Advisories

WDPS31 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01P (WATI) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.1S 162.4W
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 340 NM NORTH-NORTHWEST OF RAROTONGA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A BALL
OF ROUGHLY SYMMETRICAL CONVECTION WITH ISOLATED OVERSHOOTING TOPS.
AN 180450Z SSMIS 91GHZ MICROWAVE IMAGE REVEALED AN UPPER-LEVEL
MICROWAVE EYE-LIKE FEATURE, SURROUNDED BY CURVED CONVECTION.
HOWEVER, A CLOSE INSPECTION OF THE MICROWAVE IMAGE SUGGESTS THE
SYSTEM IS IN THE EARLY PHASES OF VORTEX DECOUPLING, WITH SPIRAL
BAND ANALYSIS SUGGESTING THE LOW LEVEL CIRCULATION CENTER (LLCC) IS
NOT ALIGNED WITH THE UPPER-LEVEL CENTER. ANALYSIS OF HAFS-A
CROSS-SECTIONS SUPPORTS THIS ANALYSIS. THE INITIAL POSITION IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED SPIRAL
BAND ANALYSIS OF THE LOW-LEVEL BANDING FEATURES EVIDENT IN THE
MICROWAVE IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON A BLEND OF THE SUBJECTIVE AND OBJECTIVE
INTENSITY ESTIMATES OUTLINED BELOW. ENVIRONMENTAL CONDITIONS ARE
MARGINALLY UNFAVORABLE, WITH RAPIDLY INCREASING SHEAR, DECREASING
SSTS AND STRONG 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: T4.0 - 65 KTS
   PHFO: T2.5 - 35 KTS
   NFFN: T3.5 - 55 KTS
   CIMSS SATCON: 62 KTS AT 180720Z
   CIMSS ADT: 74 KTS AT 180540Z
   CIMSS AIDT: 72 KTS AT 180540Z
   CIMSS D-MINT: 48 KTS AT 180326Z
   CIMSS D-PRINT: 58 KTS AT 180720Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: VORTEX DECOUPLING.

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 CYCLONE (TC) 01P WILL TRACK
SOUTHEASTWARD ALONG THE SOUTHWESTERN FLANK OF THE STR FOR THE
DURATION OF THE FORECAST PERIOD. REGARDING INTENSITY, THE SYSTEM
HAS VERY LIKELY BEGUN THE VORTEX DECOUPLING PROCESS UNDER GRADUALLY
INCREASING VWS. HAFS-A CROSS-SECTIONS AND STATISTICAL GUIDANCE
DEPICT A SHARP INCREASE IN VWS COMMENCING IN THE NEXT 12 HOURS,
COINCIDENT WITH THE SYSTEM CROSSING POLEWARD OF THE 26C ISOTHERM.
FULL VORTEX DECOUPLING SHOULD OCCUR BY TAU 36, AS THE SYSTEM RACES
SOUTHEASTWARD. 01P COMMENCES EXTRATROPICAL TRANSITION (ETT) BY TAU
24, AS IT BEGINS TO INTERACT WITH THE STRONG JET STREAM TO THE
SOUTH, AND A 500MB MAJOR SHORTWAVE TROUGH. BETWEEN TAU 36 AND TAU
48, 01P WILL MOVE INTO PHASE WITH THE 500MB TROUGH, MOVE UNDER THE
JET STREAM AND MERGE INTO THE LOW-LEVEL BAROCLINIC ZONE, AND
TRANSITION TO A STRONG GALE-FORCE LOW PRESSURE AREA. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT, WITH ALL
MEMBERS OF THE CONSENSUS SUPPORTING A SOUTHEASTWARD TRACK THROUGH
THE DURATION OF THE FORECAST. CROSS-TRACK SPREAD INCREASES TO 155NM
BY TAU 48, WITH ECMWF MARKING THE WESTERN EDGE OF THE GUIDANCE
ENVELOPE AND THE GEFS AND ECEPS MEAN MARKING THE EASTERN SIDE. THE
JTWC FORECAST IS POSITIONED NEAR THE OPERATIONAL GOOGLE DEEPMIND
TRACKER WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN STRONG
AGREEMENT, WITH ALL MEMBERS OF THE CONSENSUS INDICATING STEADY
WEAKENING THROUGH THE FORECAST PERIOD. 

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