WDPN31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (ETAU) 
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 24W (ETAU), LOCATED APPROXIMATELY 269 NM
SOUTHEAST OF DA NANG, VIETNAM, HAS TRACKED WEST-SOUTHWESTWARD 
AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED 
SATELLITE IMAGERY (EIR) DEPICTS A WEAKENING SYSTEM WITH DEEP 
CONVECTION SHEARED OVER THE WESTERN PERIPHERY OF A PARTIALLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL
POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON THE POSITION 
OF THE PARTIALLY EXPOSED LLCC IN THE EIR LOOP AS WELL AS VIA 
EXTRAPOLATION THROUGH THE BANDING FEATURES PRESENT IN A 091500Z 
GMI 37 GHZ IMAGE. ANALYSIS OF MICROWAVE IMAGERY INDICATES THAT 
THE DEEP CONVECTION HAS BECOME FURTHER DECOUPLED FROM THE LLCC
DURING THE LAST 6 HOURS. THE INITIAL INTENSITY IS ASSESSED AT 
35 KTS WITH FAIR CONFIDENCE BASED ON MULTI-AGENCY DVORAK CURRENT
INTENSITY ESTIMATES OF T2.0 (30 KTS, PGTW) AND T2.5 (35 KTS, 
RJTD). ENVIRONMENTAL ANALYSIS REVEALS A RAPIDLY DETERIORATING 
ENVIRONMENT, WITH COOLING SSTS (26-27 DEG CELSIUS) AND MODERATE TO 
HIGH (20-25 KNOTS) EASTERLY VWS OFFSETTING THE CONTINUED ROBUST 
WESTWARD OUTFLOW ALOFT. DUE TO THE EFFECTS OF THE CONTINUED 
DECOUPLING OVER THE PAST SIX HOURS, THE PRIMARY STEERING INFLUENCE 
IS LIKELY SHIFTING TO THE LOW LEVEL EAST-NORTHEASTERLY FLOW, 
RESULTING IN THE WEST-SOUTHWESTWARD TRACK MOTION SEEN IN THE PAST 
SIX HOURS. 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 24W IS FORECAST TO BEGIN A GENERALLY WESTWARD TRACK 
THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD. THROUGH TAU 12,
THE ENVIRONMENT WILL REMAIN MARGINAL AND AS A RESULT IS EXPECTED TO
SUPPORT AN INTENSITY OF 35 KTS. AT TAU 12 TS ETAU WILL MAKE LANDFALL 
ALONG THE SOUTH-CENTRAL VIETNAM COAST AND BEGIN TO DISSIPATE OVER 
LAND DUE TO CONTINUED MODERATE TO HIGH VWS AND INTERACTION WITH THE
UNDERLYING TERRAIN. AS THE SYSTEM CENTER MOVES FURTHER INLAND, IT
WILL CONTINUE TO WEAKEN AND COMPLETE DISSIPATION OVER LAND BY TAU
36. NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT WITH A SPREAD OF 
60NM AT LANDFALL. THIS SPREAD IN SOLUTIONS INCREASES THEREAFTER AS 
THE VARIOUS MODELS LOSE THE VORTEX SIGNATURE DUE TO THE RAPID DECAY
OF THE SYSTEM OVER LAND. THE JTWC FORECAST IS SET SLIGHTLY SOUTH OF 
THE MULTI-MODEL CONSENSUS IN LIGHT OF THE RECENT TRACK MOTION AND 
SHIFT IN THE STEERING MECHANISM WITH HIGH CONFIDENCE.//
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