WDPN32 PGTW 040900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) 
WARNING NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 23W (ATSANI), LOCATED APPROXIMATELY 379NM SOUTH OF 
KADENA AB, HAS TRACKED NORTHWESTWARD AT 03 KNOTS OVER THE PAST SIX 
HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) INDICATES THAT 
THE SYSTEM HAS BECOME QUASI-STATIONARY, WITH THE LOW LEVEL 
CIRCULATION CENTER (LLCC) OBSCURED BY FLARING DEEP CONVECTION. THE 
INITIAL POSITION IS PLACED WITH ONLY FAIR CONFIDENCE DUE TO THE 
OBSCURED LLCC, WITH A 040458Z AMSR2 89 GHZ MICROWAVE IMAGE LENDING 
SUPPORT TO THE INITIAL POSITION. THE INITIAL INTENSITY IS 
ASSESSED WITH FAIR CONFIDENCE ON AN ANALYSIS OF THE PGTW DVORAK 
CURRENT INTENSITY ESTIMATE OF T3.0 (45 KNOTS), AN ADVANCED DVORAK 
TECHNIQUE (ADT) ESTIMATE OF T3.2 AND A SATELLITE CONSENSUS ESTIMATE 
OF 46 KNOTS. TS 23W LIES IN AN OVERALL FAVORABLE ENVIRONMENT, WITH 
LOW (5-10 KNOTS) OF EASTERLY VWS, GOOD EQUATORWARD AND POLEWARD 
OUTFLOW AND WARM (28 TO 29 DEG CELSIUS) SSTS. INITIAL MOTION HAS 
BEEN ERRATIC OVER THE PAST 12 HOURS IN A WEAK STEERING ENVIRONMENT, 
AND IT APPEARS AS IF THE CENTER IS CURRENTLY LOOPING BACK TO THE 
NORTH AND WEST BASED ON ANIMATED VISIBLE IMAGERY. 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. WHILE THE NEAR-TERM MOTION REMAINS ERRATIC, ANALYSIS OF THE 
DEEP-LAYER MEAN FLOW IN THE GLOBAL MODELS AND 500MB ANALYSIS 
INDICATE THAT THE STR TO THE NORTHEAST HAS ALREADY BEGUN TO BUILD 
WESTWARD, WITH RIDGING FORECAST TO BUILD WEST OVER TAIWAN AND 
EASTERN CHINA BY TAU 24, EFFECTIVELY ELIMINATING THE COL REGION IN 
WHICH TS 23W CURRENTLY IS ENSCONCED, PUSHING THE SYSTEM ONTO A 
WESTWARD TRACK BY TAU 12. AS THE RIDGE BECOMES MORE ENTRENCHED TO 
THE NORTH, TS 23W WILL ACCELERATE WHILE CONTINUING WESTWARD THROUGH 
TAU 72. THE SYSTEM IS FORECAST TO STEADILY INTENSIFY TO A PEAK OF 65 
KNOTS BY TAU 48 UNDER GENERALLY SUPPORTIVE CONDITIONS OF LOW (5 TO 
15 KNOTS) VWS, SINGLE CHANNEL DIVERGENT WESTWARD OUTFLOW AND 
RELATIVELY WARM (28 TO 29 DEG CELSIUS). DYNAMIC MODEL GUIDANCE IS IN 
VERY GOOD AGREEMENT THROUGH 72, WITH THE NOTABLE EXCEPTION OF 
NAVGEM, WHICH CONTINUES TO SHOW AN UNREALISTIC NORTHWESTWARD TRACK 
TOWARDS TAIWAN. THE JTWC FORECAST LIES ALONG THE NORTHERN EDGE OF 
GUIDANCE ENVELOPE THROUGH TAU 24 IN LIGHT OF THE NEAR-TERM 
NORTHWESTWARD MOVEMENT, THEN NEAR THE MULTI-MODEL CONSENSUS SOLUTION 
THROUGH TAU 72 WITH FAIR CONFIDENCE.  
   C. IN THE EXTENDED TAUS, THE SYSTEM WILL ENTER THE NORTHERN 
PORTION OF THE SOUTH CHINA SEA BY TAU 72 ON A GENERALLY WESTWARD 
TRACK AS STRONG TROPICAL STORM. HOWEVER, THE COMBINATION OF 
INCREASED VWS, CONVERGENT UPPER-LEVEL FLOW, THE ENTRAINMENT OF 
DRIER, COOLER AIR FROM THE NORTH, AND COOLER SSTS WILL COMBINE TO 
STEADILY WEAKEN THE SYSTEM THROUGH TAU 120. AS THE SYSTEM WEAKENS, 
AND VORTEX BECOMES WEAKER, IT WILL COME UNDER THE STEERING INFLUENCE 
OF THE LOW TO MID-LEVEL FLOW FROM THE NORTHEAST, PUSHING THE SYSTEM 
ONTO A SOUTHWESTWARD TRACK AFTER TAU 72. TS 23W IS FORECAST TO MAKE 
LANDFALL ALONG THE SOUTHERN VIETNAMESE COASTLINE JUST PRIOR TO TAU 
120 AS A WEAK TROPICAL STORM, BEFORE CONTINUING TO TRACK INLAND 
TOWARDS THE SOUTHWEST. DYNAMIC MODEL GUIDANCE IS IN OVERALL GOOD 
AGREEMENT, WITH CROSS-TRACK SPREAD INCREASING TO 185 NM BY TAU 120. 
NOTABLY, THE NAVGEM AND ECMWF MODELS TAKE THE SYSTEM POLEWARD 
TOWARDS THE TAIWAN STRAIT AND LOSE THE VORTEX BY TAU 96, WHICH IS 
SKEWING THE MULTI-MODEL CONSENSUS FURTHER TO THE NORTH. THE JTWC 
FORECAST DISCOUNTS THESE TWO MODELS, AND LIES ALONG THE SOUTHERN 
SIDE OF THE CONSENSUS ENVELOPE. HOWEVER, IN VIEW OF THE UNCERTAINTY 
IN THE EXACT TIMING OF THE TURN SOUTHWARD, THERE IS LOW CONFIDENCE 
IN THIS PORTION OF THE FORECAST TRACK.// 
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