Advisories

WDPN33 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 33.0N 154.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 793 NM EAST-SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC), WITH THE WESTERN 
PERIPHERY OF THE SYSTEM OBSCURED BY A POCKET OF DEEP CONVECTION AND
ASSOCIATED CIRRUS BLOWOFF, AND THE EASTERN SEMICIRCLE FULLY EXPOSED. 
ANIMATED TOTAL PRECIPITABLE WATER (TPW) IMAGERY, AS WELL AS A 080656Z 
SSMIS 91GHZ MICROWAVE IMAGE, REVEAL A LARGE WEDGE OF EXTREMELY DRY 
MID-LEVEL AIR ENTRAINED ALONG THE EASTERN FLANK. ANIMATED WATER VAPOR 
IMAGERY AND ATMOSPHERIC MOTION VECTOR (AMV) DATA VERIFY THE PRESENCE 
OF AN UPPER-LEVEL LOW POSITIONED JUST SOUTHWEST OF THE SURFACE LLCC, 
USHERING IN THE DRY MID-LEVEL AIR WHILE INDUCING CONVERGENCE ALOFT 
OVER THE SOUTHEASTERN PORTION OF TS 14W. THE INITIAL POSITION IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE MSI. 
THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON A 
BLEND OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED 
BELOW. THE ENVIRONMENT IS MARGINAL FOR INTENSIFICATION. SSTS ARE 
GENERALLY SUFFICIENT TO SUPPORT DEVELOPMENT, WHILE DEEP-LAYER SHEAR 
IS LOW. HOWEVER, THE PRESENCE OF THE UPPER-LEVEL LOW IN CLOSE 
PROXIMITY AND THE ASSOCIATED DRY AIR ENTRAINMENT AND UPPER 
CONVERGENCE ARE OFFSETTING THE OTHERWISE FAVORABLE FACTORS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF THE MID-LEVEL
SUBTROPICAL RIDGE (STR) CENTERED SOUTHWEST OF THE ALEUTIANS. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS SATCON: 40 KTS AT 080510Z
   CIMSS ADT: 35 KTS AT 080600Z
   CIMSS AIDT: 34 KTS AT 080600Z
   CIMSS D-MINT: 35 KTS AT 080656Z
   CIMSS D-PRINT: 33 KTS AT 080710Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK RADIAL
   OTHER FACTORS: UPPER-LEVEL LOW POSITIONED TO THE SOUTHWEST;
CONVERGENCE ALOFT; DRY AIR ENTRAINMENT. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 14W WILL CONTINUE TO TRACK
WESTWARD ALONG THE SOUTHERN FLANK OF A LOW- TO MID-LEVEL STR FOR
THE NEXT 12 TO 24 HOURS. THE SYSTEM WILL BEGIN TO DECELERATE AFTER
TAU 12, AS THE RIDGE BEGINS TO ERODE FROM THE WEST DUE TO AN
APPROACHING UPPER-LEVEL TROUGH MOVING EAST FROM JAPAN. AFTER TAU
24, THE SYSTEM SLOWS DOWN TO 5-6 KNOTS WHILE TURNING NORTHWESTWARD
AS A WEAKNESS DEVELOPS IN THE RIDGE OVER HOKKAIDO, WITH THE RIDGE
REORIENTING ALONG A NORTHWEST-TO-SOUTHEAST AXIS. BY TAU 72, THE 
TROUGH AND ASSOCIATED WEAKNESS IN THE RIDGE MOVE EAST AND ARE 
REPLACED BY A NEW RIDGE DEVELOPING OVER FAR EASTERN RUSSIA, WHICH 
WILL DRIVE TS 14W ONTO A WESTWARD TRACK ACROSS THE NORTHERN PORTION 
OF HONSHU. LANDFALL ALONG THE COAST OF HONSHU, IN THE GENERAL 
VICINITY OF SENDAI, JAPAN, IS EXPECTED NEAR TAU 72. THEREAFTER, THE 
