Advisories

WDPN31 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.4N 128.2E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 307 NM SOUTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) AND PROXY VISIBLE (PROXYVIS)
SATELLITE IMAGERY INDICATES THAT TROPICAL STORM (TS) 25W IS 
UNDERGOING STEADY CONVECTIVE CONSOLIDATION AND MATURATION. DEEP 
CONVECTION CONTINUES TO PULSE, BUT HAS DEMONSTRATED PERSISTENCE 
DESPITE MODERATE SOUTHERLY VERTICAL WIND SHEAR (VWS) OVER THE PAST 
SIX HOURS, CHARACTERIZED BY PERSISTENT OVERSHOOTING TOPS CONCENTRATED 
NEAR THE INNER CORE. ANIMATED WATER VAPOR IMAGERY AS WELL AS CIMSS 
AND CIRA ATMOSPHERIC MOTION VECTORS (AMVS) INDICATE A SPLIT IN THE 
OUTFLOW-LEVEL ENVIRONMENTAL FLOW AROUND THE CORE AND ASSOCIATED 
VORTEX. THIS CONFIGURATION SUGGESTS SIGNIFICANTLY REDUCED LOCAL 
VERTICAL SHEAR DIRECTLY OVER THE VORTEX CORE, ALTHOUGH SATELLITE 
OBSERVATIONS ARE RESTRICTED TO OUTFLOW LEVELS AND NUMERICAL SOUNDINGS 
CONTINUE TO DEPICT MODERATE, ALBEIT RELAXING, MID-LEVEL SHEAR. A 
250853Z WSF-M 37GHZ IMAGE PROVIDED INITIAL CONFIRMATION OF A COMPACT 
LOW-LEVEL CIRCULATION CENTER (LLCC) EMBEDDED BENEATH DEEP CONVECTION, 
AND APPROACHING VERTICAL ALIGNMENT. A 251224Z ASCAT-C PASS REVEALED A 
SMALL BUT WELL-ORGANIZED LLCC WITH STRENGTHENING WINDS AND AN 
EXPANDING WIND FIELD; HOWEVER, A SLIGHT TILT PERSISTS, WITH 
CONVECTIVE BURSTING CONFINED PRIMARILY TO THE UPSHEAR-LEFT QUADRANT 
RELATIVE TO THE SURFACE CIRCULATION. THE INITIAL POSITION IS ASSESSED 
WITH HIGH CONFIDENCE BASED ON THE ASCAT-C DATA. THE INITIAL INTENSITY 
IS ASSESSED WITH HIGH CONFIDENCE BASED ON A BLEND OF SUBJECTIVE AND 
OBJECTIVE INTENSITY ESTIMATES NOTED BELOW, SUPPORTED BY THE ASCAT 
PASS. ENVIRONMENTAL CONDITIONS ARE FAVORABLE, WITH DECREASING SHEAR, 
HIGH SSTS (29-30C), ELEVATED OCEAN HEAT CONTENT (OHC), AND MODERATE 
TO STRONG POLEWARD OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF AN EXPANSIVE
DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS ADT: 51 KTS AT 251150Z
   CIMSS AIDT: 44 KTS AT 251150Z
   CIMSS D-PRINT: 52 KTS AT 251240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: MODERATE, BUT DECREASING, MID-LEVEL SOUTHEASTERLY
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: TS 25W HAS TRACKED NORTHWESTWARD AT A STEADY
12-13 KNOTS OVER THE PAST SIX HOURS ALONG THE SOUTHWESTERN FLANK
OF THE LARGE STR TO THE SOUTH OF JAPAN. OVER THE NEXT 12 HOURS, 25W
WILL BEGIN TO DECELERATE AND TURN GRADUALLY NORTHWARD AS IT ENTERS
A COL REGION/WEAKNESS IN THE RIDGE. FROM TAU 12 TO TAU 36, 25W WILL
GRADUALLY CROSS THE RIDGE AXIS, MAINTAINING A REDUCED TRANSLATION
SPEED OF 5-6 KNOTS AS IT PASSES EAST OF MIYAKOJIMA AND THE SOUTHERN
RYUKYUS. BY TAU 48, 25W WILL REACH ITS CLOSEST POINT OF APPROACH 
(CPA) TO OKINAWA AND BEGIN TO ACCELERATE AS THE STR DRIFTS 
SOUTHWESTWARD AND ELONGATES ALONG A SOUTHWEST-NORTHEAST AXIS. A 
PASSING MID-LATITUDE TROUGH TO THE NORTH SHOULD EXERT SUFFICIENT 
FORCING AND EXTEND FAR ENOUGH EQUATORWARD TO CAPTURE 25W AS IT TRACKS
PAST THE NORTHERN RYUKYUS, PROMOTING FURTHER ACCELERATION FROM TAU 72
THROUGH THE END OF THE FORECAST. BY TAU 120, 25W WILL BE POSITIONED
SOUTH OF TOKYO AND COMMENCE EXTRATROPICAL TRANSITION (ETT). REGARDING 
INTENSITY: GIVEN IMMINENT VERTICAL AXISYMMETRIZATION AND AN 
INCREASINGLY FAVORABLE ENVIRONMENT, 25W IS PROJECTED TO MAINTAIN A 
STEADY INTENSIFICATION RATE WITHIN THE NEXT 12 HOURS. THE FORECAST 
STOPS JUST SHY OF EXPLICITLY PREDICTING RAPID INTENSIFICATION (RI); 
HOWEVER, DUE TO ITS COMPACT CORE, 25W MAY OUTPACE CONSENSUS GUIDANCE 
AND ATTAIN A HIGHER RATE OF INTENSIFICATION THROUGH TAU 48. AFTER 
PASSING OKINAWA, 25W WILL ENCOUNTER INCREASING ENVIRONMENTAL SHEAR, 
INITIATING A GRADUAL WEAKENING TREND. THE RATE OF WEAKENING WILL 
ACCELERATE AFTER TAU 72 AS NORTHWESTERLY SHEAR INCREASES SHARPLY, 
SSTS COOL, AND 25W BEGINS ETT. TRACK GUIDANCE REMAINS POLARIZED INTO 
TWO DISTINCT REGIMES. THE ALTERNATIVE SCENARIO REFLECTED IN SELECT 
DYNAMICAL GUIDANCE (GALWEM, NAVGEM, GFS, HAFS-A, AND CTCX) CONTINUES 
TO DEPICT RECURVATURE ARRESTED BY A QUASI-STATIONARY MEANDER NEAR 
OKINAWA WITHIN THE STR COL REGION. GEFS AND MOGREPS PARTIALLY EXHIBIT 
THIS TENDENCY, WHEREAS THE FULL SUITE OF AI GUIDANCE ALONGSIDE 
DETERMINISTIC ECMWF CONSISTENTLY DEPICTS A PROGRESSIVE RECURVATURE 
SCENARIO, WHICH THE JTWC FORECAST CONTINUES TO FAVOR. 

