Advisories

WDPN31 PGTW 020900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 040//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.6N 140.9E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 134 NM SOUTH OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND SHORTWAVE INFRARED 
(SWIR) IMAGERY DEPICT A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION 
CENTER (LLCC), WITH FRAGMENTED DEEP CONVECTIVE BANDS WRAPPING INTO 
THE LLCC ALONG THE SOUTHEASTERN THROUGH NORTHERN QUADRANTS. A 020347Z 
ATMS 89-GHZ MICROWAVE PASS REVEALED A WELL-DEFINED MICROWAVE EYE 
FEATURE WITH NASCENT CONVECTIVE CELLS DEVELOPING TO THE EAST AND 
NORTHWEST OF THE VORTEX CENTER. SYNOPTICALLY, A BAROCLINIC COLD-
FRONTAL BOUNDARY PROPAGATING SOUTH OF JAPAN IS POSITIONED 
APPROXIMATELY 560 NM TO THE NORTHWEST OF TYPHOON (TY) 30W AND WILL 
MODULATE THE SUBSEQUENT TRACK AND EXTRATROPICAL EVOLUTION. IN THE 
UPPER LEVELS, UPPER-TROPOSPHERIC VENTILATION HAS DIMINISHED RELATIVE 
TO 24 HOURS AGO, AS THE SYSTEM HAS DECOUPLED FROM THE STRONG 
EQUATORWARD OUTFLOW CHANNEL AND POLEWARD OUTFLOW HAS SIMILARLY 
WEAKENED IN RESPONSE TO SLIGHT WEAKENING OF THE ANTICYCLONE TO THE 
EAST. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON 
THE PARTIALLY EXPOSED LLCC IN THE MSI AND SWIR IMAGERY. ULTRA-HIGH 
RESOLUTION (UHR) ANALYSIS OF THE 012345Z ASCAT-C PASS REVEALED PEAK 
SURFACE WINDS OF 75 KTS TO THE NORTH OF THE LLCC, PROMPTING A 
REANALYSIS UPGRADE OF THE 0000Z INTENSITY TO 75 KTS. THIS REANALYSIS 
ALSO PROVIDED HIGH CONFIDENCE IN THE INITIAL INTENSITY OF 70 KTS, 
WHICH IS WEIGHTED ABOVE THE DVORAK-BASED ESTIMATES THAT ARE 
UNDERESTIMATING THE TRUE VORTEX INTENSITY DUE TO DISORGANIZED CENTRAL 
CONVECTION. ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE AND 
IMPROVING NOW THAT THE SYSTEM HAS EMERGED FROM ITS UPWELLED COLD 
WAKE. DEEP-LAYER VERTICAL WIND SHEAR (VWS) REMAINS LOW, SEA SURFACE 
TEMPERATURES (SSTS) ARE INCREASING, AND UPPER-LEVEL OUTFLOW REMAINS 
SUPPORTIVE, THOUGH ELEVATED MID-LEVEL SHEAR CONTINUES TO EXERT AN 
INHIBITING EFFECT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: TY 30W IS EMBEDDED IN A WEAK STEERING 
PATTERN WITHIN A COL REGION BETWEEN TWO SUBTROPICAL RIDGES (STR) TO 
THE EAST AND WEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS SATCON: 74 KTS AT 020347Z
   CIMSS ADT: 57 KTS AT 020530Z
   CIMSS AIDT: 56 KTS AT 020530Z
   CIMSS D-PRINT: 55 KTS AT 020600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: MODERATE NORTHWESTERLY MID-LEVEL SHEAR. 

