WDPN32 PGTW 160900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (CHANTHU) WARNING 
NR 041//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.1N 125.4E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 249 NM WEST-SOUTHWEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM 19W APPEARS TO HAVE FINALLY STARTED ITS LONG-AWAITED
TRACK TOWARDS THE NORTHEAST. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS A VERY WELL DEFINED SWIRL OF LOW-LEVEL CLOUD
BANDS WRAPPING INTO A LOW-LEVEL CIRCULATION CENTER (LLCC) OBSCURED
BY FLARING CONVECTION EXTENDING SOUTHWARD FROM THE ASSESSED CENTER
POSITION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED
ON THE ANIMATED VISIBLE IMAGERY, AND WITHIN THE CONGRUENCE OF
AGENCY FIX POSITIONS. THE INITIAL INTENSITY REMAINS ASSESSED AT 55
KNOTS WITH MEDIUM CONFIDENCE BASED ON THE MEDIAN OF THE AGENCY
CURRENT INTENSITY ESTIMATES, HEDGED SLIGHTLY HIGHER THAN THE ADT
AND SATCON ESTIMATES.  THE OVERALL STRUCTURE APPEARS SHEARED WITH
AN AREA TO THE NORTH OF THE LLCC DEVOID OF ANY SIGNIFICANT
CONVECTION. ANALYSIS OF A 160000Z UPPER-AIR SOUNDING FROM HEUKSANDO
INDICATE THE PRESENCE OF VERY DRY AIR BETWEEN 300-600MB, WHICH
SUPPORTS WHAT IS SEEN IN THE IMAGERY. ADDITIONALLY, WHILE
HIGH-RESOLUTION HWRF SOUNDINGS AND CIMSS AUTOMATED UPPER-LEVEL
ANALYSIS REVEALS LOW SOUTHERLY WIND SHEAR, THE SHARP NORTHERN EDGE
OF THE CONVECTION FLARING NEAR THE CENTER CLEARLY SUPPORT A
NORTHERLY SHEAR VECTOR OVER TOP OF THE SYSTEM, AND THE LATEST CIMSS
ATMOSPHERIC MOTION VECTOR (AMV) ANALYSIS SUGGESTS THE PRESENCE OF A
SMALL, WEAK ANTICYCLONE JUST NORTHWEST OF THE LLCC, WHICH WOULD
SUPPORT A NORTHERLY WIND AT 200MB OVER TOP OF 19W. EXCEPTING THE
DRY AIR AND THE NORTHERLY SHEAR, THE ENVIRONMENT OTHERWISE
FAVORABLE WITH WARM SSTS AND ROBUST POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED TO THE
SOUTHEAST OF KYUSHU.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 52 KTS AT 160134Z
   CIMSS ADT: 49 KTS AT 160540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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. HOWEVER, THE CURRENT
FORECAST INCLUDES THE POTENTIAL OF AN ALTERNATE SCENARIO. 

