Advisories

WDPN31 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.9N 133.1E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 542 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN
ASYMMETRIC SYSTEM EXHIBITING AN IRREGULAR CENTRAL DENSE OVERCAST
(CDO) STRUCTURE WITH ENHANCED CONVECTIVE BURSTS CONFINED TO THE 
NORTHERN PERIPHERY OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 
240436Z AMSR3 COLOR-ENHANCED 89GHZ MICROWAVE IMAGE REVEALED A 
PRONOUNCED ASYMMETRY IN THE LOW-LEVEL STRUCTURE AND SIGNIFICANT 
VERTICAL TILT OF THE VORTEX CORE, INDICATIVE OF MODERATE MID-LEVEL 
SOUTHERLY VERTICAL WIND SHEAR (VWS). SYNTHETIC MICROWAVE IMAGERY
SUGGESTS THE VORTEX TILT HAS INTENSIFIED, WITH THE MID-LEVEL 
CIRCULATION DISPLACED APPROXIMATELY 30 NM NORTHWEST OF THE 
INCREASINGLY DISRUPTED AND PARTIALLY EXPOSED LLCC. EARLIER 
SCATTEROMETRY DATA DEPICTED A VERY ASYMMETRIC WIND FIELD, WITH GALE-
FORCE WINDS RESTRICTED TO THE NORTHERN SEMICIRCLE, WHILE WINDS TO THE 
SOUTH WERE GENERALLY LESS THAN 20-25 KNOTS. ANIMATED WATER VAPOR 
IMAGERY AND CIRA ADVECTED LAYER TOTAL PRECIPITABLE WATER (TPW) 
INDICATE A SUBSTANTIAL MID-LEVEL DRY AIR INTRUSION PERSISTING ACROSS 
THE SOUTHERN QUADRANT OF THE CIRCULATION. THE SYSTEM IS STRUGGLING TO
ESTABLISH AXISYMMETRY DUE TO THE DELETERIOUS COMBINATION OF MODERATE 
VWS AND MID-LEVEL DRY AIR ENTRAINMENT INTO THE CORE. THE INITIAL 
POSITION IS ASSESSED WITH MODERATE CONFIDENCE BASED ON AN 
EXTRAPOLATION OF THE AMSR3 DATA NOTED ABOVE. THE INITIAL INTENSITY IS 
ASSESSED WITH MODERATE CONFIDENCE, BASED ON A BLEND OF THE SUBJECTIVE 
AND OBJECTIVE INTENSITY ESTIMATES NOTED BELOW. ENVIRONMENTAL 
CONDITIONS ARE GENERALLY FAVORABLE, WITH THE NOTABLE EXCEPTIONS 
DISCUSSED ABOVE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED SOUTH OF HONSHU. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   CIMSS SATCON: 44 KTS AT 240416Z
   CIMSS ADT: 47 KTS AT 240540Z
   CIMSS AIDT: 39 KTS AT 240540Z
   CIMSS D-MINT: 49 KTS AT 240418Z
   CIMSS D-PRINT: 50 KTS AT 240640Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: VORTEX TILT; MODERATE MID-LEVEL SHEAR; DRY AIR
ENTRAINMENT ALONG THE SOUTHERN FLANK. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 25W IS FORECAST TO
CONTINUE TRACKING NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF
THE STR FOR THE NEXT 36 HOURS. FORWARD TRANSLATIONAL SPEED IS 
PROJECTED TO DECELERATE SIGNIFICANTLY AFTER TAU 24 AS THE STR 
WEAKENS AND SHIFTS SLIGHTLY EASTWARD. THE SYSTEM IS EXPECTED TO 
APPROACH THE STR AXIS BY TAU 48, DECELERATING FURTHER TO 5-6 KNOTS AS 
IT MOVE INTO A DEEP-LAYER COL REGION LOCATED BETWEEN THE PRIMARY STR 
TO THE EAST AND A SECONDARY STR OVER CENTRAL CHINA. THE TAU 48 TO TAU 
60 TIMEFRAME REPRESENTS THE CRITICAL FORECAST DECISION POINT, AS TS 
25W BECOMES WEAKLY STEERED WITHIN THIS COL REGION AT THE RIDGE AXIS. 