SYSTEM RAPIDLY MOVES INTO THE SEA OF JAPAN (SOJ) ALONG THE STRONG 
GRADIENT ON THE SOUTHERN SIDE OF THE BUILDING RIDGE OVER EASTERN 
RUSSIA. AS THE SYSTEM WEAKENS AND SHALLOWS OUT IN THE EXTENDED 
FORECAST, THE STEERING GRADIENT WEAKENS, ALLOWING THE SYSTEM TO 
DECELERATE THROUGH TAU 120. REGARDING INTENSITY, TS 14W WILL FACE 
MARGINAL TO MARGINALLY UNFAVORABLE CONDITIONS FOR THE NEXT 12 TO 24 
HOURS, AS IT MOVES NORTHWESTWARD GENERALLY IN ALIGNMENT WITH THE 
UPPER-LEVEL LOW. AROUND TAU 24, THE UPPER LOW OPENS UP INTO A TROUGH 
AND BEGINS TO DECOUPLE FROM TS 14W, ALLOWING FOR MODEST IMPROVEMENT 
IN THE OVERALL ENVIRONMENT. BY TAU 48, ANOTHER UPPER-LEVEL LOW 
DEVELOPS NEAR SENDAI, WITH A TROUGH EXTENDING SOUTHEASTWARD TO THE 
SOUTH OF TS 14W, OPENING UP A ROBUST, NEAR-JET-LEVEL POLEWARD OUTFLOW
CHANNEL. TS 14W WILL TAP INTO THIS OUTFLOW CHANNEL AND INTENSIFY TO A 
PEAK OF 50 KNOTS BY TAU 60. FURTHER EVOLUTION OF THE UPPER-LEVEL 
PATTERN PLACES TS 14W ON THE NORTHWESTERN (CONVERGENT) SIDE OF THE 
UPPER LOW BY TAU 72, AND THE SYSTEM WILL WEAKEN SLIGHTLY AS IT 
APPROACHES LANDFALL. THE SYSTEM WILL BEGIN A RAPID SUBTROPICAL 
TRANSITION (STT) AS IT CROSSES HONSHU AND MOVES INTO THE SOJ, 
COMPLETING STT NO LATER THAN TAU 120. THE SYSTEM WILL STEADILY WEAKEN 
AS IT UNDERGOES STT. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN OVERALL GOOD AGREEMENT ON
THE TRACK SCENARIO. ALL GUIDANCE POINTS TO A WESTWARD TRACK THROUGH
TAU 24, FOLLOWED BY A NORTHWESTWARD TRAJECTORY THROUGH LANDFALL AT
TAU 72. CROSS-TRACK SPREAD GRADUALLY INCREASES TO 250NM AT TAU 72,
WITH GALWEM POSITIONED ON THE NORTHERN EDGE OF THE ENVELOPE AND
THE ECMWF ON THE SOUTHERN FLANK. THE ECMWF IS A SIGNIFICANT SOUTHERN 
OUTLIER, TRACKING THE SYSTEM OVER THE VICINITY OF IWAKI, DISPLACED 
NEARLY 100NM FROM THE PRIMARY MODEL CLUSTER. ENSEMBLE GUIDANCE 
DEPICTS A FAIRLY SIGNIFICANT AMOUNT OF UNCERTAINTY THROUGH TAU 72, 
WITH MEMBER DISPERSION EXTENDING FROM HOKKAIDO IN THE NORTH TO SOUTH 
OF TOKYO IN THE SOUTH. THE JTWC FORECAST IS PLACED NEAR THE
EXPERIMENTAL AI CONSENSUS MEAN WITH MEDIUM CONFIDENCE, DECREASED
DUE TO THE LARGE ENSEMBLE MEMBER DISPERSION. IN THE EXTENDED RANGE,
BOTH THE CONSENSUS PACKAGE AND THE SUPER ENSEMBLE SHOW INCREASED
SPREAD AND DISPERSION, LENDING LOW CONFIDENCE TO THE JTWC FORECAST
TRACK, WHICH IS POSITIONED NEAR THE AI CONSENSUS MEAN. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT OVERALL. HOWEVER, THE JTWC FORECAST
IS PLACED LOWER THAN ALL THE GUIDANCE SAVE FOR GOOGLE DEEPMIND
THROUGH TAU 36, BEFORE JOINING THE CONSENSUS ENVELOPE (WHICH PEAKS
AT 50 KNOTS AT TAU 60) THROUGH THE REMAINDER OF THE FORECAST. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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