Advisories

WDPN31 PGTW 281500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 30W (IN-FA) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.4N 157.6E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 744 NM EAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 55 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THAT WHILE 
SUPER TYPHOON (STY) 30W HAS MAINTAINED A COMPACT CORE OF SYMMETRICAL 
DEEP CONVECTION SURROUNDING A 35-40 NM WIDE EYE, THE CENTRAL DENSE 
OVERCAST (CDO) HAS ERODED SIGNIFICANTLY IN THE NORTHEASTERN SECTOR 
OVER THE PAST SIX HOURS. THE SYSTEM RETAINS CHARACTERISTICS OF AN 
ANNULAR TROPICAL CYCLONE, ALBEIT WITH DEGRADED STRUCTURAL SYMMETRY 
COMPARED TO SIX HOURS AGO. A 281128Z AWS 89 GHZ MICROWAVE IMAGE 
REVEALED A COMPACT INNER CORE OF DEEP CONVECTION ORGANIZED IN AN 
ANNULAR RING AROUND THE EYE FEATURE. HOWEVER, CONSISTENT WITH THE EIR 
IMAGERY, THE NORTHEASTERN QUADRANT OF THE CONVECTIVE RING IS 
SIGNIFICANTLY MORE SHALLOW AND FRAGMENTED THAN THE REMAINING 
QUADRANTS. MODEL-DERIVED SOUNDINGS INDICATE THAT MODERATE MID-LEVEL 
(850-400 MB) EASTERLY VERTICAL WIND SHEAR (VWS) IS DRIVING THIS 
CONVECTIVE ASYMMETRY BY ENTRAINING DRY AIR INTO THE UPSHEAR-RIGHT 
QUADRANT. A 281036Z ASCAT-B PASS DEPICTED A NEARLY SYMMETRICAL 
SURFACE WIND FIELD, PROMPTING A SLIGHT EXPANSION OF THE INITIAL WIND 
RADII WITH HIGH CONFIDENCE. THE INITIAL POSITION IS ASSESSED WITH 
HIGH CONFIDENCE BASED ON THE WELL-DEFINED EYE IN THE EIR IMAGERY. THE 
INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 
OVERALL CONGRUENCE OF THE OBJECTIVE AND SUBJECTIVE INTENSITY 
ESTIMATES OUTLINED BELOW. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE, 
CHARACTERIZED BY LOW DEEP-LAYER SHEAR, HIGH SEA SURFACE TEMPERATURES 
(SSTS), AND ROBUST RADIAL OUTFLOW, THOUGH TEMPERED BY THE MODERATE 
MID-LEVEL SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.0 - 115 KTS
   CIMSS ADT: 117 KTS AT 281130Z
   CIMSS AIDT: 129 KTS AT 281130Z
   CIMSS D-MINT: 138 KTS AT 281035Z
   CIMSS D-PRINT: 136 KTS AT 281130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: MODERATE MID-LEVEL EASTERLY 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: STY 30W HAS ACCELERATED FROM 9 KTS TO 13 KTS 
OVER THE PAST SIX HOURS IN RESPONSE TO A STRENGTHENING STR TO THE 
NORTH AND A TIGHTENING GRADIENT ALONG THE NORTHERN PERIPHERY OF THE 
CYCLONE. THE SYSTEM IS FORECAST TO CONTINUE ACCELERATING TO A PEAK 
TRANSLATIONAL SPEED OF 18 KTS THROUGH TAU 36. IN THE CURRENT DEEP-
LAYER SYNOPTIC ANALYSIS, A MESOSCALE SUBTROPICAL RIDGE (STR) IS 
POSITIONED NORTHWEST OF THE MARIANA ISLANDS, LINKING WITH A SECONDARY 
RIDGE CENTERED NEAR TAIWAN; TOGETHER WITH THE PRIMARY STR TO THE 
NORTHEAST OF STY 30W, THESE FEATURES FORM A NEAR-CONTINUOUS RIDGE 
AXIS ALONG THE 20N-25N LATITUDE BAND. OVER THE NEXT 36 HOURS, THE 
RIDGE NEAR TAIWAN IS FORECAST TO RETROGRADE WESTWARD AND WEAKEN, THE 
STR TO THE NORTHEAST WILL AMPLIFY AND MAINTAIN ITS POSITION, AND THE 
MESOSCALE RIDGE NORTHWEST OF GUAM WILL WEAKEN AND ULTIMATELY 
DISSIPATE BY TAU 36 AS IT IS ERODED BY A MID-LATITUDE TROUGH 
APPROACHING FROM THE WEST. BY TAU 48, A BROAD COL WILL DEVELOP IN THE 
VICINITY OF IWO TO IN RESPONSE TO THE PASSAGE OF THE TROUGH. BY TAU 
60, STY 30W WILL APPROACH THE SOUTHERN PERIPHERY OF THIS COL AND 
RAPIDLY DECELERATE WITHIN THE WEAKENING STEERING GRADIENT. BY TAU 72, 
STY 30W WILL ENTER THE CENTER OF THE COL AND BECOME QUASI-STATIONARY 
THROUGH TAU 96. BY TAU 96, THE MID-LATITUDE TROUGH WILL LIFT 
NORTHEASTWARD, ALLOWING SUBTROPICAL RIDGING TO BUILD EASTWARD FROM 
MAINLAND CHINA AND DEFLECT STY 30W WEST-SOUTHWESTWARD THROUGH TAU 
120. REGARDING INTENSITY, WHILE STY 30W RETAINS PRIMARILY ANNULAR 
CHARACTERISTICS, IT IS EXPERIENCING MODERATE STRUCTURAL DEGRADATION 
DUE TO MID-LEVEL EASTERLY SHEAR PENETRATING TOWARD THE VORTEX CORE. 