THE BASELINE FORECAST IS PREDICATED ON A MID-LATITUDE SHORTWAVE 
TROUGH TRANSITING TO THE NORTH PROVIDING SUFFICIENT FORCING TO 
EXTRACT TS 25W FROM THE COL REGION, FACILITATING A RECURVATURE ROUTE 
AROUND THE SUBTROPICAL RIDGE AXIS TOWARD THE NORTHEAST. THIS SCENARIO 
IS SUPPORTED BY ALL OF THE ARTIFICIAL INTELLIGENCE (AI) MODELS AND TO 
A LESSER EXTENT BY THE ECMWF AND THE GEFS ENSEMBLE MEAN. HOWEVER, 
SUBSTANTIAL UNCERTAINTY PERSISTS REGARDING THE TRACK SCENARIO. THE 
TRANSITING MID-LATITUDE TROUGH EXHIBITS MODEST AMPLITUDE AND LIMITED 
THERMODYNAMIC SUPPORT, RENDERING AN ALTERNATE TRACK REALIZATION 
PLAUSIBLE. THE ALTERNATE SCENARIO IS BEST EXEMPLIFIED BY THE GFS, 
WHICH IS CONSISTENT WITH THE OTHER MODELS THROUGH TAU 48. AFTER TAU 
60 HOWEVER THE GFS DEPICTS A RAPID SLOWDOWN IN TRACK SPEED, WITH THE 
SYSTEM BECOMING NEARLY STATIONARY AFTER TAU 72, TO THE SOUTH OF 
OKINAWA. THE GFS SHOWS THE SYSTEM REMAINING STUCK IN THE COL-REGION, 
AS THE TROUGH TO THE NORTH IS TOO WEAK TO PULL IT POLEWARD. THE GFS 
SHOWS TS 25W REMAINING SOUTH OF OKINAWA THROUGH TAU 120 BEFORE 
EVENTUALLY TURNING SOUTHWARD BEYOND DAY SIX. IN REGARDS TO INTENSITY, 
TS 25W WILL STRUGGLE TO INTENSIFY OVER THE NEXT 12 TO 24 HOURS UNDER 
THE NEGATIVE INFLUENCE OF MODERATE MID-LEVEL SHEAR AND DRY AIR 
ENTRAINMENT. BY TAU 24, NUMERICAL GUIDANCE INDICATES AN IMPROVING 
THERMODYNAMIC ENVIRONMENT CHARACTERIZED BY ENHANCED UPPER-LEVEL 
DIVERGENT OUTFLOW, DECREASING VWS, AND REGIONAL MOISTENING, ENABLING 
CONDITIONS CONDUCIVE TO A PERIOD OF RAPID INTENSIFICATION (RI) 
BETWEEN TAU 24 AND TAU 48. THE SYSTEM IS PROJECTED TO REACH ITS PEAK 
INTENSITY NEAR THE RIDGE AXIS BEFORE COMMENCING A STEADY WEAKENING 
TREND DRIVEN BY INCREASING SHEAR AND DRY AIR ENTRAINMENT. IN THE 
ALTERNATE SCENARIO, HOWEVER, THE EXTENDED DWELL TIME IN A FAVORABLE 
ENVIRONMENT WOULD DELAY THE ONSET OF SHEAR DEGRADATION, POTENTIALLY 
ALLOWING TS 25W TO ATTAIN A HIGHER PEAK INTENSITY ROUGHLY 24 HOURS 
LATER THAN PREDICTED IN THE BASELINE OUTLOOK.

