MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (HAISHEN) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 11W (HAISHEN), LOCATED APPROXIMATELY 336 NM SOUTH OF IWO TO, HAS TRACKED WESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS SPIRAL BANDING WRAPPING INTO A LOW LEVEL CIRCULATION CENTER (LLCC) THAT IS CURRENTLY OBSCURED BY AN 88 NM DIAMETER AREA OF CENTRAL DENSE OVERCAST. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON THE MSI LOOP AND A MICROWAVE EYE FEATURE PRESENT IN RECENT 020645Z SSMIS 91 GHZ AND 37 GHZ IMAGERY. THE INITIAL INTENSITY OF 65 KTS IS PLACED WITH FAIR CONFIDENCE AND IS HEDGED ABOVE A PGTW DVORAK CURRENT INTENSITY ESTIMATE OF T3.5 (55 KTS) BASED ON THE WIND FIELD DATA IN A 020401Z AMSR2 PASS. THE SYSTEM IS TRACKING ALONG THE COMBINED STEERING INFLUENCE OF A SUBTROPICAL RIDGE (STR) TO THE WEST AND AN EXTENSION OF THE STR TO THE NORTHEAST AND THROUGH A FAVORABLE ENVIRONMENT OF VERY WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURES (SST), LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS) AND ROBUST EQUATORWARD OUTFLOW ALOFT. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE LAST PROGNOSTIC REASONING MESSAGE. B. A MIDLATITUDE SHORTWAVE TROUGH APPROACHING FROM THE NORTHWEST HAS BEGUN TO ERODE THE STR TO THE WEST WHILE THE STR TO THE NORTHEAST HAS BEGUN TO BUILD AND IS NOW TAKING OVER AS THE PRIMARY STEERING MECHANISM FOR THE SYSTEM. THE INFLUENCE OF THIS STEERING RIDGE WILL DRIVE THE SYSTEM WEST-NORTHWESTWARD THROUGH TAU 72. INITIALLY, HIGHLY FAVORABLE ENVIRONMENTAL CONDITIONS OF LOW (5-15 KTS) VWS, VERY WARM (30-31 CELSIUS) SST AND CONTINUED DIVERGENT FLOW ALOFT WILL ALLOW THE SYSTEM TO INTENSIFY TO 110 KTS BY TAU 48. THERE IS A DISTINCT POSSIBILITY OF RAPID INTENSIFICATION DURING THIS TIME DUE TO THE HIGHLY FAVORABLE ENVIRONMENTAL CONDITIONS. THIS INTENSIFICATION TREND WILL SLOW AFTER TAU 48 AS TY HAISHEN BEGINS A MORE NORTHWESTWARD TRACK DUE TO INCREASING, MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS), RESULTING IN A PEAK INTENSITY OF 120 KTS BY TAU 72. NUMERICAL MODEL SOLUTIONS ARE IN FAIR AGREEMENT THROUGH TAU 72 WITH A MAXIMUM 96 NM SPREAD DURING THIS TIME. DESPITE THIS TIGHT AGREEMENT IN MODEL SOLUTIONS, THE MODEL TRACKS HAVE CONTINUED TO DRIVE WESTWARD WITH SUCCESSIVE COMPUTATIONAL RUNS. THIS DRIFT IN MODEL SOLUTIONS OVER TIME LENDS ONLY FAIR CONFIDENCE IN THE INITIAL PORTION OF THE JTWC FORECAST TRACK. C. BEYOND TAU 72, TY HAISHEN WILL CONTINUE TO TRACK NORTHWESTWARD ALONG THE PERIPHERY OF THE DOMINANT STR, NOW TO THE EAST. CONTINUED FAVORABLE CONDITIONS WILL ALLOW THE SYSTEM TO MAINTAIN ITS PEAK INTENSITY OF 120 KTS THROUGH TAU 96 AS IT BEGINS ITS APPROACH TOWARDS THE KOREAN PENINSULA. BETWEEN TAU 96 AND TAU 120, TY HAISHEN WILL TRACK WEST OF KYUSHU AND CROSS THE KOREAN STRAIT, ULTIMATELY MAKING LANDFALL OVER SOUTH KOREA NEAR BUSAN BEFORE TAU 120. AT THIS TIME THE INTENSITY WILL DROP RAPIDLY DUE TO THE FRICTIONAL EFFECTS OF THE UNDERLYING TERRAIN AND THE SYSTEM WILL BEGIN EXTRATROPICAL TRANSITION (ETT) AS IT APPROACHES THE BAROCLINIC ZONE. NUMERICAL MODEL SOLUTIONS ARE IN TIGHT AGREEMENT FOR THIS EXTENDED PORTION OF THE JTWC FORECAST, HOWEVER THE AFOREMENTIONED DRIFT IN MODEL SOLUTIONS OVER THE PAST 48 HOURS OF COMPUTATIONAL SIMULATIONS REDUCES THE CONFIDENCE IN TRACK GUIDANCE, DESPITE THE HIGH DEGREE OF TRACK AGREEMENT. DUE TO THIS ANALYSIS, THERE IS ONLY FAIR CONFIDENCE ASSESSED IN THE OVERALL JTWC FORECAST TRACK. // NNNN NNNN