MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 02W (SANBA) WARNING NR 17// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 02W (SANBA), LOCATED APPROXIMATELY 496 NM SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 19 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A RAPIDLY MOVING SYSTEM WITH DEEP CONVECTION CONFINED TO THE NORTHERN SEMI-CIRCLE. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION WHICH IS BASED ON A LOW REFLECTIVITY CIRCULATION FEATURE OBSERVED IN A 121811Z 89GHZ GMI IMAGE WITH A PATCH OF DEEP CONVECTION EMANATING FROM THE CENTER AND A BAND OF DEEP CONVECTION ON THE NORTHERN PERIPHERY. THE INITIAL INTENSITY IS ASSESSED AT 35 KNOTS WHICH IS HEDGED TO THE HIGHER END OF CURRENT INTENSITY DVORAK ESTIMATES RANGING FROM T2.0 TO T2.5 (25 TO 30 KNOTS). A 121320Z METOP-B ASCAT IMAGE SHOWS THE INTACT LOW LEVEL CIRCULATION CENTER WITH THE HIGHEST WINDS LOCATED TO THE NORTH AND EXTENDING NORTHWEST JUST OFFSHORE FROM THE PHILIPPINES. TS 02W IS TRACKING NORTHWESTWARD ALONG THE SOUTHWESTERN BOUNDARY OF A DEEP- LAYERED SUBTROPICAL RIDGE (STR) ANCHORED TO THE NORTHEAST AND EXTENDING WESTWARD OVER THE SOUTH CHINA SEA. THE POSITION OF THE RIDGE AXIS IS CREATING GOOD DIFFLUENT CONDITIONS ALOFT AND TS 02W IS TRACKING RAPIDLY IN PHASE WITH THE EASTERLY FLOW MINIMIZING THE INFLUENCE OF VERTICAL WIND SHEAR. 3. FORECAST REASONING. A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 02W WILL CONTINUE TRACKING GENERALLY WESTWARD OVER THE FORECAST PERIOD ALONG THE SOUTHERN BOUNDARY OF THE STR EXTENSION. AN ONGOING COLD SURGE EVENT IN THE MID-LATITUDES OFF THE ASIAN COAST IS BRINGING ENHANCED NORTHEASTERLY WINDS INTO THE REGION AND FEEDING INTO TS 02W AND EXPANDING THE GALE WIND RADII TO MAINLY THE NORTHERN PORTIONS OF THE FORECAST TRACK. THE ENHANCED FLOW IS EXPECTED TO PERSIST OVER THE NEXT 36 TO 48 HOURS AND, WITH AN OTHERWISE FAVORABLE ENVIRONMENT, LEAD TO A MAXIMUM INTENSITY OF 40 KNOTS AT TAU 48. BUT TS 02W WILL FIRST WEAKEN SLIGHTLY AS IT TRACKS OVER THE SOUTHERN ISLANDS OF THE PHILIPPINES. THE LOW LEVEL CIRCULATION IS EXPECTED TO REMAIN INTACT RECONSOLIDATING QUICKLY AS IT EMERGES OVER THE SULU SEA. C. IN THE EXTENDED TAUS, TS 02W WILL WEAKEN GRADUALLY AS IT TRACKS WEST-NORTHWESTWARD OVER THE SOUTH CHINA SEA AND ENCOUNTERS COOLER SEA SURFACE TEMPERATURES AS IT APPROACHES VIETNAM. VERTICAL WIND SHEAR IS ALSO EXPECTED TO INCREASE UNDER THE PREDOMINANT EASTERLY FLOW ALOFT. TS 02W IS FORECAST TO DISSIPATE COMPLETELY SHORTLY AFTER MAKING LANDFALL OVER VIETNAM NEAR TAU 102. DYNAMIC MODEL GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH TAU 48 LENDING HIGH CONFIDENCE TO THIS PORTION OF THE FORECAST TRACK. BEYOND TAU 48 THE GUIDANCE DIFFERS SOMEWHAT WITH COAMPS SHOWING A TRACK SOUTH OF 10 DEGREES NORTH. NAVGEM AND THE JAPANESE ENSEMBLE ARE THE NORTHERN MOST OUTLIERS SHOWING A MORE PRONOUNCED TURN TO THE NORTHWEST. DUE TO THE FADING CONFIDENCE IN THE EXTENDED FORECAST TRACK, THERE IS OVERALL LOW CONFIDENCE IN THE FORECAST TRACK.// NNNN NNNN