MODEL DISCUSSION: MODEL GUIDANCE IS HIGHLY UNCERTAIN, WITH A LARGE
AMOUNT OF PRIMARILY ALONG-TRACK SPEED, WITH THE UNCERTAINTY
FOCUSED BETWEEN THE AI-BASED AND THE PHYSICS-BASED MODELS, AND
AFTER TAU 60. UP TO TAU 60, THE MODELS ARE TIGHTLY CONFINED TO A
NARROW ENVELOPE, SUPPORTING THE JTWC FORECAST WITH HIGH CONFIDENCE.
THE ONLY OUTLIERS DURING THIS TIME ARE THE ECMWF WHICH BEGINS TO
PULL THE SYSTEM NORTHWARD AFTER TAU 48 AND LIES SOUTH AND EAST OF
ALL THE OTHER MODELS BY TAU 60, AND THE NAVGEM-UKMET COMBO WHICH
TRACKS THE SYSTEM STRAIGHT NORTHWESTWARD, OPENING UP SOME DISTANCE
TO THE SOUTH AND WEST OF THE ENVELOPE. AT THIS POINT, THINGS
DIVERGE RAPIDLY AND SIGNIFICANTLY. THE AI-BASED MODELS START TO
OUTRACE THE OTHERS AS EARLY AS TAU 72, INCREASING THE RATE OF
ACCELERATION THEREAFTER, RESULTING IN THE MOST AGGRESSIVE OF THEM
(EXPERIMENTAL GOOGLE DEEP MIND) BEING POSITIONED OVER 500NM
NORTHEAST OF THE CONSENSUS MEAN BY TAU 120. WHILE THE CONSENSUS
MEAN IS BEING DRAGGED SLOWER BY THE UNREALISTIC NAVGEM-UKMET COMBO
PULLING THE SYSTEM TOWARDS TAIPEI, ALL OF THE PHYSICS-BASED MODEL
GUIDANCE SHOWS A MUCH SLOWER PROGRESSION NORTHWARD, WITH THE GFS
NEVER RECURVING THE SYSTEM. THE EXPERIMENTAL JTWC SUPER-ENSEMBLE
MEAN DEPICTS A SLOW RECURVE SCENARIO, WITH ACCELERATION OCCURRING
PRIMARILY BEYOND TAU 120. THE JTWC FORECAST IS PLACED NEAR THE AI
CONSENSUS THROUGH TAU 60. THEREAFTER IT IS POSITIONED NEAR THE
MID-POINT BETWEEN THE AI AND TRADITIONAL CONSENSUS MEAN POSITIONS,
ROUGHLY CONSISTENT WITH THE SUPER-ENSEMBLE MEAN. INTENSITY GUIDANCE
IS ALSO MIXED, AND HIGHLY DEPENDENT UPON THE TRACK FORECAST,
THEREFORE HIGHLY UNCERTAIN. THE HAFS-A IS VERY AGGRESSIVE, REACHING
A PEAK APPROACHING 130 KNOTS BY TAU 72, THOUGH TRACK-WISE, IT IS
CONSISTENT WITH THE GFS. THE CTCX AND SHIPS GUIDANCE MEANWHILE IS
MUCH LESS AGGRESSIVE, REACHING A MAXIMUM OF JUST 75 KNOTS.
MEANWHILE, MULTIPLE RI AIDS HAVE TRIGGERED, SOME REACHING AS HIGH AS
140 KNOTS (COAMPS-TC ENSEMBLE), WHILE MULTIPLE ENSEMBLE-BASED RI
PROBABILITY ESTIMATES EXCEED 80 PERCENT BETWEEN TAU 24 AND 48. THE
JTWC FORECAST SPECIFICALLY CALLS FOR RI DURING THE 24-48 HOUR
POINT, AND MOST CLOSELY TRACKS THE OPERATIONAL GOOGLE DEEPMIND
INTENSITY GUIDANCE. HOWEVER, CONFIDENCE IN BOTH THE TRACK AND
INTENSITY IS LOW AFTER TAU 72 DUE TO HIGHLY UNCERTAIN NATURE OF THE
FORECAST AND POTENTIAL ALTERNATE SCENARIO.   

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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