WDPN32 PGTW 110300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 19W (CHANTHU) WARNING NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.3N 122.0E
   INITIAL INTENSITY: 145 KTS
   GEOGRAPHIC REFERENCE: 490 NM SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 55 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
WHILE UNDERGOING AN EYEWALL REPLACEMENT CYCLE AND ABSORBING INVEST 
96W, STY 19W HAS WEAKENED SIGNIFICANTLY OVER THE PAST SIX HOURS WITH 
THE LOSS OF THE EYE AND WARMING CLOUD TOP TEMPERATURES. 
ADDITIONALLY, ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A 
MORE ASYMMETRIC CONVECTIVE STRUCTURE, WHICH MAY SIGNAL A MORE RAPID 
WEAKENING TREND. OVERALL, CONFIDENCE IN THE INITIAL POSITION REMAINS 
HIGH. THE INITIAL INTENSITY IS ASSESSED AS MEDIUM CONFIDENCE BASED 
ON DVORAK ESTIMATES RANGING FROM 7.0 TO 7.5 AND THE ADT ESTIMATE. 
UPPER-LEVEL CONDITIONS HAVE REMAINED HIGHLY FAVORABLE WITH STRONG 
RADIAL OUTFLOW AND ENHANCED POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYERED, NORTH-SOUTH ORIENTED
SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST AND NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.5 - 155 KTS
   RJTD: T7.5 - 155 KTS
   RCTP: T7.5 - 155 KTS
   KNES: T7.0 - 140 KTS 
   CIMSS ADT: 146 KTS AT 102330Z

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: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: AS STY 19W TRACKS AWAY FROM NORTHERN LUZON
AND COMPLETES ERC, THE CONVECTIVE STRUCTURE WILL LIKELY IMPROVE AGAIN
THUS THE FORECAST IS MAINTAINED AT STY STRENGTH THROUGH TAU 12.
AFTER TAU 12, STY 19W WILL TRACK POLEWARD ALONG THE WESTERN
PERIPHERY OF THE STR AND WILL STEADILY WEAKEN AS IT INTERACTS WITH
TAIWAN. AFTER TAU 48, THE SYSTEM WILL INTERACT WITH AN UPPER-LEVEL
SUBTROPICAL TROUGH AND STEADILY WEAKEN AS IT BECOMES EMBEDDED
WITHIN THE TROUGH WITH CONVERGENT UPPER-LEVEL FLOW AND UNFAVORABLE
LEVELS OF MID-LEVEL VERTICAL WIND SHEAR. IN THE EXTENDED PERIOD,
STY 19W IS FORECAST TO TRACK SLOWLY EASTWARD WITHIN WEAK WESTERLY
FLOW AND WILL WEAKEN TO TS STRENGTH (50-55 KNOTS) BY TAU 120.
GLOBAL MODEL GUIDANCE INDICATES A FAIRLY ATYPICAL MIDLATITUDE
PATTERN WITH WEAK SUBTROPICAL WESTERLIES AND THE FRONTAL ZONE TO
THE NORTH OVER THE KOREAN PENINSULA, THEREFORE, EXTRATROPICAL
TRANSITION IS NOT LIKELY. ADDITIONALLY, TRACK SPEEDS SHOULD BE
UNUSUALLY SLOW.   

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
THROUGH TAU 72 WITH A 145NM SPREAD IN SOLUTIONS AT TAU 72 LENDING
HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. AFTER TAU 72, THERE IS
INCREASING UNCERTAINTY WITH WEAKER STEERING FLOW THUS MEDIUM TRACK
CONFIDENCE. OVERALL, THERE IS MEDIUM CONFIDENCE IN THE JTWC
INTENSITY FORECAST DUE TO THE COMPLEX INTERACTIONS WITH THE
AFOREMENTIONED TROUGH AND SUBTROPICAL WESTERLIES AS WELL AS
INTERACTION WITH TAIWAN AND EASTERN CHINA.   

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