WDPN32 PGTW 132100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (CHANTHU) WARNING NR 031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.5N 123.5E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 306 NM SOUTH-SOUTHWEST OF KUNSAN AB, SOUTH
KOREA
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM
HAS MOSTLY MAINTAINED ITS CONVECTIVE WRAP SIGNATURE EVEN AS RAIN
BANDS COLLAPSE AND BECOME FRAYED NORTHEASTWARD WITH THE STRONG
MIDLATITUDE WESTERLIES. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE ON THE CENTRAL PIXELS IN THE EIR, ADJUSTED FOR EASTWARD
TILT. THE INITIAL INTENSITY IS ASSESSED BASED ON THE MEDIAN OF
AGENCY AND AUTOMATED DVORAK ESTIMATES AND REFLECTS THE SUSTAINED
EIR SIGNATURE. ANALYSIS INDICATES THE CYCLONE IS LODGED IN A COL
AREA WITH OVERALL MARGINALLY UNFAVORABLE CONDITIONS CHARACTERIZED
BY STRONG POLEWARD OUTFLOW AND COOLING SSTS OFFSET BY MEDIUM TO
STRONG VWS.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: COL BETWEEN SUBTROPICAL RIDGE (STR) TO
THE WEST AND STR TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.5 - 77 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 45 KTS AT 131740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TY CHANTU IS EXPECTED TO BECOME QUASI-
STATIONARY (QS) OVER THE NEXT TWO DAYS IN THE COL. AFTERWARD, THE 
STR TO THE NORTHWEST WILL WEAKEN, ALLOWING THE SECONDARY STR TO THE 
SOUTHEAST TO ASSUME STEERING AND DRIVE THE SYSTEM NORTHEASTWARD 
TOWARD THE SEA OF JAPAN (SOJ), CROSS NORTHERN HONSHU OVER MISAWA, 
EXIT INTO THE PACIFIC OCEAN, AND BY TAU 120 WILL BE EAST OF 
HOKKAIDO. THE MARGINALLY FAVORABLE CONDITIONS, EXACERBATED BY 
FURTHER COOLING OF THE SSTS AS THE QS SYSTEM GENERATES UPWELLING OF 
DEEP COLD WATER, WILL PROMOTE STEADY WEAKENING DOWN TO 45KTS BY TAU 
48. AFTERWARD, THE NORTHEASTWARD TRACK INTO HIGHER VWS AND COLDER 
SSTS OF THE SOJ WILL FURTHER WEAKEN IT TO 40KTS BY TAU 96. 
CONCURRENTLY BY TAU 72, TY 19W WILL BEGIN EXTRA-TROPICAL TRANSITION 
AND BY TAU 96 WILL TRANSFORM INTO A GALE-FORCE COLD-CORE LOW. BY TAU 
120, THE SYSTEM WILL BE FULLY EMBEDDED IN THE BAROCLINIC FLOW IN THE 
PACIFIC OCEAN WITH AN EXPANDING WIND FIELD.  

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT;
HOWEVER, GIVEN THE UNCERTAINTY IN THE STORM MOTION AND DURATION IN
THE COL AREA, THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST
THAT IS LAID CLOSE TO THE MODEL CONSENSUS.  

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