Advisories

WDPN31 PGTW 280900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 30W (IN-FA) WARNING NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.1N 158.9E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 818 NM EAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RELATIVELY 
COMPACT SYSTEM CHARACTERIZED BY A 40 NM WIDE EYE AND A SYMMETRIC, 
COLD, CENTRAL DENSE OVERCAST (CDO). THE WIDE EYE EXHIBITS A 
WAVENUMBER-3 ASYMMETRY, WITH THREE MESOVORTICES ROTATING ALONG THE 
INTERIOR OF THE EYEWALL, WHICH DISPLAYS A PRONOUNCED STADIUM EFFECT. 
A 280526Z SSMIS 89 GHZ MICROWAVE IMAGE REVEALED A UNIFORM, 
CONVECTIVELY ROBUST EYEWALL WITH AN ABSENCE OF PROMINENT SPIRAL 
BANDING FEATURES. BASED ON THESE STRUCTURAL CHARACTERISTICS, SUPER 
TYPHOON (STY) 30W IS ASSESSED AS AN ANNULAR TYPHOON. IN THE UPPER-
LEVELS, THE SYNOPTIC ENVIRONMENT IS DOMINATED BY DEEP EASTERLY FLOW, 
WHICH IS IMPARTING STEADY EASTERLY VERTICAL WIND SHEAR (VWS). 
HOWEVER, A ROBUST UPPER-TROPOSPHERIC ANTICYCLONE DIRECTLY OVERLAYING 
STY 30W IS PROVIDING VIGOROUS RADIAL OUTFLOW ALOFT, EFFECTIVELY 
INSULATING THE INNER CORE AND REDUCING LOCAL VWS TO LESS THAN 10 
KNOTS. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON 
THE WELL-DEFINED EYE IN BOTH MICROWAVE IMAGERY AND MSI. THE INITIAL 
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON A BLEND OF THE 
OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES OUTLINED BELOW. 
ENVIRONMENTAL CONDITIONS REMAIN HIGHLY FAVORABLE, CHARACTERIZED BY 
LOW INNER-CORE SHEAR, HIGH SEA SURFACE TEMPERATURES (SSTS), MODERATE 
TO HIGH OCEAN HEAT CONTENT (OHC), AND STRONG RADIAL OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.5 - 127 KTS
   CIMSS SATCON: 135 KTS AT 280400Z
   CIMSS ADT: 117 KTS AT 280530Z
   CIMSS AIDT: 130 KTS AT 280530Z
   CIMSS D-MINT: 129 KTS AT 280526Z
   CIMSS D-PRINT: 137 KTS AT 280600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: SYSTEM IS CLASSIFIED AS AN ANNULAR TYPHOON. 

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: STY 30W HAS TRANSITIONED TO A WESTWARD TRACK 
FOLLOWING THE DISSIPATION OF THE NEAR-EQUATORIAL RIDGE (NER) TO THE 
SOUTHEAST. NOW FIRMLY UNDER THE STEERING INFLUENCE OF THE STR TO THE 
NORTH-NORTHEAST, STY 30W IS FORECAST TO ACCELERATE NORTHWESTWARD 
THROUGH TAU 36, WHEN IT WILL REACH A PEAK TRANSLATIONAL SPEED OF 17 
KTS. BY TAU 60, THE STR TO THE NORTHEAST WILL PROPAGATE EASTWARD, 
WHILE A SECONDARY RIDGE OVER EASTERN CHINA BUILDS EASTWARD. BETWEEN 
THE TWO RIDGES, A COL WILL BEGIN TO DEVELOP IN RESPONSE TO A PASSING 
MID-LATITUDE TROUGH. BY TAU 72, STY 30W WILL DECELERATE AS IT ENTERS 
THE SOUTHERN PORTION OF THE COL. BY TAU 96, THE SYSTEM WILL BECOME 
QUASI-STATIONARY WITHIN THE WEAK STEERING ENVIRONMENT BETWEEN THE 
STRENGTHENING RIDGES TO THE EAST AND WEST. HOWEVER, THIS QUASI-
STATIONARY PERIOD IS EXPECTED TO BE TRANSIENT AS THE STR TO THE EAST 
PROPAGATES EASTWARD AND ERODES, WHILE THE WESTERN RIDGE CONTINUES TO 
BUILD EASTWARD. THIS SYNOPTIC EVOLUTION WILL STRENGTHEN THE STEERING 
GRADIENT ON THE NORTHWESTERN FLANK OF STY 30W, DEFLECTING IT WEST-
SOUTHWESTWARD AFTER TAU 96. REGARDING INTENSITY, AS AN ANNULAR 
SYSTEM, STY 30W EXHIBITS ENHANCED STRUCTURAL STABILITY AND IS LESS 
SUSCEPTIBLE TO ADVERSE ENVIRONMENTAL FORCING, MAKING RAPID INTENSITY 
FLUCTUATIONS UNLIKELY. CONSEQUENTLY, STEADY-STATE INTENSITY IS 
FORECAST FOR THE NEXT 36 TO 48 HOURS. AROUND TAU 60, DYNAMICAL 
GUIDANCE, INCLUDING HAFS-A AND HWRF, INDICATES A DEGRADATION OF THE 
ANNULAR STRUCTURE FOLLOWED BY THE ONSET OF AN EYEWALL REPLACEMENT 
CYCLE (ERC) BY TAU 72, WHICH WILL INDUCE MODERATE WEAKENING. 
ADDITIONAL WEAKENING IS EXPECTED AS THE SYSTEM BECOMES QUASI-
STATIONARY OVER AN AREA OF RELATIVELY LOW OHC, RESULTING IN UPWELLING 
OF SIGNIFICANTLY COOLER SUBSURFACE WATERS. HOWEVER, WHILE POSITIONED 
WITHIN THE COL, THE CYCLONE WILL TAP INTO AN ENHANCED POLEWARD 
OUTFLOW CHANNEL ALOFT, WHICH SHOULD PARTIALLY MITIGATE OCEANIC 
COOLING EFFECTS, PARTICULARLY AS THE SYSTEM ACCELERATES WESTWARD AND 
EXITS THE UPWELLED COLD WAKE AFTER TAU 96.

