WDPN32 PGTW 170300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (CHANTHU) WARNING 
NR 044//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.9N 127.5E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 111 NM WEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
FULLY-EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER WITH
SHALLOW BANDING AND ISOLATED, FLARING CONVECTION SHEARED TO THE
EAST. ANIMATED RADAR IMAGERY REVEALS A BROADENING BUT DEFINED
CENTER WITH RAINBANDS AND EXTENSIVE AREAS OF HEAVY RAINFALL OVER
THE NORTHERN SEMICIRCLE. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE MSI. THE INITIAL INTENSITY OF 45 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW AND RJTD DVORAK
ESTIMATES, WHICH IS CONSISTENT WITH THE OVERALL CONVECTIVE
STRUCTURE. A BUOY OBSERVATION FROM 22187, 50NM WEST OF THE CENTER
AT 170200Z, INDICATES NORTHERLY WINDS AT 33 KNOTS. SURFACE
OBSERVATIONS ALONG THE WESTERN COAST OF KYUSHU HAVE GRADUALLY
INCREASED AND RANGE FROM 20-23 KNOTS (10 MINUTE AVERAGE). POLEWARD
OUTFLOW INTO THE WESTERLIES REMAINS VIGOROUS WITH MODERATE TO
STRONG (20-25 KNOTS) WESTERLY VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR). 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 35 KTS AT 162330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 19W IS ROUNDING THE NORTHWEST PERIPHERY OF
THE STR AND IS FORECAST TO TRACK NORTHEASTWARD OVER THE NEXT 12
HOURS, PASSING CLOSE TO SASEBO WITH 45 KNOT SUSTAINED WINDS. AFTER
TAU 12, TS 19W WILL TRACK GENERALLY EASTWARD ALONG THE NORTHERN
PERIPHERY OF THE STR UNDER UPPER-LEVEL WESTERLY FLOW WITH 25-30
KNOTS OF VWS. INTERACTION WITH THE ROUGH TERRAIN WILL CONTRIBUTE TO
A STEADY WEAKENING TREND THROUGH TAU 36. TS 19W IS EXPECTED TO
UNDERGO EXTRA-TROPICAL TRANSITION (ETT) WITH A FRONTAL STRUCTURE
EVIDENT IN THE 850MB TEMPERATURE FIELD REVEALING SIGNIFICANT COLD
AIR ADVECTION OVER WESTERN JAPAN BY TAU 36 AND A REGION OF WARM AIR
ADVECTION OVER THE KANTO PLAIN EXTENDING INTO A DEVELOPING
TRIPLE-POINT LOW OVER NORTHERN HONSHU. THE LOW OVER NORTHERN
HONSHU IS EXPECTED TO BE THE DOMINANT LOW WITH 19W MERGING WITH THE
FRONTAL BOUNDARY ALONG THE TAIL END. DUE TO THIS SCENARIO, THERE
IS INCREASING UNCERTAINTY IN THE FORECAST TRACK AFTER TAU 36 WITH A
SLOW EASTWARD TO EAST-SOUTHEASTWARD TRACK. THERE IS A POSSIBILITY
THE SYSTEM MAY WEAKEN FURTHER OVER WATER AND DISSIPATE. HOWEVER,
THE SYSTEM IS EXPECTED TO COMPLETE ETT BY TAU 36 AND WILL REMAIN
AN EXTRA-TROPICAL LOW THROUGH TAU 72. 

MODEL DISCUSSION: WITH THE EXCEPTION OF GALWEM (AFUM), WHICH TRACKS
THE SYSTEM INTO NORTHERN HONSHU, NUMERICAL MODEL GUIDANCE IS IN
GOOD AGREEMENT THROUGH TAU 36 WITH A 65NM 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 SIGNIFICANT UNCERTAINTY IN THE EXACT
TRACK AFTER TAU 36. THE JTWC FORECAST TRACK IS POSITIONED CLOSE TO
THE JTWC MULTI-MODEL CONSENSUS (CONW). OVERALL, THERE IS MEDIUM 
CONFIDENCE IN THE JTWC INTENSITY FORECAST.

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