MODEL-DERIVED SOUNDINGS INDICATE THAT THIS MID-LEVEL SHEAR WILL 
GRADUALLY INTENSIFY OVER THE NEXT 24 HOURS AND IMPINGE UPON THE INNER 
CORE, INDUCING MODEST WEAKENING THROUGH TAU 24. SUBSEQUENTLY, MODEL-
DERIVED SOUNDINGS DEPICT A SHARP REDUCTION IN MID-LEVEL SHEAR AFTER 
TAU 24, WHICH WILL ALLOW THE VORTEX TO RE-SYMMETRIZE AND MAINTAIN 
INTENSITY FROM TAU 36 TO TAU 60, LIKELY REGAINING ITS ROBUST ANNULAR 
MORPHOLOGY. FROM TAU 72 TO TAU 96, VERTICAL WIND SHEAR IS FORECAST TO 
INCREASE ONCE MORE, AND THE QUASI-STATIONARY SYSTEM WILL INDUCE 
OCEANIC MIXING AND UPWELLING OF COOLER SUBSURFACE WATERS. HOWEVER, 
THESE THERMODYNAMIC AND DYNAMIC INHIBITORS WILL BE PARTIALLY 
MITIGATED BY ENHANCED POLEWARD OUTFLOW ALOFT. THE NET EFFECT WILL BE 
A GRADUAL WEAKENING TREND THROUGH TAU 96, FOLLOWED BY INTENSITY 
STABILIZATION THROUGH TAU 120 AS THE SYSTEM ACCELERATES WEST-
SOUTHWESTWARD AND EXITS THE UPWELLED COOL WAKE. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN 
GOOD OVERALL AGREEMENT THROUGH THE ENTIRE FORECAST PERIOD. CROSS-
TRACK SPREAD IS MINIMAL THROUGH TAU 48, INCREASING TO 100 NM AT TAU 
72. ENSEMBLE SUITES ALSO EXHIBIT STRONG AGREEMENT THROUGH TAU 72 WITH 
MINIMAL MEMBER DISPERSION. AFTER TAU 72, INTRA-ENSEMBLE DISPERSION 
INCREASES, THOUGH THE ENSEMBLE MEANS REMAIN IN STRONG AGREEMENT 
REGARDING THE POLEWARD TURN, THE SUBSEQUENT QUASI-STATIONARY PHASE, 
AND THE LATE-PERIOD DEFLECTION TO THE WEST-SOUTHWEST. THE 
DETERMINISTIC JTWC CONSENSUS PACKAGE DEPICTS A CONSISTENT SYNOPTIC 
SCENARIO. CROSS-TRACK SPREAD INCREASES TO 210 NM BY TAU 120, WHILE 
SIGNIFICANT ALONG-TRACK SPREAD EMERGES AFTER TAU 96, PARTICULARLY 
BETWEEN THE PROGRESSIVE GALWEM AND THE SLOWER GEFS MEAN, REACHING 275 
NM BY TAU 120. THROUGH TAU 72, NAVGEM BOUNDS THE SOUTHERN EDGE OF THE 
GUIDANCE ENVELOPE, WHILE THE ECEPS MEAN BOUNDS THE NORTHERN EDGE. 
AFTER TAU 72, GALWEM BECOMES THE SOUTHERN OUTLIER, WHILE THE GEFS 
MEAN AND EXPERIMENTAL GOOGLE DEEPMIND (GDM) DEFINE THE NORTHERN 
BOUNDARY. THE REMAINDER OF THE AI MODELS CLUSTER WITHIN THE NORTHERN 
HALF OF THE ENVELOPE, WHEREAS THE DETERMINISTIC ECMWF RESIDES IN THE 
SOUTHERN HALF. THE OFFICIAL JTWC FORECAST TRACK IS PLACED NEAR THE 
MULTI-MODEL CONSENSUS MEAN (CONW) THROUGH THE FORECAST PERIOD. 
INTENSITY GUIDANCE IS IN GOOD AGREEMENT, AND THE JTWC INTENSITY 
FORECAST CLOSELY TRACKS THE CTCX CONSENSUS THROUGH TAU 72 BEFORE 
BLENDING TOWARD THE HWRF SOLUTION THROUGH THE REMAINDER OF THE 
FORECAST PERIOD. 

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