WDPN32 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 19W (CHANTHU) WARNING NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.4N 129.1E
   INITIAL INTENSITY: 135 KTS
   GEOGRAPHIC REFERENCE: 472 NM EAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT 
AND SYMMETRICAL SYSTEM THAT HAS MAINTAINED CONVECTIVE STRUCTURE WITH 
A WELL-DEFINED, SHARPLY-OUTLINED 5-NM PINHOLE EYE. STY 19W CONTINUES 
TO TRACK WESTWARD WITH INDICATIONS OF A SLIGHT WOBBLE TO THE SOUTH 
FROM 1630Z TO 1830Z. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON THE EYE FEATURE IN THE EIR LOOP THAT STACKED 
VERTICALLY DOWN TO THE LOW LEVEL CIRCULATION CENTER. THE INITIAL 
INTENSITY OF 135 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 
HIGH END OF AGENCY DVORAK ESTIMATES AND REFLECTS THE SUSTAINED EIR 
CONVECTIVE SIGNATURE. ANALYSIS INDICATED A FAVORABLE ENVIRONMENT 
WITH LOW VWS, STRONG RADIAL OUTFLOW AND VERY WARM SST. THE CYCLONE 
IS TRACKING WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STR TO THE 
NORTH.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   KNES: T7.0 - 140 KTS 
   CIMSS SATCON: 110 KTS AT 081655Z
   CIMSS ADT: 112 KTS AT 081740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: INCREASE TO FORECAST INTENSITIES IN 
THE 
NEAR TO MID-TERM DUE TO EVIDENCE OF THE EYEWALL REPLACEMENT CYCLE 
HAVING BEEN COMPLETED.

FORECAST DISCUSSION: STY 19W WILL CONTINUE TO TRACK WESTWARD THROUGH 
TAU 12 THEN BEGIN TO TURN TO THE NORTHWEST BY TAU 24 AS THE SYSTEM 
BEGINS TO ROUND THE STR. DURING THIS TIME THE SYSTEM WILL INCREASE 
TO ITS MAX INTENSITY OF 140 KTS. THIS INCREASE IS DUE TO THE 
FAVORABLE ENVIRONMENT WITH LOW VWS, STRONG RADIAL OUTFLOW AND HIGH 
SST. STY 19W WILL CONTINUE THIS NORTHWESTWARD TRACK UNTIL TAU 72, AT 
WHICH IT WILL TURN TO MORE OF A NORTHWARD TRACK JUST TO THE 
SOUTHWEST OF TAIWAN AS IT APPROACHES TO STR AXIS. INTERACTION WITH 
LUZON BY TAU 36, FURTHER INTERACTION WITH TAIWAN BY TAU 72, AND 
INCREASING VWS WILL LEND TO A GRADUAL DECREASE IN INTENSITY TO 105 
KTS BY TAU 72. BY TAU 96, STY 19W WILL MAKE LANDFALL JUST TO THE 
WEST OF XIAMEN, CHINA WITH A DECREASED INTENSITY TO 90 KTS. THE 
ADDITION OF FRICTIONAL EFFECTS FROM LAND INTERACTION WILL RAPIDLY 
ERODE 19W TO 60KTS BY TAU 120 AS IT PASSES 
SOUTHWEST OF HANGZHOU, CHINA.

MODEL DISCUSSION: OVERALL TRACK GUIDANCE IS IN GOOD AGREEMENT WITH
A 75 NM SPREAD AT TAU 24, GRADUALLY INCREASING TO A 150 NM SPREAD
BY TAU 48. AFTER TAU 48 TRACK GUIDANCE BECOMES RATHER ERRATIC WITH
A 420 NM SPREAD AT TAU 120, LENDING TO LOW CONFIDENCE IN FORECAST
TRACK AFTER TAU 72. NAVGEM'S TRACK HAS BEEN IDENTIFIED AS THE
OUTLIER WITH A VERY SHARP JOG TO THE NORTHEAST BY TAU 72, SO THIS
TRACKER WAS NOT TAKEN INTO CONSIDERATION WITH THE JTWC TRACK.
INTENSITY CONSENSUS (ICNW) MAINLY FAVORS A RELATIVELY WEAKER SYSTEM
THROUGHOUT THE FORECAST. THE JTWC INTENSITY FORECAST IS HEDGED
HIGHER THAN ICNW DUE TO THE SYSTEM ENTERING A LOW VWS, HIGH OHC
ENVIRONMENT, LENDING TO MEDIUM CONFIDENCE IN FORECAST INTENSITY
DURING THE FIRST 72 HOURS. AFTER TAU 72, THERE IS LOW CONFIDENCE IN
FORECAST INTENSITY.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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