Advisories

WDPN33 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 33.1N 153.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 723 NM EAST-SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN EXPOSED, 
COMPACT LOW LEVEL CIRCULATION CENTER (LLCC) WITH FLARING CONVECTION 
ALONG THE SOUTHERN FLANK, NOW RAPIDLY DISSIPATING AND PUSHING 
SOUTHWARD. A PARTIAL 081039Z ASCAT-C PASS DEPICTED A LARGE EXPANSE OF 
35-40 KNOT WINDS IN THE NORTHWESTERN QUADRANT, WRAPPING SOUTHWARD AND 
INTO THE SOUTHWESTERN QUADRANT. ANIMATED WATER VAPOR IMAGERY AND 
ATMOSPHERIC MOTION VECTOR (AMV) DATA SHOW AN ELONGATED UPPER-LEVEL LOW 
POSITIONED TO THE EAST AND SOUTHEAST OF THE LLCC. UPPER-LEVEL 
NORTHERLY FLOW IS GENERATING STRONG EQUATORWARD OUTFLOW ALONG THE 
WESTERN PERIPHERY OF THE SYSTEM, WHILE DRY AIR AND CONVERGENT FLOW ARE 
IMPACTING THE EASTERN PORTION OF TS 14W, AND WRAPPING INTO THE 
NORTHERN PORTION OF THE CIRCULATION. THE INITIAL POSITION IS ASSESSED 
WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE EIR. THE INITIAL 
INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, BASED ON A BLEND OF THE 
OBJECTIVE AND SUBJECTIVE ESTIMATES NOTED BELOW INFLUENCED BY THE 
AFOREMENTIONED SCATTEROMETER DATA. ENVIRONMENTAL CONDITIONS ARE 
MARGINALLY FAVORABLE, WITH LOW VERTICAL WIND SHEAR (AVERAGED OVER THE 
ENTIRE CIRCULATION), MODERATELY WARM SSTS AND GOOD EQUATORWARD OUTFLOW 
ALOFT. HOWEVER, THE PRESENCE OF THE UPPER-LEVEL LOW IN CLOSE PROXIMITY 
IS INTRODUCING DRY MID-LEVEL AIR AND CONVERGENT FLOW ALONG THE EASTERN 
FLANK OF THE CIRCULATION AND LOCALIZED SHEAR OVER THE LLCC IS HIGHER 
THAN THE AREA-AVERAGED VALUES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 39 KTS AT 080940Z
   CIMSS ADT: 35 KTS AT 081200Z
   CIMSS AIDT: 34 KTS AT 081200Z
   CIMSS D-MINT: 36 KTS AT 080852Z
   CIMSS D-PRINT: 34 KTS AT 081200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: UPPER-LEVEL LOW IN CLOSE PROXIMITY TO THE EAST. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 14W IS TRACKING DUE WESTWARD 
ALONG THE SOUTHERN PERIPHERY OF A MID-LEVEL STR CENTERED TO THE 
NORTHEAST. THIS MOTION IS FORECAST TO CONTINUE FOR THE NEXT 12 HOURS. 