FORECAST DISCUSSION: HAVING NOW BEGUN ITS TRACK TOWARDS THE
NORTHEAST, TS 19W IS FORECAST TO CONTINUE ACCELERATING
NORTHEASTWARD, TURNING MORE EASTWARD THROUGH THE DURATION OF THE
FORECAST, AHEAD OF AN APPROACHING MID-LATITUDE TROUGH AND ALONG THE
NORTHERN PERIPHERY OF THE DEEP STR TO THE SOUTHEAST. THE SYSTEM IS
EXPECTED TO MAKE LANDFALL ALONG THE NORTHWESTERN COAST OF KYUSHU
NEAR TAU 24, TRACK OVER THE INLAND SEA AND CROSS JUST SOUTH OF
TOKYO BETWEEN TAU 48 AND 60. THERE REMAINS A SHORT WINDOW OF
OPPORTUNITY FOR INTENSIFICATION OVER THE NEXT 12-18 HOURS AS THE
VWS REMAINS RELATIVELY LOW WHILE AT THE SAME TIME THE SYSTEM
CONTINUES TO TAP INTO ROBUST POLEWARD OUTFLOW. GOING INTO THE
DIURNAL MAXIMUM THIS EVENING, THE SYSTEM SHOULD INTENSIFY UP TO 60
KNOTS BY TAU 12. ONCE OVER LAND AND TRAVERSING THE INLAND SEA, THE
SYSTEM IS EXPECTED TO STEADILY WEAKEN DUE TO INCREASING VWS AND
TERRAIN INTERACTION. AS TS 19W MAKES LANDFALL IT IS EXPECTED TO
BEGIN INTERACTING WITH A WEAK BAROCLINIC ZONE CURRENTLY LYING
ACROSS SOUTHERN KOREA AND JAPAN, AND BEGIN TO EXTRA-TROPICAL
TRANSITION (ETT). AS THE SYSTEM COMPLETES ETT, THE WIND FIELD IS
FORECAST TO INCREASE AND BECOME INCREASINGLY ASYMMETRIC, WHILE THE
LLCC WILL BROADEN OUT AND DEEP CONVECTION WILL RAPIDLY DECAY. THE
SYSTEM IS EXPECTED TO COMPLETE ETT BY TAU 48 AS A GALE-FORCE LOW AS
IT TRANSITS THE SOUTHERN COAST OF HONSHU. THERE ALSO EXISTS THE
POTENTIAL FOR AN ALTERNATE SCENARIO BASED ON THE LATEST GLOBAL
MODEL FIELDS, MANY OF WHICH NOW INDICATE A SIGNIFICANTLY WEAKER
SYSTEM UNDERGOING ETT WHILE MOVING WELL SOUTH OF TOKYO AND BECOMING
QUASI-STATIONARY TO THE SOUTH-SOUTHEAST OF TOKYO. IN THIS SCENARIO
THE VORTICITY ASSOCIATED WITH TS 19W SPLITS AFTER LANDFALL, WITH AN
AREA MOVING TO THE NORTH OF HONSHU AND BECOMING EXTRA-TROPICAL,
WHILE THE REMAINDER TRACKS THROUGH THE INLAND SEA AND REMAINS
TROPICAL. THE REMNANTS OF THIS AREA OF VORTICITY THEN TRACK SOUTH
OF TOKYO, BUT LACKING DEEP CORE OF CONVECTION, DOES NOT STRONGLY
INTERACT WITH THE MID-LATITUDE TROUGH TO THE NORTH, AND THUS
SIMULTANEOUSLY DISSIPATES WHILE COMPLETING ETT.

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH
LANDFALL, WITH ALL GUIDANCE MEMBERS CLOSELY CLUSTERED ABOUT THE
MEAN WITH A LANDFALL ALONG THE NORTHWEST COAST OF KYUSHU AT TAU 24.
THEREAFTER THE GUIDANCE DIVERGES, WITH HWRF AND GALWEM JUMPING
CIRCULATION CENTERS AND TRACKING THE NORTHERN, SECONDARY LOW
DISCUSSED ABOVE AS THE ALTERNATE SCENARIO. THE REMAINDER OF THE
TRACKERS SHOW A TRACK GENERALLY EAST-NORTHEASTWARD THROUGH THE
REMAINDER OF THE FORECAST PERIOD. HOWEVER, THE GFS, NAVGEM, EGRR
AND ECMWF AND ITS ENSEMBLE MEAN HAVE AL SHOWN SIGNIFICANT CHANGES
SINCE THE PREVIOUS RUN, AND NOW ALL AGREE ON A SLOWER TRACK SOUTH
OF TOKYO THROUGH TAU 72. INTERESTINGLY, THE GFS AND UKMET ENSEMBLE
MEAN TRACKERS REMAIN CONSISTENT WITH THE PREVIOUS RUNS AND INDICATE
A FAST TRACK TO THE NORTHEAST, CONSISTENT WITH THE PREVIOUS
FORECAST. WHILE THERE IS HIGH CONFIDENCE IN THE 0-24HR FORECAST
TRACK, WITH SUCH A HIGH DEGREE OF UNCERTAINTY IN THE DETERMINISTIC
GUIDANCE BEYOND TAU 36 AND THE EXTREMELY LARGE SPREAD IN THE
ENSEMBLE GUIDANCE, THERE IS OVERALL LOW CONFIDENCE IN THE JTWC
FORECAST TRACK. INTENSITY GUIDANCE IS IN OVERALL GOOD AGREEMENT,
THOUGH THE HWRF REMAINS UNREALISTICALLY HIGH AS IT JUMPS
CIRCULATIONS. THE REMAINDER OF THE GUIDANCE REMAINS TIGHTLY
CLUSTERED ABOUT THE CONSENSUS MEAN. THE JTWC FORECAST LIES SLIGHTLY
HIGHER THAN THE MEAN WITH MEDIUM CONFIDENCE DUE TO THE
UNCERTAINTIES ASSOCIATED WITH THE EXACT TRACK AND THUS THE AMOUNT
OF TERRAIN INTERACTION.  

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