Advisories

WDPN33 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING 
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.3N 150.7E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 668 NM SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY 
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC), DEVOID OF SIGNIFICANT 
DEEP CONVECTION. TRACK MOTION HAS BECOME INCREASINGLY ERRATIC OVER 
THE PAST SIX HOURS DUE TO THE SYSTEM BEING CURRENTLY POSITIONED IN A 
WEAK AND COMPETING STEERING PATTERN DEFINED BY STRONG SUBTROPICAL 
RIDGING TO THE NORTHEAST AND SOUTHWEST, AND A COL WEAKNESS IN THE 
RIDGE TO THE NORTHWEST OVER HOKKAIDO. OVER THE LAST 1-2 HOURS, THE 
LLCC HAS BEGUN A COUNTERCLOCKWISE LOOP WHILE REMAINING QUASI-
STATIONARY. ANIMATED WATER VAPOR IMAGERY, ATMOSPHERIC MOTION VECTORS 
(AMV), AND MODEL ANALYSIS FIELDS DEPICT A COMPLEX UPPER-LEVEL LOW 
(ULL) CENTERED JUST NORTH OF THE LLCC WITH A TROUGH EXTENDING TO THE 
SOUTHEAST. THE PROXIMITY OF THE ULL TO THE NORTH CREATES AN 
UNFAVORABLE ENVIRONMENT FOR TS 14W, INDUCING CONVERGENT NORTHWESTERLY 
SUBSIDENT FLOW AND SIGNIFICANT DRY AIR ENTRAINMENT OVER THE CORE. 
PHASE CLASSIFICATION WORKSHEETS INDICATE THE SYSTEM IS A HYBRID OR 
BORDERLINE SUBTROPICAL CYCLONE AT THIS TIME, EXHIBITING 
CHARACTERISTICS OF BOTH A TROPICAL AND SUBTROPICAL CYCLONE. UPSTREAM, 
JUST EAST OF JAPAN, WATER VAPOR IMAGERY DEPICTS A LARGE UPPER-LEVEL 
DEFORMATION ZONE AND A DEEP TROUGH MOVING RAPIDLY INTO THE NORTHERN 
SEA OF JAPAN (SOJ), BOTH OF WHICH WILL HAVE A SIGNIFICANT IMPACT ON 
THE FUTURE EVOLUTION 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 MEDIUM CONFIDENCE, BASED PRIMARILY ON THE 
CIMSS SATCON ESTIMATE AND PERSISTENCE WITH EARLIER SCATTEROMETER 
DATA. THE ENVIRONMENT IS MARGINALLY UNFAVORABLE WITH UNFAVORABLE 
UPPER-LEVEL CONDITIONS OFFSETTING OTHERWISE FAVORABLE PARAMETERS 
(WARM SEA SURFACE TEMPERATURES AND LOW VERTICAL WIND SHEAR).

INITIAL WIND RADII BASIS: PERSISTENCE. 

