WDPN32 PGTW 162100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (CHANTHU) WARNING 
NR 043//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.3N 126.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 159 NM WEST-SOUTHWEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY INDICATES DECAYING
DEEP CONVECTION WITH A DEFINED LOW-LEVEL CIRCULATION CENTER;
HOWEVER, A 161730Z ASMSR2 36GHZ IMAGE AND RADAR IMAGERY DEPICT
TIGHTLY-WRAPPED SHALLOW BANDING WRAPPING INTO A WELL-DEFINED
LOW-LEVEL CIRCULATION CENTER. THUS, THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED 
WITH MEDIUM CONFIDENCE BASED ON THE CIMSS SATCON ESTIMATE, WHICH IS 
CONSISTENT WITH THE OVERALL CONVECTIVE STRUCTURE. SURFACE 
OBSERVATIONS OVER THE NORTHERN (NEAR CHEJU DO) AND WESTERN 
PERIPHERIES (NORTHEAST OF SHANGHAI) OF THE SYSTEM RANGE AS HIGH AS 
30 TO 40 KNOTS. 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
   RCTP: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 50 KTS AT 161740Z
   CIMSS ADT: 39 KTS AT 161730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 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 BEGINNING TO ACCELERATE NORTHEASTWARD. OVER THE NEXT
12 HOURS, THE SYSTEM WILL TRACK EAST-NORTHEASTWARD NEAR SASEBO AND
GRADUALLY WEAKEN TO 45 KNOTS DUE TO PERSISTENT VWS, INTERACTION
WITH LAND AND MID-LEVEL DRY AIR ENTRAINMENT. AFTER TAU 12, TS 19W
WILL TRACK EAST-NORTHEASTWARD TO EASTWARD ALONG THE NORTHERN
PERIPHERY OF THE STR UNDER UPPER-LEVEL WESTERLY FLOW WITH 25-30
KNOTS OF VWS AND INTERACTION WITH THE ROUGH TERRAIN CONTRIBUTING 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: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 24 WITH A 76NM SPREAD IN SOLUTIONS AT TAU 24. AFTER TAU
24, 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 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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