MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (TWENTYSEVEN) WARNING NR 17// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 27W (TWENTYSEVEN), LOCATED APPROXIMATELY 234 NM SOUTH OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS THE SYSTEM CONTINUED TO STRUGGLE AS THE BROAD AREA OF DEEP BUT DISORGANIZED CONVECTION FED LOOSELY INTO AN ILL-DEFINED AND OBSCURED LOW LEVEL CIRCULATION. THE INITIAL POSITION IS EXTRAPOLATED FROM LOW REFLECTIVITY PERIPHERAL CIRCULATION OUTLINES IN THE 231652Z SSMI 37 GHZ PASS WITH LOW CONFIDENCE. THE INITIAL INTENSITY HAS BEEN REDUCED TO 35 KNOTS BUT STILL HELD HIGHER THAN AGENCY DVORAK ESTIMATES; HOWEVER, IT IS SUPPORTED BY SATCON DVORAK ESTIMATES RANGING FROM T2.5-T2.6. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM IS IN AN AREA OF MODERATE (15-20 KNOT) VERTICAL WIND SHEAR (VWS) THAT IS PARTLY OFFSET BY EQUATORWARD OUTFLOW AND A STORM MOTION THAT IS IN-PHASE WITH THE UPPER AND LOW LEVEL WIND FLOW. HOWEVER, A TUTT CELL TO THE NORTHEAST, JUST EAST OF GUAM, IS CAUSING SUBSIDENCE AND INHIBITING POLEWARD OUTFLOW. SSTS IN THE REGION ARE VERY WARM AT 30 CELSIUS. THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN EXTENSION OF A BUILDING SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. THE PEAK INTENSIFICATION PHASE HAS BEEN ADJUSTED TOWARD THE TERMINATION OF THE FORECAST, OTHERWISE, THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. AT THE ONSET, TS 27W WILL DEVELOP AT A VERY SLOW RATE AS THE LOW LEVEL CIRCULATION STRUGGLES TO CONSOLIDATE AND THE TUTT CELL STIFLES POLEWARD OUTFLOW. TS 27W WILL GRADUALLY TRACK NORTHWESTWARD IN THE WARM PHILIPPINE SEA AS THE STR CONTINUES TO BUILD AND STEER THE SYSTEM. AS IT MOVES AWAY FROM THE TUTT CELL AND AS IT EVENTUALLY CONSOLIDATES, TS 27W WILL INTENSIFY AT A NEAR CLIMATOLOGICAL RATE AND REACH TYPHOON INTENSITY OF 65 KNOTS BY TAU 48. AFTER TAU 48, HOWEVER, AS THE SYSTEM ENCOUNTERS STRONG VWS AHEAD OF AN APPROACHING MID-LATITUDE TROUGH, THE INTENSITY WILL BE SUSTAINED AT BEST, MAYBE EVEN REDUCED. NUMERIC MODEL GUIDANCE IS IN GOOD AGREEMENT DURING THIS PORTION OF THE JTWC TRACK FORECAST, LENDING HIGH CONFIDENCE UP TO TAU 72. C. IN THE EXTENDED PERIOD, TS 27W WILL ROUND THE WESTERN EDGE OF THE STR AND TURN MORE NORTHWARD THEN ACCELERATE NORTHEASTWARD, ON THE FRONT EDGE OF THE AFOREMENTIONED MID-LATITUDE TROUGH. BY TAU 120 THE CYCLONE WILL BE NEAR 30N, SOUTH OF HONSHU, JAPAN. INCREASED OUTFLOW ASSOCIATED WITH THE MID-LATITUDE TROUGH AND IN PHASE-STORM MOTION WILL PROMOTE A SECONDARY INTENSIFICATION PHASE, REACHING 90 KNOTS BY END OF FORECAST. MODEL GUIDANCE SHOWS A LARGER SEPARATION IN THE LATER TAUS WITH THE JAPANESE MODELS ON THE EXTREME RIGHT OF THE MODEL ENVELOPE SHOWING AN UNREALISTIC TURN INTO THE STEERING RIDGE. THE JTWC FORECAST TRACK IS HEDGED JUST LEFT OF THE MULTI-MODEL CONSENSUS WITH LOW CONFIDENCE.// NNNN NNNN