Advisories

WDPN33 PGTW 070300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (KOGUMA) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.3N 164.0E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 282 NM SOUTH-SOUTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TS 27W
CONTINUING TO STRUGGLE AGAINST MODERATE NORTHEASTERLY VERTICAL WIND
SHEAR (VWS). IN THE ANTECEDENT ANALYSIS, UPPER-LEVEL OUTFLOW-LAYER
WINDS RESISTED THE VWS VECTOR CONSISTENTLY. HOWEVER, OVER THE LAST
SIX HOURS, DESPITE CONTINUOUS DEEP CONVECTIVE FLARES, THE UPPER-LEVEL
OUTFLOW CHANNELS HAVE WEAKENED. THE EASTERLY ENVIRONMENTAL FLOW HAS
PARTIALLY RE-ESTABLISHED ITSELF, ERODING THE EASTERN FLANK OF THE
CENTRAL DENSE OVERCAST (CDO) AND RESTRICTING OUTFLOW ALONG THE
SYSTEMS EASTERN SEMICIRCLE. A 062218Z MHS 89GHZ MICROWAVE PASS 
REVEALED A STRONG MID- TO UPPER-LEVEL ROTATION MET BY CURVED BANDS OF 
DEEP CONVECTION, WITH THE LOW-LEVEL CIRCULATION CENTER (LLCC) 
DISPLACED TO THE EAST. A 061915Z WSF-M COLOR-ENHANCED 37GHZ IMAGE 
REVEALED A SIMILAR DECOUPLED CORE STRUCTURE, EXHIBITING WELL-DEFINED 
BUT EXPOSED LOW-LEVEL BANDING FEATURES ALONG THE EASTERN FLANK, A 
PROMINENT PSEUDO-EYE SIGNATURE, AND AN ELONGATED, RAGGED LLCC 
DISPLACED EAST OF THE MID-LEVEL SYSTEM CENTER. FINALLY, A 062221Z 
PARTIAL ASCAT-B PASS REVEALED A COMPACT LLCC POSITIONED NEAR THE 
SWATH EDGE ALONG THE NORTHEASTERN PERIPHERY OF THE CONVECTIVE 
ENVELOPE. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED 
ON THE CONCURRENT SATELLITE SUITE AND SCATTEROMETER CONGRUENCE. THE 
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, ALIGNED WITH 
OBJECTIVE AND SUBJECTIVE SATELLITE ESTIMATES. ENVIRONMENTAL 
CONDITIONS REMAIN GENERALLY FAVORABLE, CHARACTERIZED BY VERY WARM 
SSTS (30-31C), HIGH OCEAN HEAT CONTENT (OHC), AND MODERATE WESTWARD 
OUTFLOW ALOFT; HOWEVER, SYSTEM-SCALE CONSOLIDATION IS INHIBITED BY A 
TILTED AND ASYMMETRIC VORTEX MORPHOLOGY.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: COMPLEX STEERING ENVIRONMENT GOVERNED BY 
A
SUBTROPICAL RIDGE (STR) FAR TO THE NORTH, DYNAMICAL INFLUENCE FROM TY 
15E SITUATED NORTHEAST OF TS 27W, AND A SECONDARY HIGH-PRESSURE 
CENTER TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.0 - 45 KTS
   PHFO: T3.0 - 45 KTS
   CIMSS SATCON: 50 KTS AT 062100Z
   CIMSS ADT: 59 KTS AT 060000Z
   CIMSS AIDT: 50 KTS AT 060020Z
   CIMSS D-MINT: 65 KTS AT 062158Z
   CIMSS D-PRINT: 54 KTS AT 060020Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: VORTEX TILT; MODERATE MID-LEVEL EASTERLY SHEAR. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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) 27W WILL CONTINUE TRACKING
SLOWLY NORTHWESTWARD ALONG THE SOUTHERN FLANK OF A COMPLEX AND
RELATIVELY WEAK STEERING ENVIRONMENT. THE STR IS CENTERED FAR TO THE
NORTH, WITH A MERIDIONAL EXTENSION TRANSITING JUST WEST OF THE 
DATELINE AND ANCHORING TO THE SECONDARY DEEP-LAYER RIDGE SOUTHEAST OF 
27W. TY 15E RESIDES IN THE SADDLE REGION BETWEEN THE STR AND TS 27W, 
WEAKENING THE STEERING GRADIENT AND CAUSING 27W TO TRANSLATE AT A 
REDUCED SPEED OVER THE NEXT 12 TO 24 HOURS. BY TAU 24, TY 15E WILL 
HAVE PROGRESSED SUFFICIENTLY WESTWARD TO PERMIT DOWNSTREAM RIDGE 
BUILDING, AMPLIFYING THE STEERING FLUX AND ACCELERATING TS 27W 
NORTHWESTWARD THROUGH TAU 72. BEYOND TAU 72, THE FORECAST TRACK 
REACHES A MAJOR BIFURCATION POINT. AI-ML MODELS PREDICT A PERSISTENT, 
GRADUALLY DECELERATING NORTHWESTWARD HEADING, WHEREAS THE MAJORITY OF 
DETERMINISTIC PHYSICS-BASED SUITES STEER THE CYCLONE POLEWARD AT A 
FASTER RATE. BOTH THE ECMWF AND GFS DYNAMICALLY PROJECT RECURVATURE 
OF TY 15E OCCURRING AT A SIMILAR TIMELINE AND TRANSLATION SPEED, BUT 
BIFURCATE ON THE SUBSEQUENT RE-ESTABLISHMENT OF THE STR. THE GFS 
RESOLVES A STRONGER RIDGE EXTENDING WESTWARD NORTH OF TS 27W, WHILE 
THE ECMWF DISSIPATES THE STR EXTENSION. THE AI-ML SUITES ALIGN WITH 
THE GFS SCENARIO BUT DEPICT AN EVEN GREATER RESIDENCE TIME FOR THE 
BLOCKING RIDGE. THE JTWC FORECAST HEAVILY LEANS TOWARD THE AI-MODEL 
SOLUTION, MAINTAINING HIGH-CONFIDENCE TRACK CONTINUITY ON A 
NORTHWESTWARD TRAJECTORY. REGARDING INTENSITY: THE SYSTEM EXHIBITS 
SIGNIFICANT VERTICAL TILT AND ASYMMETRY, CONSTRAINING NEAR-TERM 
INTENSIFICATION FOR THE NEXT 12 HOURS. BY TAU 18, VWS IS PROJECTED TO 
RELAX SUFFICIENTLY TO ALLOW CORE SYMMETRIZATION AND VERTICAL 
ALIGNMENT. COINCIDENT WITH VORTEX ALIGNMENT, TS 27W WILL INTERSECT AN 
EXTENSIVE REGION OF ANOMALOUSLY HIGH OCEAN HEAT CONTENT (REACHING 170 
KJ/CM2). ACCORDINGLY, TS 27W IS PROJECTED TO COMMENCE A RAPID 
INTENSIFICATION (RI) CYCLE NEAR TAU 24 AND PERSIST THROUGH TAU 60,
ATTAINING A PEAK INTENSITY OF AT LEAST 120 KNOTS. PEAK INTENSITY WILL
LIKELY ENVELOPE THE TAU 72 TO 96 WINDOW. THEREAFTER, TS 27W WILL 
ACCELERATE ITS DECAY AS IT CROSSES THE COLD WAKE GENERATED BY TY 15E.

