MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (NEOGURI) WARNING NR 011// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (NEOGURI), LOCATED APPROXIMATELY 324 NM SOUTH OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTAL SATELLITE IMAGERY (MSI) SHOWS A COMPACT MIDGET SYSTEM (95NM ACROSS) THAT CONTINUES TO SLOWLY CONSOLIDATE AND BECOME MORE SYMMETRICAL. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON WARM PIXELS IN THE 182340Z INFRARED SATELLITE IMAGE, ADJUSTED FOR SLAND, AND LINED UP WITH WITH A NOTCH FEATURE IN THE 182246Z SSMIS 91GHZ MICROWAVE PASS. THE INITIAL INTENSITY OF 55KTS IS BASED ON CONGRUENT DVORAK ESTIMATES OF T3.5/55KTS FROM PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS INDICATES MODERATE (15-20KT) VERTICAL WIND SHEAR (VWS) THAT IS OFFSET BY POLEWARD OUTFLOW AND THE STORM MOTION THAT IS IN-PHASE WITH UPPER LEVEL WIND FLOW. SEA SURFACE TEMPERATURES (SSTS) ARE ALSO CONDUCIVE AT 28-29C, HOWEVER THIS IS TEMPERED BY A COLD DRY NORTHERLY SURGE IN THE PHILIPPINE SEA. OVERALL, THE ENVIRONMENT IS MARGINALLY FAVORABLE. THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE; HOWEVER, THE EXTENDED FORECAST ALONG TRACK SPEEDS WERE INCREASED. B. TS 21W WILL CONTINUE IN ITS CURRENT TRACK, STEERED BY THE STR, AND WILL CREST THE STR AXIS BY TAU 12. AFTERWARD, IT WILL RECURVE NORTHEASTWARD ON THE POLEWARD SIDE OF THE STR AND GRADUALLY ACCELERATE. THE OVERALL FAVORABLE CONDITIONS, ENHANCED BY STRONG POLEWARD OUTFLOW AS THE SYSTEM APPROACHES THE PREVAILING WESETRLIES, WILL PROMOTE MODERATE INTENSIFICATION TO A PEAK OF 60KTS AT TAUS 12- 24. AFTERWARD, INCREASING VWS AND COOLING SSTS WILL GRADUALLY ERODE THE SYSTEM DOWN TO 35KTS BY TAU 72. THE NUMERICAL MODELS ARE IN GENERAL AGREEMENT TO THIS TRACK WITH ECMWF THE NOTABLE OUTLIER BRINGING THE VORTEX MORE WESTWARD AND SLOWER. THERE IS FAIR CONFIDENCE IN THIS PORTION OF THE JTWC TRACK FORECAST THAT IS LAID JUST TO THE EAST OF AND SLOWER THAN MODEL CONSENSUS TO OFFSET ECMWF. C. BEYOND TAU 72, TS 21W IS EXPECTED TO CONTINUE ACCELERATING NORTHEASTWARD. CONCURRENTLY, IT WILL BEGIN EXTRA-TROPICAL TRANSITION. INCREASING VWS AND COOLING SSTS WILL DEGRADE THE SYSTEM TO 35KTS BY TAU 96; HOWEVER, EXPECT THE INTENSITY TO INCREASE TO 40KTS AS IT GETS EMBEDDED IN THE BAROCLINIC ZONE AND TRANSFORMS A COLD-CORE LOW WITH AN EXPANSIVE WIND FIELD BY TAU 120. NUMERICAL MODELS SIGNIFICANTLY SPREAD OUT AND DEVIATE IN ALONG-TRACK SPEEDS BEYOND TAU 72, LENDING LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC TRACK FORECAST.// NNNN NNNN