THE SYSTEM WILL DECELERATE AFTER TAU 12 AS AN UPPER-LEVEL TROUGH MOVES 
EAST OF JAPAN AND ERODES THE WESTERN PORTION OF THE STR, DEVELOPING A 
WEAKNESS IN THE RIDGE SOUTHEAST OF HOKKAIDO WHILE SIMULTANEOUSLY, THE 
RIDGE REORIENTS TO A MORE NORTHWEST-SOUTHEAST AXIS. BETWEEN TAU 12 AND 
TAU 24, TS 14W WILL TURN SHARPLY NORTHWESTWARDS, ALONG THE 
SOUTHWESTERN FLANK OF THE STR AND GENERALLY TOWARDS THE WEAKNESS IN 
THE STEERING RIDGE EAST OF JAPAN. AFTER TAU 48, RIDGING IS FORECAST TO 
BUILD IN ACROSS NORTHERN JAPAN AND SAKHALIN ISLAND, CONNECTING WITH 
DEVELOPING RIDGING OVER KOREA. DEVELOPMENT OF THIS RIDGE WILL TURN TS 
14W WESTWARD AFTER TAU 60, WITH LANDFALL IN THE VICINITY OF SENDAI, 
JAPAN EXPECTED JUST PRIOR TO TAU 72. THE SYSTEM THEN ACCELERATES 
WESTWARD ALONG THE STRONG GRADIENT INTO THE SEA OF JAPAN (SOJ). BY THE 
END OF THE FORECAST PERIOD, AS THE SYSTEM WEAKENS AND SHALLOWS, IT 
COMES UNDER THE INFLUENCE OF THE WEAKER, LOWER-LEVEL FLOW AND SLOWS 
DRAMATICALLY AS IT APPROACHES THE EASTERN COAST OF SOUTH KOREA. IN 
TERMS OF INTENSITY, THE CLOSE PROXIMITY OF THE UPPER-LEVEL LOW WILL 
INHIBIT INTENSIFICATION FOR THE FIRST 24 HOURS OF THE FORECAST. AFTER 
TAU 36, THE UPPER LOW SHIFTS POSITION TO THE WEST OF TS 14W, OPENING 
UP A POLEWARD OUTFLOW CHANNEL WHICH WILL ALLOW THE SYSTEM TO QUICKLY 
INTENSIFY UP TO A PEAK OF 55 KNOTS. TS 14W WILL WEAKEN SLIGHTLY AS IT 
APPROACHES LANDFALL (TAU 60) AS THE UPPER-LEVEL LOW SHIFTS POSITION 
AGAIN AND MOVES TO THE SOUTHEAST OF TS 14W, INTRODUCING CONVERGENT 
NORTHERLY FLOW ALOFT. AFTER LANDFALL, THE SYSTEM WILL RAPIDLY WEAKEN 
AS IT CROSSES THE JAPANESE ALPS. ONCE THE SYSTEM MOVES INTO THE SOJ, 
IT WILL BEGIN A RAPID SUBTROPICAL TRANSITION (STT), BECOMING 
SUBTROPICAL BY TAU 96, WHILE STEADILY WEAKENING THROUGH THE REMAINDER 
OF THE FORECAST PERIOD. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN MODERATE AGREEMENT. CROSS-TRACK 
SPREAD INCREASES TO 225 NM BY TAU 72, WITH THE ECMWF CONTINUING TO 
MARK THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE, WHILE JGSM AND GALWEM 
MARK THE NORTHERN EDGE, TAKING THE SYSTEM OVER MISAWA. THROUGH TAU 
120, THE MODELS MAINTAIN THE SAME OVERALL ORIENTATION AND AMOUNT OF 
CROSS-TRACK SPREAD. ENSEMBLE GUIDANCE IS TIGHTLY CLUSTERED THROUGH TAU 
24, BUT THEN RAPIDLY DISPERSES INTO A VAST FAN, WITH INDIVIDUAL 
MEMBERS TRACKING AS FAR NORTH AS NORTHERN HOKKAIDO AND AS FAR SOUTH AS 
SOUTHERN KYUSHU, ALTHOUGH THE ENSEMBLE MEANS ARE IN FAIRLY TIGHT 
AGREEMENT ON A LANDFALL NEAR SENDAI. THE JTWC FORECAST IS PLACED NEAR 
THE MULTI-MODEL CONSENSUS MEAN, THOUGH CONFIDENCE IS REDUCED IN LIGHT 
OF THE LARGE AMOUNT OF ENSEMBLE DISPERSION. INTENSITY GUIDANCE IS IN 
GOOD AGREEMENT AND THE PEAK INTENSITY RANGES FROM 50-60 KNOTS BETWEEN 
TAU 48 AND TAU 60 ACROSS ALL MODELS. THE JTWC FORECAST IS POSITIONED 
CLOSE TO THE HAFS-A MODEL 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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