY MAYSAK WILL TURN SLIGHTLY WESTWARD AS THE SHORTWAVE TROUGH PROPAGATES EAST AND AN EXTENSION OF THE STEERING STR BUILDS IN NORTH OF THE SYSTEM. BEYOND TAU 36, THE SYSTEM WILL TRACK NORTHWESTWARD AGAIN AS THE STR REORIENTS TO ITS ORIGINAL POSITION TO THE NORTHEAST. UPPER LEVEL ENVIRONMENTAL CONDITIONS WILL CONTINUE TO DETERIORATE AS VWS INCREASES THROUGH TAU 36 AND UPPER LEVEL DIVERGENCE DECREASES. AS THE UPPER LEVEL TROUGH MOVES OUT OF THE REGION VWS WILL DROP BACK TO MARGINAL LEVELS, CAUSING A SLOWER WEAKENING JUST PRIOR TO LANDFALL. BEYOND TAU 48, THE WEAKENING WILL BE ENHANCED DUE TO FRICTIONAL EFFECTS AS THE SYSTEM MAKES LANDFALL OVER CENTRAL LUZON. AS TY 04W RE-EMERGES BACK OVER WATER IN THE SOUTH CHINA SEA, IT WILL CONTINUE WEAKENING DUE TO HIGH VWS AND WEAK DIVERGENCE ALOFT. C. IN THE EXTENDED TAUS, TY MAYSAK WILL FURTHER WEAKEN DUE TO THE POOR ENVIRONMENTAL CONDITIONS. NEAR TAU 120, A STRONG NORTHEASTERLY SURGE THROUGH THE TAIWAN STRAIT WILL FORCE THE WEAKENED SYSTEM TO BEND WESTWARD. IN ADDITION TO A POOR UPPER LEVEL ENVIRONMENT, TY 04W WILL ALSO ENCOUNTER SST BELOW 26 CELSIUS. OVERALL, DYNAMIC GUIDANCE REMAINS IN GOOD AGREEMENT, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.// NNNN NNNN