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
72. CROSS-TRACK SPREAD WIDENS TO 170 NM BY TAU 72, BOUNDED BY EC-AIFS
ON THE SOUTHERN ENVELOPE LIMIT AND GFS/GEFS ALONG THE NORTHERN 
BOUNDARY, WHICH DRIFT POLEWARD AS EARLY AS TAU 60. POST-TAU 72, 
NUMERICAL SOLUTIONS BIFURCATE INTO TWO SCHEMES. GFS, GEFS, ECMWF, 
ECEPS, NAVGEM, AND JGSM ROTATE THE CYCLONE SHARPLY NORTHWARD, WITH 
THE DETERMINISTIC ECMWF MODEL AS THE FAST POLEWARD OUTLIER AND THE 
GFS AS THE SLOWEST OF THE RECURVATURE CLUSTER. THE ALTERNATIVE REGIME 
CONSISTS OF THE AI-BASED MODELS, GALWEM, AND THE UKMET ENSEMBLE MEAN, 
WHICH DEPICT A PERSISTENT WEST-NORTHWESTWARD STEERING CURRENT 
ENFORCING A STEADY ACCUMULATED SPEED THROUGH TAU 120. THE TOTAL DAY 5 
CROSS-REGIME BIFURCATION REACHES JUST OVER 600 NM BETWEEN EC-AIFS AND 
DETERMINISTIC ECMWF TRACKERS. THE JTWC FORECAST IS POSITIONED ALONG 
THE COGNITIVE MEDIAN JUST NORTH OF THE OPERATIONAL GOOGLE DEEPMIND 
SOLVER, MAINTAINING HIGH SHORT-TERM CONFIDENCE THAT PROGRESSES TO 
MEDIUM LONG-TERM CONFIDENCE. INTENSITY GUIDANCE CONCURS REASONABLY 
WELL; ONLY GFS AND STATISTICAL DECAY-SHIPS FAIL TO CAPTURE 
SIGNIFICANT INTENSIFICATION. THE REMAINING MESOSCALE MODELS (HAFS-A, 
COAMPS-TC, DEEPMIND) AND STATISTICAL-DYNAMICAL RI AIDS (DTOP, RICN, 
RIDE, CTR1, RIPA, FRIA) ALL TRIGGER AN RI INITIATION BY TAU 24. PEAK 
PROJECTED INTENSITY WITHIN THE MODEL SUITE IS 125 KNOTS (HAFS-A), 
CLUSTERING NEAR 120 KNOTS BETWEEN TAUS 72 AND 96, FOLLOWED BY A SHARP 
DOWNSTREAM DECAY SLOPE ON COLD SST WAKES. THE JTWC INTENSITY FORECAST 
LEANS ON THE DEEPMIND CURVE THROUGH TAU 12, BLENDS INTO THE DYNAMIC 
RI AIDS CLUSTER THROUGH TAU 72, AND COINCIDES WITH HAFS-A THROUGH THE 
END OF THE FORECAST WINDOW. 

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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