WDPN31 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (SAUDEL) WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS. 
   TYPHOON (TY) 19W (SAUDEL), LOCATED APPROXIMATELY 315 NM SOUTH-
SOUTHEAST OF HONG KONG, HAS TRACKED NORTH-NORTHWESTWARD AT 04 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE 
IMAGERY SHOWS PULSING CONVECTION WITH OVERSHOOTING TOPS JUST SOUTH 
OF THE ASSESSED CENTER LOCATION. THE DEEP CONVECTION HAS BECOME MORE 
SYMMETRICAL OVER THE PAST SIX HOURS, BUT THE MAJORITY OF THE 
CONVECTION IS CONFINED TO THE SOUTHERN SEMI-CIRCLE, WITH THE LLCC 
ASSESSED AS BEING IN THE NORTHERN EDGE OF THE CONVECTIVE MASS, 
GIVING THE SYSTEM AN ASYMMETRIC APPEARANCE. THE INITIAL POSITION IS 
PLACED WITH FAIR CONFIDENCE BASED ON THE OBSCURED LLCC, WITH SUPPORT 
PROVIDED BY A WEAKLY DEFINED MID-LEVEL CENTER EVIDENT IN A 221020Z 
SSMIS 91 GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS ASSESSED AT 
70 KNOTS WITH FAIR CONFIDENCE HEDGED SLIGHTLY LOWER THAN THE MULTI-
AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T4.5 (77 KNOTS) FROM 
PGTW AND RJTD IN LIGHT OF A KNES ESTIMATE OF DT4.0 (65 KNOTS), AN 
ADVANCED DVORAK TECHNIQUE (ADT) ESTIMATE OF T3.6 (57 KNOTS) AND A 
SATELLITE CONSENSUS ESTIMATE OF 64 KNOTS. ENVIRONMENTAL ANALYSIS 
REVEALS THE SYSTEM LIES IN AN OVERALL FAVORABLE ENVIRONMENT WITH LOW 
(15-20 KNOTS) VWS, WARM (28-29 DEG C) SSTS AND GOOD EQUATORWARD 
OUTFLOW AND WEAK POLEWARD OUTFLOW. TY 19W REMAINS IN A COL REGION 
BETWEEN STRS LOCATED EAST AND WEST OF THE SYSTEM, AND IS DRIFTING 
SLOWLY NORTH-NORTHWEST. IS MOVING SLOWLY NORTHWARD IN IN A WEAK 
STEERING ENVIRONMENT IN THE COL REGION BETWEEN SUBTROPICAL RIDGES 
LOCATED BOTH EAST AND WEST OF THE SYSTEM AND THE PASSAGE OF A MID-
LATITUDE MAJOR SHORTWAVE TROUGH PASSING TO THE NORTH. 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TY 19W IS FORECAST TO CONTINUE TO DRIFT SLOWLY NORTHWESTWARD 
OVER THE NEXT 12 HOURS IN THE WEAK STEERING ENVIRONMENT PROVIDING BY 
THE UPPER-LEVEL COL REGION. AS A MAJOR SHORTWAVE TROUGH PASSES TO 
THE NORTH OVER THE NEXT 12 HOURS, TY 19W WILL SLOWLY TRANSITION TO A 
MORE WESTWARD TRACK BY TAU 24 AS THE STR TO THE EAST BUILDS AND 
EXTENDS TO THE WEST OVER TAIWAN AND EASTERN CHINA. INTENSITY WILL 
REMAIN STEADY THROUGH TAU 12 AS THE UPWELLING OF COOLER WATERS WILL 
OFFSET THE MODERATE OUTFLOW AND LOW VWS. TY 19W WILL INTENSIFY 
SLIGHTLY TO A PEAK OF 75 KNOTS BY TAU 24 AS THE UPPER-LEVEL 
DIVERGENCE INCREASES FOR SHORT PERIOD, WHILE THE SYSTEM MOVES OUT OF 
THE COOLER, UPWELLED WATERS INTO AN AREA OF WARMER SSTS. THE 
INTENSIFICATION WILL BE BRIEF HOWEVER, AS INCREASING VWS AND MASS 
CONVERGENCE IN THE UPPER-LEVELS WILL COMBINE TO STEADILY WEAKEN THE 
SYSTEM AFTER TAU 72. NUMERICAL MODELS ARE IN TIGHT AGREEMENT WITH 
ONLY 130 NM SPREAD IN TRACKERS AT TAU 72 INCLUDING THE UKMET 
ENSEMBLE AS THE EXTREME OUTLIER TO THE SOUTH, AND ONLY 80 NM SPREAD 
IF THIS MODEL IS DISCOUNTED. IN LIGHT OF THE SLOW NORTHWARD MOVEMENT 
OVER TH PAST 12 HOURS, THE JTWC FORECAST TRACK TURNS WESTWARD AT A 
SLIGHTLY SLOWER RATE THAN THE MODEL TRACKERS, WITH THE RESULT THAT 
THE OFFICIAL FORECAST TRACK LIES ON THE NORTHERN EDGE OF THE 
GUIDANCE ENVELOPE THROUGH TAU 36, THEN COMES MORE IN LINE WITH THE 
CONSENSUS THROUGH TAU 72. THERE IS LOW CONFIDENCE IN THIS PORTION OF 
THE FORECAST TRACK PRIMARILY DUE TO THE INTRICACIES IN TIMING OF THE 
TURN TO THE WEST.
   C. BEYOND TAU 72, TY SAUDEL WILL TURN WESTWARD AND THEN 
SOUTHWESTWARD AS 
THE STR TO THE WEST BECOMES THE DOMINATE STEERING MECHANISM. THE 
SYSTEM WILL MAKE LANDFALL BETWEEN TAU 72 AND 96 TO THE NORTH OF HUE, 
VIETNAM, THEN CONTINUE INLAND WHILE DISSIPATING BY TAU 120 OVER THE 
RUGGED TERRAIN. MODEL GUIDANCE DIVERGES SIGNIFICANTLY AFTER TAU 72, 
WITH THE ECMWF AND JGSM TAKING THE SYSTEM INTO NORTHERN LAOS, WHILE 
THE NVGM AND ECMWF ENSEMBLE TAKE THE MIDDLE ROUTE INTO CENTRAL 
THAILAND AND THE GFS AND GFS ENSEMBLE TAKE THE SYSTEM WELL SOUTH 
INTO CAMBODIA. THE JTWC OFFICIAL TRACK LIES NEAR THE MULTI-MODEL 
CONSENSUS WITH LOW CONFIDENCE DUE TO THE BIFURCATION IN THE 
GUIDANCE.//
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