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN 
STRONG AGREEMENT THROUGH THE MAJORITY OF THE FORECAST PERIOD, WITH 
NOTABLE CONVERGENCE IN THE EXTENDED RANGE. BY TAU 72, CROSS-TRACK 
SPREAD REMAINS CONSTRAINED AT 85 NM, WITH AI MODELS ON THE SOUTHERN 
BOUNDARY OF THE GUIDANCE ENVELOPE AND THE GFS, GEFS, AND ECMWF 
ENSEMBLE MEAN ON THE NORTHERN BOUNDARY. THROUGH TAU 96, THE GUIDANCE 
REMAINS TIGHTLY CLUSTERED, UNANIMOUSLY DEPICTING A SLOW NORTHWESTWARD 
PROGRESSION. BY TAU 120, THE ENVELOPE DIVERGES, BUT ALL CONSENSUS 
MEMBERS AGREE THAT THE SYSTEM WILL DEFLECT WESTWARD AFTER TAU 96. 
CROSS-TRACK SPREAD INCREASES TO 185 NM AT TAU 120, BOUNDED BY THE 
EGRR AND ECMWF ON THE SOUTHERN EDGE, AND THE GEFS MEAN AND NAVGEM ON 
THE NORTHERN EDGE. THE AI MODELS ARE CLUSTERED WITHIN THE NORTHERN 
HALF OF THE TRACK ENVELOPE, POLEWARD OF THE MULTI-MODEL CONSENSUS 
MEAN. ENSEMBLE GUIDANCE DEMONSTRATES STRONG AGREEMENT AMONG THE 
ENSEMBLE MEANS, WITH ALL MAJOR SUITES DEPICTING A NORTHWARD TURN 
AFTER TAU 72, AN INFLECTION POINT AT TAU 96, AND A SHARP WESTWARD 
RECURVATURE THROUGH TAU 120. HOWEVER, INTRA-ENSEMBLE DISPERSION 
REMAINS HIGH DESPITE THE CLOSE ALIGNMENT OF THE MEANS. THE OFFICIAL 
JTWC FORECAST TRACK IS POSITIONED NEAR THE AI CONSENSUS MEAN THROUGH 
THE FORECAST PERIOD. INTENSITY GUIDANCE IS IN GENERALLY GOOD 
AGREEMENT, WITH CONSENSUS MEMBERS INDICATING GRADUAL WEAKENING FROM 
TAU 12 ONWARDS. THE NOTABLE OUTLIERS ARE THE OPERATIONAL AND 
EXPERIMENTAL GOOGLE DEEPMIND (GDM) MODELS, WHICH MAINTAIN PEAK 
INTENSITY FOR A LONGER DURATION. GIVEN THE ANNULAR MORPHOLOGY OF THE 
SYSTEM, THE GDM SOLUTIONS ARE ASSESSED AS MORE REPRESENTATIVE, AS 
CONVENTIONAL DYNAMICAL MODELS TYPICALLY ERODE ANNULAR SYSTEMS 
PREMATURELY. THE JTWC INTENSITY FORECAST CLOSELY FOLLOWS THE GDM 
GUIDANCE THROUGH TAU 72, THEN BLENDS TOWARD THE CTCX AND HWRF 
SOLUTIONS THROUGH TAU 120.  

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