WDPN31 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (SAUDEL) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS. 
   TYPHOON (TY) 19W (SAUDEL), LOCATED APPROXIMATELY 287 NM SOUTH-
SOUTHEAST OF HONG KONG, HAS TRACKED WEST-NORTHWESTWARD AT 06 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE 
IMAGERY SHOWS THE SYSTEM CONTINUED TO IMPROVE WITH DEEPENED CENTRAL 
CONVECTION AND FEEDER BANDS WRAPPING TIGHTLY INTO AN OBSCURED LOW 
LEVEL CIRCULATION. SANS ANY RECENT MICROWAVE IMAGERY AND ASCAT 
PASSES, THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON 
A LOOSE CLUSTER OF AGENCY FIXES AND EXTRAPOLATION FROM CURRENT STORM 
MOTION. THE INITIAL INTENSITY OF 75KTS IS BASED ON THE DVORAK 
ESTIMATES OF T4.5/77KTS FROM PGTW AND KNES AND CONSISTENT WITH THE 
IMPROVED EIR STRUCTURE. THE ENVIRONMENT REMAINS FAVORABLE WITH LOW 
(10-15KT) VERTICAL WIND SHEAR (VWS), WARM (29C) SEA SURFACE 
TEMPERATURES (SST) IN THE SOUTH CHINA SEA, AND NEAR-RADIAL 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 BY TAU 72. THE 
FAVORABLE CONDITIONS WILL FUEL FURTHER INTENSIFICATION TO A PEAK OF 
80KTS BY TAU 12. AFTERWARD, COOLING SSTS CAUSED BY TC-INDUCED 
UPWELLING AND DECREASING OUTFLOW WITH THE RECEDING TROUGH WILL 
GRADUALLY WEAKEN THE SYSTEM TO 60KTS BY TAU 48, AND RAPIDLY TO 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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