Advisories

WDPN33 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING 
NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 34.8N 148.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 448 NM EAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED, COMPACT AND IRREGULAR LOW LEVEL CIRCULATION CENTER (LLCC),
EXHIBITING SOME TROCHOIDAL MOTION AS IT ATTEMPTS TO MOVE UNDER 
FLARING CONVECTION TO THE NORTH. ANIMATED WATER VAPOR IMAGERY, 
ATMOSPHERIC MOTION VECTOR (AMV) ANALYSIS AND MODEL FIELDS DEPICT AN 
UPPER-LEVEL LOW (ULL) EAST OF SENDAI, JAPAN, WITH TROUGHING EXTENDING 
SOUTHEASTWARD OVER THE SOUTHERN PORTION OF TS 14W, PROVIDING 
DIVERGENT FLOW ALOFT OVER THE SYSTEM. A 100550Z SSMIS 91GHZ MICROWAVE 
IMAGE REVEALED VERY SHALLOW BANDING FEATURES ACROSS THE SOUTHERN 
SEMICIRCLE OF THE CIRCULATION, WHICH LIES UNDERNEATH AN UPPER-LEVEL 
TROUGH AXIS AND CONCOMITANT MID-LEVEL DRY AIR. DEEP CONVECTION IS 
BLOSSOMING ACROSS THE NORTHERN HALF OF THE CIRCULATION UNDER THE 
DIVERGENT UPPER-LEVEL FLOW, BUT SO FAR HAS FAILED TO WRAP INTO THE 
CORE OF THE SYSTEM. THE INITIAL POSITION IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE MSI AND MICROWAVE IMAGERY DISCUSSED ABOVE. 
THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, CONSISTENT 
WITH EARLIER SCATTEROMETER DATA AS WELL AS THE CIMSS ADT AND SATCON 
ESTIMATES. ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE, WITH 
ROBUST POLEWARD OUTFLOW AND WARM SSTS OFFSET BY MODERATE VERTICAL 
WIND SHEAR (VWS) AND DRY ENTRAINMENT ALONG THE SOUTHERN FLANK OF THE 
CIRCULATION.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS SATCON: 40 KTS AT 100510Z
   CIMSS ADT: 41 KTS AT 100600Z
   CIMSS AIDT: 31 KTS AT 100600Z
   CIMSS D-MINT: 31 KTS AT 100550Z
   CIMSS D-PRINT: 40 KTS AT 100600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR DRAPED ACROSS THE SOUTHERN HALF
OF THE SYSTEM IN CONJUNCTION WITH UPPER-LEVEL TROUGH. 

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 WILL CONTINUE TRACKING
NORTHWESTWARD FOR THE NEXT 12 HOURS, ALONG THE SOUTHWESTERN FLANK
OF THE STR TO THE NORTHEAST. THE SYSTEM WILL REACH AN INFLECTION
POINT AND TURN WESTWARD AFTER TAU 12, AS A BUILDING RIDGE TO THE
NORTH TAKES OVER AS THE PRIMARY STEERING MECHANISM. LANDFALL ALONG
THE COAST OF HONSHU NORTHEAST OF TOKYO IS EXPECTED SHORTLY AFTER
TAU 24. THE SYSTEM THEN TRAVERSES WEST THROUGH CENTRAL HONSHU BEFORE 
SKIRTING THE NORTHWESTERN COAST OF HONSHU, POTENTIALLY MOVING INTO 
THE FAR SOUTHERN REACHES OF THE SEA OF JAPAN (SOJ) THROUGH TAU 60. IN 
TERMS OF INTENSITY, THE SYSTEM IS EXPECTED TO INTENSIFY UP TO 50 
KNOTS WITHIN THE NEXT 12 HOURS, AS IT REMAINS IN THE DIVERGENT SECTOR 
OF THE ULL AND MOVES OVER THE KUROSHIO CURRENT. THE PEAK WILL BE 
SHORT-LIVED, HOWEVER. BY TAU 18, VWS WILL RAPIDLY INCREASE, SSTS WILL 
DROP DRAMATICALLY AS THE SYSTEM MOVES OVER THE OYASHIO CURRENT, AND 
CONVERGENT FLOW ALOFT WILL IMPACT THE SYSTEM, MARKING THE BEGINNING 
OF A WEAKENING PHASE PRIOR TO LANDFALL. THE SYSTEM RAPIDLY WEAKENS AS 
IT CROSSES HONSHU, WHILE BEGINNING SUBTROPICAL TRANSITION (STT). TS 
14W WILL DISSIPATE BY TAU 60 WHILE SIMULTANEOUSLY COMPLETING STT. 
SIGNIFICANT UNCERTAINTY SURROUNDS THE TRACK FORECAST AFTER LANDFALL, 
AS THE SYSTEM WILL BE SEVERELY DISRUPTED CROSSING THE JAPANESE ALPS, 
AND THE LOCALIZED TERRAIN WILL HAVE AN OUTSIZED IMPACT ON THE 
TRAJECTORY OF THE LLCC AS IT MOVES WESTWARD. DEVIATIONS AROUND 
TERRAIN FEATURES COULD RESULT IN THE SYSTEM REMAINING OVER LAND 
THROUGH THE FORECAST PERIOD OR ALTERNATIVELY, MOVING INTO THE SOJ 
EARLIER THAN CURRENTLY FORECAST.  

MODEL DISCUSSION: MODEL GUIDANCE CONTINUES TO DIVERGE, PARTICULARLY
AFTER TAU 24, WITH THE GUIDANCE PACKAGE NOW ROUGHLY EVENLY SPLIT
BETWEEN A WESTWARD TRAJECTORY AND A SOUTHWESTWARD COURSE WHICH
TAKES THE SYSTEM THROUGH THE TOKYO METRO AREA. THE GEFS, GFS, JGSM
AND UKMET MODELS MAKE UP THE WESTWARD TRACKING GROUP, WHILE THE
GOOGLE DEEPMIND, ECMWF, NAVGEM AND EC-AIFS COMPRISE THE
SOUTHWESTWARD TRACKING GROUP. THE AI CONSENSUS AND THE STANDARD
JTWC CONSENSUS MEAN, AS WELL AS THE EPS MEAN, ARE ROUGHLY IN THE
MIDDLE BETWEEN THE TWO GROUPINGS. ENSEMBLES CONTINUE TO TREND
SOUTHWARD AS WELL, WITH MEMBERS CONFINED TO AN ENVELOPE BETWEEN
SENDAI AND YOKOSUKA. THE JTWC FORECAST HAS SHIFTED SLIGHTLY SOUTH
SINCE THE PREVIOUS FORECAST AND IS PLACED NEAR THE AI CONSENSUS
MEAN, AND THE JTWC EXPERIMENTAL SUPER ENSEMBLE MEAN, WITH MEDIUM
CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM
WILL REACH A PEAK INTENSITY BETWEEN 45-50 KNOTS AT TAU 12, FOLLOWED
BY STEADY TO RAPID WEAKENING THROUGH THE REMAINDER OF THE FORECAST
PERIOD. 

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