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: TY 30W IS TRACKING SLOWLY WEST-NORTHWESTWARD. 
WHILE THE SYSTEM REMAINS EMBEDDED WITHIN THE COL REGION, THE BROADER 
SYNOPTIC-SCALE RIDGE COMPLEX IS RETROGRADING WESTWARD, ADVECTING TY 
30W ALONG WITH IT. OVER THE NEXT 24 HOURS, A SERIES OF TRANSIENT MID-
LATITUDE SHORTWAVE TROUGHS WILL PROPAGATE TO THE NORTH, ERODING THE 
NORTHEASTERN PERIPHERY OF THE WESTERN STR. SIMULTANEOUSLY, THE 
WESTERN PERIPHERY OF THE EASTERN STR WILL REORIENT ALONG A MORE 
MERIDIONAL (NORTH-SOUTH) AXIS. IN RESPONSE TO THESE SYNOPTIC STEERING 
MODIFICATIONS, TY 30W WILL RECURVE POLEWARD AFTER TAU 36, CREST THE 
RIDGE AXIS BY TAU 48, AND BEGIN TO ACCELERATE NORTHEASTWARD 
THEREAFTER. TY 30W WILL INTERACT WITH THE REMNANT COLD-FRONTAL 
BOUNDARY, CURRENTLY POSITIONED FAR TO THE NORTHWEST, NEAR TAU 48, 
WHICH WILL ENHANCE ITS NORTHEASTWARD RECURVATURE. AFTER TAU 60, TY 
30W WILL RAPIDLY ACCELERATE NORTHEASTWARD AS IT BEGINS TO EMBED 
WITHIN THE MID-LATITUDE WESTERLIES. THE SYSTEM WILL INITIATE 
EXTRATROPICAL TRANSITION (ETT) BY TAU 72 AS IT PHASES WITH THE 
AMPLIFYING MID-LATITUDE TROUGH. REGARDING INTENSITY, TY 30W HAS 
LIKELY REACHED ITS NEAR-TERM INTENSITY NADIR; AS IT TRAVERSES MORE 
CLIMATOLOGICALLY TYPICAL SSTS OF 28-29 CELSIUS, IT SHOULD BEGIN TO 
GRADUALLY RE-INTENSIFY AFTER TAU 12. THE SYSTEM WILL EXPERIENCE A 24- 
TO 36-HOUR WINDOW OF SUPPORTIVE THERMODYNAMIC AND DYNAMIC CONDITIONS 
FOR RE-INTENSIFICATION BEFORE RAPIDLY INCREASING VWS AND DRY AIR 
ENTRAINMENT INDUCE STEADY WEAKENING. BY TAU 72, THE VORTEX WILL 
ENCOUNTER STRONG DEEP-LAYER VWS AND DRY AIR INTRUSION WHILE CROSSING 
POLEWARD OF THE 26-CELSIUS ISOTHERM; HOWEVER, THE RATE OF SPIN-DOWN 
WILL BE PARTIALLY MITIGATED BY NON-TROPICAL BAROCLINIC FORCING AND 
VIGOROUS DIVERGENCE ALOFT WITHIN THE EQUATORWARD ENTRANCE REGION OF A 
ROBUST UPPER-TROPOSPHERIC JET STREAK. TY 30W IS FORECAST TO COMPLETE 
ETT BY TAU 96 AS A STORM-FORCE EXTRATROPICAL CYCLONE FAR TO THE EAST 
OF MISAWA, JAPAN 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD OVERALL AGREEMENT, WITH 
TWO NOTABLE OUTLIERS. THE UKMET ENSEMBLE (UKEP) IS THE NEAR-TERM 
OUTLIER, ADVECTING THE SYSTEM TOO FAR WEST PRIOR TO NORTHEASTWARD 
RECURVATURE. GALWEM IS THE EXTENDED-RANGE OUTLIER, TRACKING THE 
SYSTEM NORTH-NORTHEASTWARD ALONG A TRAJECTORY SIGNIFICANTLY CLOSER TO 
NORTHERN HONSHU THAN ANY OTHER GUIDANCE MEMBER. EXCLUDING THESE TWO 
OUTLIERS, THE REMAINDER OF THE MULTI-MODEL TRACK CONSENSUS IS TIGHTLY 
CLUSTERED WITHIN A 55-NM ENVELOPE AT TAU 72. HOWEVER, BY TAU 72, 
ALONG-TRACK PHASE UNCERTAINTY BEGINS TO AMPLIFY BETWEEN THE FASTER AI 
MODELS AND THE SLOWER DYNAMICAL (PHYSICS-BASED) MODELS. BY TAU 96, 
CROSS-TRACK DISPERSION INCREASES MODERATELY TO 140 NM, BOUNDED BY THE 
DETERMINISTIC ECMWF AND EPS ENSEMBLE MEAN ON THE EASTERN PERIPHERY, 
AND THE UKMET (EGRR) AND AI CONSENSUS (AICN) ON THE WESTERN 
PERIPHERY. ALONG-TRACK SPREAD DIVERGES SHARPLY AS GUIDANCE BIFURCATES 
REGARDING POST-RECURVATURE TRANSLATION SPEED WITHIN THE MID-LATITUDE 
WESTERLIES. THE SLOWEST OF THE DYNAMICAL MODELS IS NAVGEM, WHILE THE 
FASTEST OF THE AI MODELS REMAINS THE EC-AIFS. THE GFS, AICN, AND 
GOOGLE DEEPMIND (GDM) CLUSTER CLOSELY WITH THE EC-AIFS, WHILE THE 
DETERMINISTIC ECMWF, MULTI-MODEL CONSENSUS MEAN, WINDBORNE, AND GEFS 
MEAN ARE CLUSTERED APPROXIMATELY MIDWAY BETWEEN THE NAVGEM AND EC-
AIFS EXTREMES. THE OFFICIAL JTWC TRACK FORECAST IS POSITIONED NEAR 
THE SELECTIVELY FILTERED CONSENSUS (TES1) MEAN THROUGH THE FORECAST 
PERIOD. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL 
INTENSITY EVOLUTION, INDICATING SECONDARY PEAK INTENSITIES BETWEEN 75 
AND 90 KTS. THE OFFICIAL JTWC INTENSITY FORECAST CLOSELY TRACKS THE 
CTCX SOLUTION THROUGH THE FORECAST PERIOD. 

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