WDPN32 PGTW 060900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) WARNING NR 
032//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 23W (ATSANI), LOCATED APPROXIMATELY 224 NM 
SOUTH OF TAIPEI, TAIWAN, HAS TRACKED WEST-NORTHWESTWARD AT 10 KNOTS 
(KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) DEPICTS BUILDING CONVECTION OBSCURING A LOW LEVEL 
CIRCULATION CENTER (LLCC). BASED ON THE MSI, RADAR IMAGERY, AND AN 
EXTRAPOLATION OF A 060446Z AMSR2 89 GHZ MICROWAVE IMAGE SHOWING 
TIGHT BANDING WRAPPING INTO A LLCC, THERE IS GOOD CONFIDENCE IN THE 
INITIAL POSITION. THE INITIAL INTENSITY REMAINS ASSESSED AT 45 KTS 
WITH GOOD CONFIDENCE BASED ON MULTI-AGENCY DVORAK CURRENT INTENSITY 
ESTIMATES OF T3.0 (45 KTS, PGTW/RJTD) ALONG WITH A 060146Z CIMSS 
SATELLITE CONSENSUS INTENSITY ESTIMATE OF 45 KTS AND RECENT ASCAT 
DATA SHOWING SWATHS OF 40-45 KT WINDS IN THE NORTHERN QUADRANT. 
OVERALL, TS 23W REMAINS IN A HIGHLY CONDUCIVE ENVIRONMENT FOR 
DEVELOPMENT CHARACTERIZED BY LOW (5-10 KTS) VERTICAL WIND SHEAR 
(VWS), WARM (27-28 CELSIUS) SEA SURFACE TEMPERATURES (SST), AND 
POLEWARD AND EQUATORWARD OUTFLOW CHANNELS. TS 23W IS TRACKING ALONG 
THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED 
TO THE NORTHEAST. 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 23W IS EXPECTED TO TRACK GENERALLY WEST-NORTHWESTWARD 
THROUGH TAU 12 AS IT TRANSITS ALONG THE SOUTHWESTERN PERIPHERY OF 
THE STR, INTENSIFYING TO 55 KTS DUE TO PERSISTENT FAVORABLE 
ENVIRONMENTAL CONDITIONS. AFTERWARDS, THE SYSTEM SHOULD TURN TO A 
WESTWARD THEN SOUTHWESTWARD TRACK AS A STR POSITIONED OVER CENTRAL 
CHINA TAKES OVER AS THE PRIMARY STEERING MECHANISM. DURING THIS 
TIME, INCREASING VWS WILL BEGIN TO WEAKEN THE SYSTEM AS IT TRACKS 
SOUTHWESTWARD OVER SLIGHTLY COOLER (26-27 CELSIUS) SST. THE SYSTEM 
IS EXPECTED TO FULLY DISSIPATE OVER WATER BY TAU 72 AS IT ENCOUNTERS 
CONTINUED HIGH (30+ KT) VWS. NUMERICAL GUIDANCE IS IN GOOD AGREEMENT 
THROUGH TAU 36. HOWEVER, THE MODEL SOLUTIONS BEGIN TO DIVERGE 
AFTERWARDS, LIKELY DUE TO DIFFERENCES IN THE TIMING WHEN THE STR 
OVER CENTRAL CHINA BECOMES THE PRIMARY STEERING MECHANISM. 
ADDITIONALLY, SEVERAL MODELS MAINTAIN A WESTWARD TRACK RATHER THAN 
TURNING THE SYSTEM SOUTHWESTWARD AFTER TAU 24. BASED ON THIS 
UNCERTAINTY, THERE IS OVERALL POOR CONFIDENCE IN THE JTWC FORECAST 
TRACK WHICH LIES NEAR THE MULTI-MODEL CONSENSUS.//
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