WDPN32 PGTW 050900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) WARNING 
NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 23W (ATSANI), LOCATED APPROXIMATELY 399 NM 
SOUTH-SOUTHWEST OF KADENA AB, OKINAWA, HAS TRACKED WESTWARD AT 09 
KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL 
SATELLITE IMAGERY (MSI) REVEALS A PARTIALLY-EXPOSED LOW LEVEL 
CIRCULATION CENTER (LLCC) OBSCURED BY THINNING CONVECTION LOCATED 
OVERHEAD. A 050521Z ATMS 88.2 GHZ MICROWAVE IMAGE DEPICTS BANDING 
WRAPPING INTO THE DISCRETE LLCC, LENDING GOOD CONFIDENCE TO THE 
INITIAL POSITION. HEDGED SLIGHTLY HIGHER THAN MULTI-AGENCY DVORAK 
CURRENT INTENSITY ESTIMATES OF T3.0 (45 KTS, PGTW/RJTD), THE 
INITIAL INTENSITY REMAINS AT 55 KTS BASED ON A 050429Z SATELLITE 
CONSENSUS ESTIMATE OF 55 KTS. THE 34- AND 50-KT WIND RADII HAVE 
BEEN UPDATED BASED ON THE 050245Z DIRECT ASCAT-B PASS. 
ENVIRONMENTAL ANALYSIS REVEALS AN OVERALL CONDUCIVE ENVIRONMENT FOR 
DEVELOPMENT CHARACTERIZED BY LOW (5-10 KT) VERTICAL WIND SHEAR 
(VWS), ESTABLISHED DUAL CHANNEL OUTFLOW, AND WARM (28-29 CELSIUS) 
SEA SURFACE TEMPERATURES (SST). TS 23W IS TRACKING GENERALLY 
WESTWARD ALONG THE SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR). 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 23W IS EXPECTED TO TRACK GENERALLY WESTWARD THROUGH TAU 12 
THEN TURN WEST-NORTHWESTWARD THROUGH TAU 36 AS IT BEGINS TO TRACK 
AROUND THE SOUTHEASTERN PERIPHERY OF THE AFOREMENTIONED STR. DURING 
THIS TIME, THE SYSTEM WILL STEADILY INTENSIFY TO 70 KTS DUE TO 
PERSISTENT FAVORABLE ENVIRONMENTAL CONDITIONS. AFTERWARDS, THE 
SYSTEM IS EXPECTED TO SLOWLY TURN TO A WEST-SOUTHWESTWARD TRACK AS 
A STR POSITIONED OVER CENTRAL CHINA TAKES OVER AS THE PRIMARY 
STEERING MECHANISM. THIS STEERING MECHANISM SHIFT WILL CAUSE THE 
SYSTEM TO TURN TO A SOUTHWESTWARD TRACK AFTER TAU 48. AT THIS TIME, 
THE SYSTEM WILL BEGIN TO EXPERIENCE INCREASING (>25 KTS) VWS WHICH 
WILL BEGIN TO WEAKEN THE SYSTEM TO 35 KTS BY TAU 72. NUMERICAL 
MODEL GUIDANCE IS IN TIGHT AGREEMENT THROUGH TAU 36. HOWEVER, 
NAVGEM AND GALWEM DIVERGE SIGNIFICANTLY FROM THE MULTI-MODEL 
CONSENSUS WITH NAVGEM TRACKING THE VORTEX GENERALLY NORTHWARD WHILE 
GALWEM TURNS THE SYSTEM SOUTH TOWARDS LUZON AT TAU 48. IN ORDER TO 
OFFSET THE EFFECTS OF THESE UNLIKELY SOLUTIONS, THE JTWC FORECAST 
TRACK IS POSITIONED SLIGHTLY SOUTH OF THE MULTI-MODEL CONSENSUS 
WITH GOOD CONFIDENCE. 
   C. IN THE EXTENDED FORECAST, TS 23W SHOULD CONTINUE TO TRACK 
SOUTHWESTWARD TOWARDS SOUTHERN VIETNAM ALONG THE SOUTHEASTERN 
PERIPHERY OF THE STR. AS IT WEAKENS, A MID-LEVEL RIDGE WILL 
CONTRIBUTE TO THE STEERING OF THE SYSTEM. CONTINUED HIGH VWS AND 
COOLING SST WILL STEADILY WEAKEN THE SYSTEM PRIOR TO LANDFALL OVER 
SOUTH CENTRAL VIETNAM. COMBINED WITH THE UNFAVORABLE ENVIRONMENT, 
TERRAIN INTERACTION AFTER LANDFALL WILL RAPIDLY WEAKEN THE SYSTEM 
UNTIL FULL DISSIPATION OVER LAND BY TAU 96. WITH THE EXCEPTION OF 
THE AFOREMENTIONED OUTLIERS, THERE REMAINS GOOD AGREEMENT IN THE 
EXTENDED RANG NUMERICAL MODEL GUIDANCE. THEREFORE, THERE IS GOOD 
CONFIDENCE IN THE JTWC FORECAST TRACK WHICH LIES ALONG THE MULTI-
MODEL CONSENSUS.//
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