WDPN31 PGTW 131500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (KOPPU) WARNING NR 
03//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 24W (KOPPU), LOCATED APPROXIMATELY 382 NM 
NORTH OF YAP, HAS TRACKED WESTWARD AT 11 KNOTS OVER THE PAST SIX 
HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A 
DEEPENING CENTRAL DENSE OVERCAST FEATURE OBSCURING THE LOW LEVEL 
CIRCULATION CENTER (LLCC). A 131136Z METOP-A MICROWAVE IMAGE SHOWS A 
CONSOLIDATED LLCC WITH DEFINED SHALLOW BANDING AND THE BULK OF 
CONVECTION CONFINED TO THE WESTERN SEMI-CIRCLE. THE CURRENT POSITION 
AND INTENSITY IS BASED ON A 131232Z ASCAT BULLSEYE WITH HIGH 
CONFIDENCE. UPPER LEVEL ANALYSIS INDICATES A MARGINALLY-FAVORABLE 
ENVIRONMENT WITH AN ANTICYCLONE JUST NORTH OF THE SYSTEM, PROVIDING 
STRONG DIVERGENT OUTFLOW. HOWEVER, MODERATE (15-20 KNOT) EASTERLY 
VERTICAL WIND SHEAR (VWS) IS PREVENTING FASTER INTENSIFICATION. SEA 
SURFACE TEMPERATURES (SSTS) ARE NEAR 30 CELSIUS. TD 24W IS TRACKING 
ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE 
(STR) TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC 
REASONING MESSAGE.
   B. TS KOPPU WILL CONTINUE TO TRACK WESTWARD THROUGH THE REMAINDER 
OF THE FORECAST PERIOD UNDER THE STEERING INFLUENCE OF THE STR TO 
THE NORTH. EXPECT SLOW INTENSIFICATION OVER THE NEXT 48 HOURS AS VWS 
CONTINUES TO HINDER DEVELOPMENT. BEYOND TAU 48, VWS WILL DROP BELOW 
15 KNOTS AND SSTS WILL INCREASE ABOVE 30 CELSIUS, SUPPORTING AN 
INCREASED RATE OF INTENSIFICATION AS THE SYSTEM APPROACHES LUZON.
   C. IN THE EXTENDED FORECAST, TS 24W WILL CONTINUE ON A WESTWARD 
TRACK AS THE STR REMAINS THE DOMINANT STEERING MECHANISM. THE STORM 
WILL SLOW AS IT REACHES THE WESTERN EXTENT OF THE STR AND UNDERGO A 
PERIOD OF RAPID INTENSIFICATION DUE TO THE VERY FAVORABLE 
ENVIRONMENTAL CONDITIONS. AFTERWARDS THE SYSTEM WILL WEAKEN DUE TO 
LAND INTERACTION AS IT MAKES LANDFALL OVER LUZON. DYNAMIC MODEL 
GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL TRACK; HOWEVER, A 
BIFURCATION REMAINS AT THE END OF THE FORECAST PERIOD WHEN THE 
CYCLONE REACHES LUZON. DUE TO THIS BIFURCATION IN THE MODEL 
GUIDANCE, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST.//
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