WDPN31 PGTW 230300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (SAUDEL) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS. 
   TYPHOON (TY) 19W (SAUDEL), LOCATED APPROXIMATELY 277 NM SOUTH-
SOUTHEAST OF HONG KONG, HAS TRACKED WEST-NORTHWESTWARD AT 05 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY 
SHOWS THE SYSTEM CONTINUED TO IMPROVE WITH DEEPENED AND MORE COMPACT 
CENTRAL CONVECTION WITH OVERSHOOTING CLOUD TOPS NEAR AN IMMINENT EYE 
FEATURE. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED 
ON A DEFINED MICROWAVE EYE IN THE 222046Z AND 222254Z SSMIS IMAGES. THE  
INITIAL INTENSITY OF 85KTS IS BASED ON AGENCY DVORAK ESTIMATES RANGING  
FROM T4.5/77KTS (KNES) AND T5.0/90KTS (PGTW AND RJTD). THE ENVIRONMENT 
IS NOW MARGINALLY FAVORABLE AS VERTICAL WIND SHEAR (VWS) HAS INCREASED 
TO MODERATE (15-20KTS); HOWEVER, THIS IS OFFSET BY WARM (29C) SEA 
SURFACE TEMPERATURES (SST) IN THE SOUTH CHINA SEA, AND ROBUST UPPER-
LEVEL OUTFLOW. THE CYCLONE IS IN A COL CREATED BY A SHORTWAVE TROUGH 
DIGGING INTO TAIWAN THAT SPLIT THE STEERING SUBTROPICAL RIDGE (STR)INTO 
TWO - ONE TO THE WEST AND ONE TO THE EAST, WHICH IS CURRENTLY THE 
DOMINANT STEERING MECHANISM.     
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. THE STR TO THE EAST IS EXPECTED TO RE-BUILD AS THE SHORTWAVE 
TROUGH ADVANCES EASTWARD, ALLOWING TY 19W TO TRACK SLOWLY ON A MORE 
WESTWARD DIRECTION, PASSING JUST SOUTH OF HAINAN, CHINA, AND MAKING 
LANDFALL OVER CENTRAL VIETNAM, JUST NORTH OF HUE NEAR TAU 66. THE 
MARGINALLY FAVORABLE CONDITIONS WILL MAINTAIN THE CURRENT INTENSITY UP 
TO TAU 12. AFTERWARD, COOLING SSTS CAUSED BY TC-INDUCED UPWELLING, 
MODERATE VWS, AND DECREASING OUTFLOW WITH THE RECEDING TROUGH WILL 
GRADUALLY WEAKEN THE SYSTEM TO 60KTS BY TAU 48, AND RAPIDLY DOWN TO 
30KTS BY TAU 72 WITH LAND INTERACTION AFTER LANDFALL. NUMERICAL MODELS 
ARE IN BETTER AGREEMENT WITH UEMN THE SOLE LEFT OUTLIER, LENDING FAIR 
CONFIDENCE TO THIS PORTION OF THE JTWC TRACK FORECAST. 
   C. AFTER TAU 72, TY SAUDEL WILL TRACK MORE WEST-SOUTHWESTWARD AS THE 
STR TO THE WEST BECOMES THE DOMINANT STEERING MECHANISM, CROSSING LAOS 
AND INTO THAILAND BY TAU 96 WHERE IT WILL DISSIPATE DUE TO FRICTIONAL 
EFFECTS OF THE RUGGED TERRAIN. MODEL GUIDANCE DIVERGES SIGNIFICANTLY 
AFTER TAU 72 AS SOME MODELS LOSE THE WEAK VORTEX, LENDING LOW 
CONFIDENCE TO THIS PORTION OF THE JTWC TRACK FORECAST. 
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