Tropical Storm ATSANI Advisory jue, 05-11

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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