MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (THIRTEEN) WARNING NR 05// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 13W (THIRTEEN), LOCATED APPROXIMATELY 430 NM NORTH- NORTHWEST OF WAKE ISLAND, HAS TRACKED NORTHWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) SHOWS THE DEEPEST CONVECTION REMAINS ALONG THE NORTHERN HALF OF THE SYSTEM WITH FLARING CENTRAL CONVECTION OVER THE PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC). THE TRACK HAS BEEN STEADILY NORTHWARD UNDER THE INFLUENCE OF THE BUILDING NEAR EQUATORIAL RIDGE TO THE SOUTHEAST OF THE LLCC. EIR ALSO INDICATES THAT THE POLEWARD OUTFLOW IS BEGINNING TO IMPROVE IN ASSOCIATION WITH THE HIGH AMPLITUDE TROUGH CURRENTLY LOCATED TO THE NORTH OF THE SYSTEM. UPPER LEVEL ANALYSIS INDICATES THERE REMAINS A WEAKENING OUTFLOW CHANNEL TO THE SOUTHEAST INTO AN EASTWARD TRACKING TROPICAL UPPER TROPOSPHERIC TROUGH. ADDITIONALLY, THE LLCC IS LOCATED WITHIN A REGION OF MODERATE VERTICAL WIND SHEAR (VWS) (10 TO 20 KNOTS). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TS 13W IS EXPECTED TO CONTINUE TRACKING NORTHWARD OVER THE NEXT 24 HOURS, WITH A BUILDING SUBTROPICAL RIDGE TO THE NORTHEAST SLOWLY SHIFTING THE TRACK TO THE NORTHWEST THROUGH TAU 72. IMPROVING OUTFLOW OVER THE NEXT 36 HOURS WILL ALLOW FOR MODEST INTENSIFICATION. CURRENTLY FAVORABLE SEA SURFACE TEMPERATURES (SSTS) WILL SUPPORT THIS INCREASE; HOWEVER AROUND TAU 36, THE LLCC WILL MOVE INTO A REGION OF UNFAVORABLE SSTS. INCREASING VWS WILL BEGIN TO HINDER DEVELOPMENT BEYOND TAU 36 WITH A WEAKENING TREND EXPECTED BEYOND TAU 48. C. BEYOND TAU 72, DECREASING SST'S AND PERSISTENTLY HIGH VWS WILL ERODE THE SYSTEM DOWN TO 25 KNOTS BY END OF FORECAST PERIOD. THERE IS HIGH CONFIDENCE IN THE TRACK FORECAST UP TO TAU 48, AFTER TAU 48, THE NUMERICAL MODELS SIGNIFICANTLY DIFFER WITH RESPECT TO TRACK SPEEDS. GFS AND ECMWF ARE SIGNIFICANTLY FASTER THAN THE CONSENSUS. THIS FORECAST IS CLOSER IN LINE WITH NGPS BASED ON THE FORECASTED TRACK SPEEDS REMAINING SLOWER IN THE EXTENDED TAUS AROUND THE STR. DUE TO THE VARIANCE IN THE MODEL GUIDANCE, THERE IS A LOW CONFIDENCE IN THE TRACK FORECAST BEYOND TAU 48.// NNNN NNNN