WDPN33 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 31W (HAIYAN) WARNING NR 
22//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 31W (HAIYAN), LOCATED APPROXIMATELY 170 NM SOUTHWARD OF
MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 20 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR)  
SHOWS A CONTINUED WEAKENING TREND AS THE DEEP CONVECTION AROUND THE 
CLOUD-FILLED EYE HAS CONTINUED TO SHALLOW. THE INITIAL POSITION IS 
BASED ON THIS CLOUD-FILLED EYE SEEN IN THE EIR ANIMATION ALONG WITH 
POSITION FIXES FROM PGTW AND RJTD. THE INITIAL INTENSITY OF 135 
KNOTS IS BASED ON DECREASING DVORAK INTENSITY ESTIMATES FROM ALL 
REPORTING AGENCIES THAT RANGE FROM 115 TO 155 KNOTS AND THE OVERALL 
WEAKENING STRUCTURE OF THE SYSTEM. UPPER LEVEL ANALYSIS INDICATES 
THE SYSTEM HAS MAINTAINED STRONG RADIAL OUTFLOW IN AN OVERALL LOW 
(05 TO 10 KNOTS) VERTICAL WIND SHEAR (VWS) ENVIRONMENT. STY 31W IS 
CURRENTLY TRACKING ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYERED 
SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. IN THE EARLY TAUS, STY 31W IS EXPECTED TO MAINTAIN A WEST- 
NORTHWESTWARD TRACK ALONG THE SOUTHERN EDGE OF THE STR, SHIFTING TO 
A MORE NORTHWESTWARD TRACK BETWEEN TAU 48 AND 72, AFTER LANDFALL. 
THE SYSTEM IS EXPECTED TO MAINTAIN SUPER TYPHOON STRENGTH FOR THE 
NEXT 12 HOURS, DESPITE A SLOW WEAKENING TREND WHICH IS IN PART TO THE
AFOREMENTIONED FRICTIONAL EFFECTS AND A SLIGHT INCREASE IN VWS. 
AFTER TAU 24 A FASTER DECREASE IN INTENSITY IS EXPECTED DUE TO 
FURTHER DEGRADING ENVIRONMENTAL FACTORS OF MARGINAL SEA SURFACE 
TEMPERATURES IN THE WESTERN SOUTH CHINA SEA AND INCREASED LAND 
INTERACTION AS THE SYSTEM APPROACHES THE CENTRAL COAST OF VIETNAM. 
STY 31W IS EXPECTED TO MAKE LANDFALL NEAR TAU 48 OVER CENTRAL 
VIETNAM. AFTER LANDFALL, THE RUGGED TERRAIN WILL RAPIDLY WEAKEN THE 
SYSTEM AS IT BEGINS TO DISSIPATE.
   C. IN THE EXTENDED TAUS, STY 31W IS FORECAST TO TRACK MORE 
POLEWARD ALONG A BREAK IN THE STR AXIS DUE TO INTERACTION WITH A MID-
LATITUDE TROUGH THAT IS CURRENTLY LOCATED OVER CENTRAL CHINA. AS STY 
31W DRAGS ACROSS VIETNAM, THE LAND EFFECTS WILL CONTINUE TO ERODE 
THE SYSTEM WHICH IS EXPECTED TO DISSIPATE BY TAU 96. DYNAMIC MODEL 
GUIDANCE CONTINUES TO REMAIN IN TIGHT AGREEMENT LENDING TO HIGH 
CONFIDENCE IN THE FORECAST TRACK.//
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