WDPN31 PGTW 192100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (RAI) WARNING NR 028// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.0N 110.6E INITIAL INTENSITY: 90 KTS GEOGRAPHIC REFERENCE: 133 NM EAST OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: NORTHWARD AT 12 KTS SIGNIFICANT WAVE HEIGHT: 26 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TYPHOON 28W CONTINUES TO STEADILY AND RAPIDLY WEAKEN. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAPIDLY DETERIORATING SYSTEM, WITH WARMING CLOUD TOPS, AND A LACK OF ORGANIZED DEEP CONVECTION. THE RAGGED EYE THAT WAS PRESENT EVEN JUST A FEW HOURS AGO HAS COMPLETELY DEGRADED AND DISAPPEARED BY THE 1900Z HOUR. A 191635Z GPM COLORIZED 37GHZ MICROWAVE IMAGE SHOWED THAT WHILE THE UPPER-LEVELS HAVE BEEN SHEARED AWAY TO THE NORTH, THE LOW LEVEL CIRCULATION CENTER (LLCC) REMAINS WELL DEFINED, LAGGING A BIT BEHIND THE UPPER-LEVEL FEATURES DUE TO THE STRONG SOUTHERLY SHEAR. THE BULK OF MODERATE CONVECTION IS CONFINED TO THE NORTHWEST SIDE OF THE LLCC IN THE MICROWAVE IMAGERY, WITH LITTLE TO NO CONVECTIVE ACTIVITY TO THE EAST. THE INITIAL POSITION IS THUS PLACED WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION OF THE LLCC IN THE PREVIOUSLY MENTIONED MICROWAVE IMAGERY. INTENSITY ESTIMATES ARE STRUGGLING TO KEEP UP WITH THE RATE OF WEAKENING, AND THUS ARE A BIT HIGH. AGENCY CURRENT INTENSITY ESTIMATES RANGE BETWEEN T4.0 TO T6.0, WHILE THE ADT WAS AT T5.4. HOWEVER, SATCON AT 90 KNOTS AND THE NEW AIDT AT 83 KNOTS SEEMED A BIT MORE REALISTIC. HENCE THE INITIAL INTENSITY IS ASSESSED AT 90 KNOTS, WITH AN OVERALL LOW CONFIDENCE DUE TO RAPID WEAKENING TREND. ANALYSIS REVEALS STRONG SOUTHERLY FLOW OVER TOP OF THE SYSTEM, FLOWING INTO A ROBUST POLEWARD OUTFLOW INTO THE UPPER-LEVEL WESTERLIES. CIMSS ASSESSMENT OF VWS REMAINS RELATIVELY LOW (10-15 KTS), THOUGH HWRF MODEL SOUNDINGS SUGGEST MUCH HIGHER SHEAR VALUES NEAR 30 KNOTS. THE TRUE SHEAR VALUES LIKELY ARE IN THE MIDDLE, NEAR 15-20 KNOTS. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: TY 28W IS IN THE PROCESS OF ROUNDING THE AXIS OF A DEEP SUBTROPICAL RIDGE (STR), CENTERED TO THE NORTHEAST OF LUZON. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.0 - 65 KTS RJTD: T6.0 - 115 KTS KNES: T5.5 - 102 KTS CIMSS SATCON: 89 KTS AT 191331Z CIMSS ADT: 99 KTS AT 191740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE VWS: 15-20 KTS SST: 25-26 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: LOW INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. HOWEVER THE FORECAST HAS BEEN TRUNCATED TO 72 HOURS. FORECAST DISCUSSION: TY 28W IS MOVING NORTHWARD, ROUNDING THE AXIS OF THE STR TO THE EAST. THE SYSTEM IS FORECAST TO GRADUALLY TURN NORTHEASTWARD ALONG THE GRADIENT BETWEEN THE NORTHWEST SIDE OF THE STR AND A MID-LATITUDE TROUGH TO THE WEST. AS THE SYSTEM WEAKENS TO TD STRENGTH IT WILL TURN EAST OR EVEN SOUTHEAST TOWARDS THE END OF THE FORECAST, UNDER THE INFLUENCE OF THE LOW LEVEL FLOW PATTERN. AFTER ENJOYING A PERIOD OF HIGHLY FAVORABLE CONDITIONS LEADING TO A SECOND BOUT OF RAPID INTENSIFICATION, THE TABLES HAVE TURNED AND THE SYSTEM IS UNDERGOING AN EXTREMELY RAPID DECLINE. THE COMBINATION OF COOLER SSTS, RAPIDLY INCREASING VWS AND DRY AIR ENVELOPMENT WILL CONSPIRE TO CONTINUE TO WEAKEN THE SYSTEM THROUGH THE FORECAST PERIOD. SHEAR IS EXPECTED TO REACH 35-40 KNOTS WITHIN THE NEXT 12 HOURS, LEADING TO FULL DECAPITATION OF THE CONVECTIVE CORE WITH THE LOW LEVEL CIRCULATION CENTER LIKELY BECOMING EXPOSED WITHIN THE NEXT 12 TO 24 HOURS. THE SYSTEM IS FORECAST TO FULLY DISSIPATE BELOW THE 25 KNOTS WARNING THRESHOLD NO LATER THAN TAU 72, AND POTENTIALLY AS EARLY AS TAU 48, TO THE EAST OF HONG KONG. MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN GOOD AGREEMENT, AT LEAST THROUGH TAU 24. AFTER THIS POINT, AS THE SYSTEM WEAKENS BELOW TS STRENGTH, THE MODELS STRUGGLE TO MAINTAIN A CONSISTENT TRACK AND BEGIN TO SPREAD, BOTH ALONG AND CROSS-TRACK. THE JTWC FORECAST TRACKS THE LEFT EDGE OF THE GUIDANCE PACKAGE THROUGH TAU 12, THEN CURVES INSIDE AND SLOWER THAN THE BULK OF THE GUIDANCE THROUGH THE REMAINDER OF THE FORECAST. CONFIDENCE IS HIGH THROUGH TAU 24, THOUGH DECREASES TO LOW THEREAFTER DUE TO THE UNCERTAINTIES WITH THE TIMING OF DISSIPATION. INTENSITY GUIDANCE IS IN GOOD AGREEMENT, WITH ALL MODELS INDICATING RAPID WEAKENING. THE JTWC FORECAST DIVERGES FROM THE GUIDANCE AFTER TAU 36, CONTINUING TO WEAKENING AND DISSIPATION TREND, WHILE THE MAJORITY OF THE GUIDANCE KEEPS THE INTENSITY AT OR ABOVE 30-35 KNOTS AFTER TAU 48 AS THE TRACKERS HOLD ONTO THE VORTEX TO THE NORTHEAST OF TAIWAN. CONFIDENCE IS LOW IN THE JTWC INTENSITY FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: LOW// NNNN