Advisories

WDPS31 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01P (WATI) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.2S 163.2W
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 442 NM EAST OF PAGO PAGO
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT INNER CORE OF DEEP CONVECTION WITH SLIGHTLY ASYMMETRIC SPIRAL
BANDING FEATURES WRAPPING CONCENTRICALLY INTO AN OBSCURED LOW-LEVEL
CIRCULATION CENTER (LLCC). A 170441Z WSF-M COLOR-ENHANCED 37GHZ
MICROWAVE PASS REVEALED A WELL-DEFINED MICROWAVE EYE SIGNATURE,
CHARACTERIZED BY A CYAN RING ENCIRCLING THE EYE AND DEEP CONVECTIVE 
CORES ALONG THE WESTERN AND NORTHERN FLANKS OF THE INNER CORE. THE 
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE, DERIVED FROM A 
SHORT-RANGE EXTRAPOLATION OF THE MICROWAVE EYE SIGNATURE. THE INITIAL 
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY HIGHER 
THAN SUBJECTIVE AGENCY DVORAK FIXES (35-55 KTS) IN DEFERENCE TO THE 
CIMSS D-PRINT ESTIMATE (60 KTS), WHICH IS DEEMED MORE REPRESENTATIVE
OF THE CONSOLIDATED CORE. ENVIRONMENTAL CONDITIONS ARE FAVORABLE FOR
CONTINUED DEVELOPMENT, CHARACTERIZED BY WEAK DEEP-LAYER VERTICAL WIND
SHEAR (VWS), WARM SEA SURFACE TEMPERATURES (SSTS), AND ROBUST 
POLEWARD OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   PHFO: T2.5 - 35 KTS
   NFFN: T3.5 - 55 KTS
   CIMSS SATCON: 54 KTS AT 170740Z
   CIMSS ADT: 45 KTS AT 170540Z
   CIMSS AIDT: 42 KTS AT 170540Z
   CIMSS D-MINT: 46 KTS AT 170443Z
   CIMSS D-PRINT: 60 KTS AT 170710Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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: TC 01P (WATI) EXHIBITED ERRATIC, LOOPING MOTION 
EARLIER IN THE DAY TODAY, BUT SINCE 00Z, HAS STEADIED UP ON A 
SOUTHEASTWARD TRAJECTORY BASED ON MULTIPLE MICROWAVE IMAGE PASSES. 
THE SYSTEM IS FORECAST TO ACCELERATE SOUTHEASTWARD ALONG THE 
SOUTHWESTERN FLANK OF THE STR THROUGHOUT THE ENTIRETY OF THE FORECAST 
PERIOD. REGARDING INTENSITY: TC 01P RESIDES WITHIN A CONDUCIVE 
ENVIRONMENT AND IS PROJECTED TO INTENSIFY STEADILY, REACHING A PEAK 
INTENSITY OF 75 KNOTS NEAR TAU 24. SHOULD INNER-CORE CONSOLIDATION 
ACCELERATE RAPIDLY, AN ONSET OF RAPID INTENSIFICATION (RI) REMAINS 
A POSSIBILITY, POTENTIALLY DRIVING PEAK SURFACE WINDS TOWARD 80-85 
KNOTS. BY TAU 24, HOWEVER, DEEP-LAYER VWS IS PROJECTED TO INCREASE 
SHARPLY, INITIATING A WEAKENING TREND THAT WILL PERSIST THROUGH THE 
BALANCE OF THE FORECAST. TC 01P WILL PASS SOUTH OF THE 26C ISOTHERM 
WITHIN 36 HOURS, AND THIS WILL ACCELERATE THE DECAY RATE. BY TAU 60, 
THE CYCLONE WILL BEGIN TO INTERACT WITH A BAROCLINIC ZONE TO THE 
SOUTH, PHASING WITH THE POLAR JET STREAM TO INITIATE FRONTOGENESIS 
AND MARKING THE START OF EXTRATROPICAL TRANSITION (ETT). COMPLETED 
TRANSITION TO A COLD-CORE GALE IS FORECAST NLT TAU 72.

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT ON THE
OVERALL TRACK, WITH ALL CONSENSUS MEMBERS SUPPORTING A SOUTHEASTWARD 
TRACK THROUGH THE FORECAST PERIOD. CROSS-TRACK SPREAD GRADUALLY 
INCREASES TO 300 NM BY TAU 120. GALWEM DEFINES THE WESTERN (INNER) 
PERIPHERY OF THE GUIDANCE ENVELOPE, WHILE THE DETERMINISTIC GFS 
COVERS THE EASTERN BOUNDARY. THE AI MODELS, DETERMINISTIC ECMWF, AND 
NAVGEM ARE TIGHTLY CLUSTERED PROXIMATE TO THE MULTI-MODEL CONSENSUS 
MEAN, FORMING A TIGHT CONVERGENCE OF SOLUTIONS. THE JTWC TRACK 
CLOSELY FAVORS THE ECMWF RUN THROUGH THE FORECAST POSTURE WITH HIGH 
CONFIDENCE. INTENSITY GUIDANCE CONCURS STRONGLY ON THE SHAPE OF THE 
DEVELOPMENT CURVE. THE BULK OF THE CONSENSUS MEMBERS INDICATE 
INTENSIFICATION UP TO A PEAK BETWEEN 65 KTS (COTC AND SHIPS) AND 75 
KTS (HAFS-A AND DEEPMIND), WHILE RI AIDS (RIDE AND FRIA) DEPICT PEAKS 
ATTAINING 85 KNOTS. THE JTWC INTENSITY FORECAST ALIGNS CLOSELY WITH 
HAFS-A SOLUTIONS WITH MEDIUM CONFIDENCE THROUGH THE FORECAST PERIOD.

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