CURRENT STEERING MECHANISM: COMPETING AND WEAK STEERING PATTERN,
INCREASINGLY DOMINATED BY THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) CENTERED SOUTHWEST OF THE WESTERN ALEUTIANS. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS SATCON: 40 KTS AT 090440Z
   CIMSS ADT: 25 KTS AT 090600Z
   CIMSS AIDT: 27 KTS AT 090600Z
   CIMSS D-MINT: 33 KTS AT 090603Z
   CIMSS D-PRINT: 31 KTS AT 090640Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK EASTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: GLOBAL MODELS AGREE THAT TS 14W WILL REMAIN
TRAPPED IN A COMPETING STEERING PATTERN FOR ANOTHER FEW HOURS AND 
REMAIN QUASI-STATIONARY. BY TAU 12, HOWEVER, ALL MAJOR GLOBAL MODELS
DEPICT A RAPID CHANGE IN THE UPPER-LEVEL PATTERN, WITH THE STR TO
THE NORTHEAST BUILDING QUICKLY AND EXTENDING NORTHWESTWARD,
SUPPLANTING THE RIDGE WEAKNESS CURRENTLY POSITIONED OVER HOKKAIDO. 
ONCE THIS OCCURS, TS 14W WILL EJECT FROM ITS QUASI-STATIONARY 
POSITION AND ACCELERATE NORTHWESTWARD. BY TAU 36, RIDGING OVER KOREA 
IS FORECAST TO RAPIDLY BUILD AND EXTEND NORTHEASTWARD, ULTIMATELY 
BRIDGING WITH THE RIDGE SOUTHEAST OF KAMCHATKA. THIS WILL DRIVE TS 
14W WESTWARD AFTER TAU 48. LANDFALL ON THE EASTERN COAST OF HONSHU IS 
EXPECTED SHORTLY AFTER TAU 48, AS THE SYSTEM TRACKS QUICKLY WESTWARD 
ALONG THE SOUTHERN FLANK OF THE MID-LEVEL STR TO THE NORTH. THE 
SYSTEM EMERGES INTO THE SOJ BY TAU 60, BUT BEGINS TO DECELERATE AFTER 
TAU 72 AS IT SHALLOWS AND MOVES INTO A WEAKER STEERING PATTERN. IN 
TERMS OF INTENSITY, THE KEY FACTOR WILL BE THE PROXIMITY AND 
ORIENTATION TO A SERIES OF UPPER-LEVEL LOWS (ULL). THE CURRENT ULL IS 
POSITIONED IN AN UNFAVORABLE SUBSIDENT QUADRANT NORTH OF TS 14W. OVER 
THE NEXT 18-24 HOURS, THE ULL IS EXPECTED TO FILL AND MOVE SLIGHTLY 
NORTHWARD, WHICH WILL INHIBIT SIGNIFICANT INTENSIFICATION. AROUND TAU 
24, THE DEEP TROUGH CURRENTLY CUTTING ACROSS THE NORTHERN SOJ WILL 
CUT OFF INTO AN ISOLATED ULL, WHICH WILL DIVE SOUTHWARD ALONG THE 
EASTERN COAST OF HONSHU TO A POSITION WEST OF TS 14W. THIS WILL OPEN 
UP A ROBUST POLEWARD OUTFLOW CHANNEL COINCIDENT WITH TS 14W CROSSING 
THE AXIS OF THE WARM KUROSHIO CURRENT. THESE TWO FACTORS COMBINE TO 
ALLOW FOR A PERIOD OF MARKED INTENSIFICATION, UP TO A PEAK OF 50-55 
KNOTS BY TAU 36. HOWEVER, BY TAU 48, THE ULL WILL TRANSLATE SOUTH OF 
TS 14W, WHILE THE SYSTEM MOVES OVER THE COOLER WATERS OF THE OYASHIO 
CURRENT ALONG THE COAST. THESE NEGATIVE INFLUENCES WILL LEAD TO A 
GENERAL WEAKENING TREND AS THE SYSTEM APPROACHES LANDFALL. THE SYSTEM 
WILL RAPIDLY WEAKEN OVER LAND BEFORE EMERGING INTO THE SOJ AS A 
MINIMAL TROPICAL STORM, WHICH WILL BE IN THE EARLY PHASES OF 
SUBTROPICAL TRANSITION (STT). THE SYSTEM WILL COMPLETE STT BY TAU 72 
WHILE SIMULTANEOUSLY WEAKENING DUE TO INCREASED VWS AND DRY AIR 
ENTRAINMENT THROUGH THE REMAINDER OF THE FORECAST PERIOD. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT
THROUGH THE FORECAST PERIOD. ALL CONSENSUS MEMBERS DEPICT A SLOW,
QUASI-STATIONARY MOTION FOR THE FIRST FEW HOURS, FOLLOWED BY A
SHARP TURN NORTHWESTWARD BEFORE TAU 12, THEN A WESTWARD TURN BY TAU
48. THE JGSM AND GFS DETERMINISTIC TRACKERS ARE POSITIONED ON THE
NORTHERN EDGE OF THE GUIDANCE ENVELOPE, WHILE THE ECMWF AND
EXPERIMENTAL GOOGLE DEEPMIND ARE POSITIONED ON THE SOUTHERN EDGE.
CROSS-TRACK SPREAD INCREASES TO 100NM AT TAU 48, AND GRADUALLY
INCREASES TO 150NM AT TAU 96. ENSEMBLE GUIDANCE IS CONTINUING TO
TREND TOWARDS INCREASING UNCERTAINTY AND MEMBER DISPERSION. THE
ENSEMBLE MEMBER ENVELOPE OF THE EXPERIMENTAL JTWC SUPER ENSEMBLE
NOW STRETCHES FROM YOKOSUKA TO MISAWA AT LANDFALL, INCREASING TO A
RANGE FROM SASEBO TO THE DPRK-ROK BORDER BY THE END OF THE FORECAST
PERIOD. THE JTWC FORECAST IS POSITIONED CLOSE TO THE AI CONSENSUS
MEAN, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT, WITH ALL CONSENSUS MEMBERS CONFINED TO A TIGHT ENVELOPE
WHICH PEAKS BETWEEN 45-50 KNOTS AT TAU 36 FOLLOWED BY SHARP
WEAKENING THROUGH THE REMAINDER OF THE FORECAST. THE JTWC FORECAST
IS PLACED NEAR THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE. 

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