WDPN32 PGTW 152100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (CHANTHU) WARNING 
NR 039//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.3N 125.2E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 285 NM SOUTHWEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TS 19W HAS TRACKED ERRATICALLY WITH A LOOP EVIDENT OVER THE
PAST 18 HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY SHOWS A CONSOLIDATING LOW-LEVEL CIRCULATION WITH
IMPROVED DEEP CONVECTIVE BANDING WRAPPING INTO A DEFINED
CENTER. A 151710Z ATMS 88.2GHZ LOW-RESOLUTION IMAGE DEPICTS
DEEP CONVECTIVE BANDING OVER THE NORTH AND WEST QUADRANTS
WRAPPING INTO A RAGGED CENTER, WHICH SUPPORTS THE INITIAL
POSITION WITH MEDIUM CONFIDENCE. THE INITIAL INTENSITY IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE RECENT ADT
ESTIMATE, HEDGED ABOVE THE AGENCY DVORAK ESTIMATES BASED
ON THE IMPROVED CONVECTIVE STRUCTURE. POLEWARD OUTFLOW
REMAINS ROBUST, WHICH IS AIDING THE RECENT INTENSIFICATION,
AND VERTICAL WIND SHEAR REMAINS FAVORABLE AS WELL. 

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE EXTENSION TO THE
EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 49 KTS AT 1210Z
   CIMSS ADT: 49 KTS AT 151740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE 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: TS 19W IS FORECAST TO TRACK NORTHWARD TO
NORTHEASTWARD AS THE SUBTROPICAL RIDGE BUILDS INTO WESTERN JAPAN
IN RESPONSE TO AN APPROACHING MIDLATITUDE RIDGE. THE SYSTEM WILL
ACCELERATE EAST-NORTHEASTWARD AFTER TAU 24 AS STRONG WESTERLY
FLOW DEVELOPS OVER SOUTH KOREA AND HONSHU. TS 19W IS FORECAST
TO INTENSIFY SLIGHTLY TO 55 KNOTS BY TAU 12 UNDER FAVORABLE
CONDITIONS BUT SHOULD WEAKEN DUE TO INCREASING VERTICAL WIND
SHEAR AND COOLER SST VALUES NEAR KYUSHU. AS THE SYSTEM TRACKS
JUST NORTH OF SASEBO NEAR TAU 36, IT WILL BEGIN TO INTERACT WITH
THE BAROCLINIC ZONE AND JET, AND WILL WEAKEN TO 45 KNOTS AS IT
BEGINS EXTRA-TROPICAL TRANSITION (ETT). TS 19W WILL CONTINUE TO
TRACK ACROSS WESTERN JAPAN, WEAKEN FURTHER AND COMPLETE ETT
NEAR CENTRAL HONSHU UNDER JET STRENGTH WESTERLIES. THE CENTER
SHOULD BROADEN DURING THIS PHASE WITH DEEP CONVECTION DECAYING
RAPIDLY. THE SYSTEM IS EXPECTED TO MAINTAIN GALE-FORCE WINDS,
WHICH SHOULD BECOME HIGHLY ASYMMETRIC.   

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
THROUGH TAU 36 WITH A 27NM SPREAD IN SOLUTIONS AT TAU 36. AFTER
TAU 36, MODEL GUIDANCE DIVERGES AS THE SYSTEM GAINS FRONTAL
CHARACTERISTICS AND THE EXACT CENTER POSITION BROADENS AND
BECOMES INCREASINGLY UNCERTAIN. OVERALL, CONFIDENCE IN THE JTWC
FORECAST TRACK IS MEDIUM WITH UNCERTAINTY IN THE RECURVE TIMING
OVER THE NEXT 36 HOURS. THE JTWC FORECAST TRACK IS POSITIONED
CLOSE TO THE JTWC MULTI-MODEL CONSENSUS (CONW). THERE IS MEDIUM
CONFIDENCE IN THE JTWC INTENSITY FORECAST AS WELL WITH SOME
POTENTIAL IN A SLIGHTLY HIGHER PEAK INTENSITY OVER THE NEXT 24
HOURS UNTIL ENVIRONMENTAL CONDITIONS DEGRADE.    

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