Advisories

WDPN31 PGTW 250900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.7N 129.3E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 358 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN ASYMMETRIC 
LOW-LEVEL CIRCULATION CENTER (LLCC), WITH VIGOROUS CONVECTION
DEVELOPING NEAR THE CENTER OF A ROUGHLY CIRCULAR CENTRAL DENSE 
OVERCAST (CDO) FEATURE. A RECENT 250444Z ATMS 89GHZ MICROWAVE PASS
RESOLVED STRUCTURAL DETAILS OF THE VORTEX BENEATH THE CDO CANOPY.
THERE APPEARS TO BE A RELATIVELY STRONG MID-LEVEL VORTEX ASSOCIATED
WITH THE DEEP CONVECTION AND OVERSHOOTING TOPS, WHILE THE SURFACE
LLCC REMAINS TILTED TO THE SOUTHEAST, ALTHOUGH VERTICAL DECOUPLING
HAS DIMINISHED COMPARED TO 24 HOURS AGO. GFS AND ECMWF MODEL-DERIVED
SOUNDINGS AND ENVIRONMENTAL PROFILES SUGGEST RELATIVELY LIGHT DEEP-
LAYER SHEAR, WITH MODERATE MID-LEVEL SHEAR TEMPORARILY RETARDING 
VERTICAL ALIGNMENT. ANIMATED WATER VAPOR IMAGERY DEPICTS A BOW-SHAPED 
BAND OF UPPER-LEVEL OUTFLOW EXPANDING EASTWARD FROM THE CENTER OF 
25W, SUGGESTING THAT AT THE MID- AND UPPER-LEVELS, SHEAR IS RELAXING 
IN THE VICINITY OF THE CORE AND ENVIRONMENTAL VENTILATION IS 
DIMINISHING, FAVORING PROGRESSIVE SYSTEM ORGANIZATION. THE INITIAL 
POSITION IS ASSESSED WITH LOW CONFIDENCE DUE TO THE LACK OF RECENT 
HIGH-RESOLUTION MICROWAVE IMAGERY AND THE OBSCURED LLCC. THE INITIAL 
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE 
OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES NOTED BELOW. 
ENVIRONMENTAL CONDITIONS ARE FAVORABLE, WITH THE PRIMARY INHIBITING 
FACTOR BEING THE TILTED NATURE OF THE VORTEX.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS SATCON: 44 KTS AT 250640Z
   CIMSS ADT: 47 KTS AT 250540Z
   CIMSS AIDT: 41 KTS AT 250540Z
   CIMSS D-MINT: 40 KTS AT 250444Z
   CIMSS D-PRINT: 45 KTS AT 250540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: HIGH MID-LEVEL SOUTHERLY SHEAR; DRY AIR WRAPPING
INTO THE CORE ALONG THE SOUTHEASTERLY FLANK. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 25W CONTINUES TRACKING NORTHWESTWARD
ALONG THE SOUTHWESTERN FLANK OF THE LARGE STR POSITIONED TO THE
NORTHEAST. TRANSLATION SPEED WILL DECREASE OVER THE NEXT 12 HOURS
AS THE SYSTEM APPROACHES THE AXIS OF THE RIDGE AND THE ASSOCIATED
COL REGION BETWEEN THE STR TO THE EAST AND A SECONDARY STR OVER
CENTRAL CHINA. BETWEEN TAUS 24 AND 48, THE SYSTEM WILL SLOWLY ROUND
THE RIDGE AXIS AND GRADUALLY TURN NORTHEASTWARD TO THE EAST OF THE
SOUTHERN RYUKYU ISLANDS. BEYOND TAU 48, THE STR TO THE EAST PROGRESSES
RAPIDLY NORTHEASTWARD WHILE ELONGATING ALONG A SOUTHWEST-TO-NORTHEAST
AXIS. SIMULTANEOUSLY, A MID-LATITUDE SHORTWAVE TROUGH PASSES OVER 
JAPAN, AND THIS SYNOPTIC EVOLUTION WILL ALLOW TS 25W TO ACCELERATE 
NORTHEASTWARD, ROUGHLY PARALLELING THE NORTHERN RYUKYUS AND THE 
JAPANESE MAIN ISLANDS FROM TAU 48 ONWARDS. REGARDING INTENSITY, 25W 
REMAINS TEMPORARILY CONSTRAINED BY MODERATE TO STRONG MID-LEVEL SHEAR 
AND DRY MID-LEVEL AIR ENTRAINMENT. MODEL FIELDS, HOWEVER, SUGGEST 
THAT DRY AIR WILL DILUTE/MIX OUT AND SHEAR WILL CONTINUE TO DECREASE 
OVER THE NEXT 12 TO 18 HOURS, ALLOWING THE VORTEX TO VERTICALLY ALIGN 
AND BECOME SYMMETRIC. ONCE THIS OCCURS, 25W WILL INTENSIFY RAPIDLY AS 
IT ROUNDS THE RIDGE AXIS. PEAK INTENSITY IS EXPECTED AROUND TAU 36 
AND WILL PERSIST THROUGH TAU 60, AS COMPETING DYNAMICAL FORCING 
(INCREASING SHEAR COUNTERBALANCED BY ROBUST POLEWARD OUTFLOW) GOVERNS 
THE CORE REGION. NORTHWESTERLY SHEAR WILL RAPIDLY INCREASE AFTER TAU 
72, USHERING IN SIGNIFICANT DRY AIR AND CONVERGENT FLOW ALOFT, 
RESULTING IN RAPID WEAKENING THROUGH THE REMAINDER OF THE FORECAST 
PERIOD. THERE REMAINS CONSIDERABLE UNCERTAINTY IN THE FORECAST, 
THOUGH AVAILABLE MODEL GUIDANCE IS STARTING TO CONVERGE TOWARD 
GREATER CONSENSUS. GUIDANCE REMAINS BIFURCATED INTO TWO SCENARIOS; 
THE SECONDARY SCENARIO IS CONFINED TO SELECT DYNAMICAL GUIDANCE (GFS, 
UKMET, HAFS-A, COAMPS-TC, AND NAVGEM), WHICH DEPICTS 25W BECOMING 
QUASI-STATIONARY IN THE VICINITY OF OKINAWA AROUND TAU 72-96 PRIOR TO 
TURNING EQUATORWARD. THE FACT THAT THE ECMWF, ECMWF ENSEMBLE (ECEPS), 
AND GFS ENSEMBLE (GEFS) HAVE SHIFTED TO THE PRIMARY RECURVATURE 
SCENARIO LENDS INCREASED CONFIDENCE IN THAT SOLUTION, THOUGH THE 
QUASI-STATIONARY OUTCOME CANNOT BE EXCLUDED. INTENSITY IS TIGHTLY 
COUPLED TO TRACK; A STALLED SYSTEM WOULD REMAIN OVER FAVORABLE SSTS 
AND LOW SHEAR LONGER, REACHING A HIGHER PEAK INTENSITY APPROXIMATELY 
24 HOURS LATER THAN CURRENTLY FORECAST.