MODEL DISCUSSION: THE OVERALL ORIENTATION OF TRACK GUIDANCE HAS NOT 
CHANGED SIGNIFICANTLY, WITH A CONTINUED BIFURCATION AMONG THE MODEL 
SUITES. THIS REPRESENTS A STRUCTURAL DICHOTOMY BETWEEN THE MAJORITY 
OF PHYSICS-BASED DYNAMICAL MODELS (EXCLUDING ECMWF) VERSUS THE AI 
SUITES AUGMENTED BY ECMWF AND ECEPS. WHILE CONSENSUS BETWEEN ECMWF 
AND AI GUIDANCE BOLSTERS CONFIDENCE IN THE PRIMARY RECURVING 
SOLUTION, PERSISTENCE IN THE ALTERNATIVE QUASI-STATIONARY SCENARIO 
WARRANTS MEASURED FORECAST CONFIDENCE, OWING LARGELY TO THE MARGINAL 
AMPLITUDE AND DYNAMICAL FORCING ASSOCIATED WITH THE APPROACHING MID-
LATITUDE SHORTWAVE. IN SUMMARY, NAVGEM STALLS 25W SOUTHWEST OF 
OKINAWA, WHILE THE HIGH-SPEED OUTLIER WINDBORNE AI TRANSLATES THE 
SYSTEM NORTHEASTWARD AT OVER 30 KNOTS, PRODUCING AN ALONG-TRACK 
SPREAD EXCEEDING 1000 NM BY TAU 120. GFS AND ITS CORRESPONDING 
CLUSTER GENERALLY STALL THE SYSTEM EAST OF OKINAWA. THE REMAINING AI 
MODELS CLUSTER NEAR THE JTWC FORECAST POSITION AT TAU 120, WHILE 
ECMWF AND ECEPS LAG APPROXIMATELY 150 NM BEHIND. ENSEMBLES EXHIBIT 
EXTREME ALONG-TRACK DISPERSION, WITH ENVELOPE EXTENTS RANGING FROM 
TAIWAN TO HOKKAIDO. THE JTWC FORECAST HEAVILY FAVORS THE AI CONSENSUS 
MEAN THROUGH THE FORECAST PERIOD, WITH MEDIUM CONFIDENCE THROUGH TAU 
72 AND LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE REMAINS 
DIVERGENT: CTCX AND COTC INDICATE LITTLE TO NO INTENSIFICATION, 
WHEREAS HAFS-A AND THE RI AIDS (RIDE, RIPA, RI35) PROJECT A PEAK 
INTENSITY BETWEEN 100-115 KNOTS. THE REMAINDER OF THE GUIDANCE, 
INCLUDING GOOGLE DEEPMIND, CAPS INTENSITY NEAR 85 KNOTS. THE JTWC 
FORECAST ALIGNS CLOSELY WITH THE DEEPMIND TRACKER, THOUGH A HIGHER 
PEAK (NEARING HAFS-A SOLUTIONS) REMAINS DYNAMICALLY PLAUSIBLE SHOULD 
INNER-CORE VORTEX ALIGNMENT COMPLETE RAPIDLY. 

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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