MODEL DISCUSSION: TRACK GUIDANCE IS STEADILY CONVERGING WITH EACH
SUCCESSIVE CYCLE. THE ECMWF, ECEPS, GEFS, AND GALWEM NOW ALIGN WITH
ARTIFICIAL INTELLIGENCE/MACHINE LEARNING (AI/ML) CONSENSUS IN 
DEPICTING A RECURVING TRACK. FURTHERMORE, THE DETERMINISTIC ECMWF 
OUTPACES BOTH THE AI CONSENSUS AND EC-AIFS TRACKERS FROM TAU 96 
ONWARDS. WHILE GFS REMAINS IN THE SLOW/STALLED CLUSTER, IT HAS 
TRENDED PROGRESSIVELY FARTHER NORTHEASTWARD BEFORE STALLING WITH EACH 
RECENT CYCLE. THESE SHIFTS PROVIDE INCREASED CONFIDENCE IN THE JTWC 
FORECAST TRACK. HOWEVER, ALONG-TRACK SPREAD REMAINS SIGNIFICANT, 
REACHING 900 NM BETWEEN THE NAVGEM SOUTHWEST OF OKINAWA AND THE 
DEEPMIND AND WINDBORNE AI SOLUTIONS SOUTHEAST OF TOKYO BY TAU 120. 
THE AI CONSENSUS STRONGLY COINCIDES WITH EC-AIFS AND DETERMINISTIC 
ECMWF GUIDANCE, AND THE JTWC FORECAST HEAVILY FAVORS THIS CLUSTER 
THROUGH THE PERIOD. CONFIDENCE IS MEDIUM THROUGH TAU 72 AND LOW 
THEREAFTER; PERSISTENCE OF THESE TRENDS MAY WARRANT UPGRADING LONG-
RANGE CONFIDENCE TO MEDIUM IN SUBSEQUENT BULLETINS. INTENSITY 
GUIDANCE HAS ALSO NARROWED SPREAD OVER THE PAST 24 HOURS, WITH PEAK 
PROJECTIONS CONFINED LARGELY TO 80-105 KNOTS. HAFS-A AND CTCX REMAIN 
THE MOST AGGRESSIVE SOLUTIONS AND DELAY THE PEAK BY APPROXIMATELY 24 
HOURS. THE JTWC INTENSITY FORECAST ALIGNS CLOSELY WITH GOOGLE 
DEEPMIND GUIDANCE THROUGH TAU 60, REMAINING 10-15 KNOTS HIGHER 
THEREAFTER. CONFIDENCE IS MEDIUM THROUGH TAU 72 AND LOW THEREAFTER.   

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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