Advisories

WDPN33 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.3N 156.6E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 648  NM NORTH-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
THE SATELLITE PRESENTATION OF TY 27W HAS IMPROVED MARKEDLY OVER
THE PAST SIX HOURS, INDICATIVE OF AN ONGOING RAPID INTENSIFICATION
TREND. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS
SPIRALING DEEP CONVECTIVE BANDING WRAPPING INTO AN INCREASINGLY
ORGANIZED CIRCULATION SURROUNDING A 7 NM DIAMETER EYE. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON SATELLITE EYE
FIXES FROM PGTW AND RJTD. THE INITIAL INTENSITY OF 75 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE FAVORING THE HIGH END OF
SUBJECTIVE DVORAK AND AUTOMATED INTENSITY ESTIMATES LISTED BELOW, TO 
ACCOUNT FOR THE RAPID RATE OF CHANGE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.5 - 77 KTS
   CIMSS SATCON: 82 KTS AT 081958Z
   CIMSS ADT: 77 KTS AT 082330Z
   CIMSS AIDT: 78 KTS AT 082330Z
   CIMSS D-MINT: 71 KTS AT 082257Z
   CIMSS D-PRINT: 78 KTS AT 090110Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 27W IS EXPECTED TO TRACK ALONG THE
PERIPHERY OF THE CURRENT SUBTROPICAL STEERING RIDGE THROUGH THE 120
HOUR FORECAST PERIOD. THE SYSTEM WILL CONTINUE TO RAPIDLY INTENSIFY
OVER THE NEXT 24 HOURS ON ITS INITIALLY WEST-NORTHWESTWARD TREK
TOWARD THE STEERING RIDGE AXIS, SUPPORTED BY FAVORABLY LOW VERTICAL
WIND SHEAR, STRONG OUTFLOW ALOFT, AND PASSAGE OVER VERY WARM WATER.
THEREAFTER, THE SYSTEM IS EXPECTED TO LOSE ITS EQUATORWARD OUTFLOW
TAP AND MOVE UNDER THE PERIPHERAL FLOW OF UPPER-LEVEL RIDGING TO
THE NORTH, INTRODUCING MUTED BUT LESS FAVORABLE UNIDIRECTIONAL
ENVIRONMENTAL FLOW ALOFT THAT WILL HINDER ADDITIONAL
INTENSIFICATION AND AT FIRST AND INDUCE SLOW WEAKENING BY TAU 72.
ONCE THE SYSTEM  CRESTS THE RIDGE AXIS, IT WILL ACCELERATE
POLEWARD, WEAKEN DUE TO  PASSAGE OVER COOLER WATER, AND BEGIN
EXTRATROPICAL TRANSITION AS IT INTERACTS WITH A MID-LATITUDE TROUGH
DEVELOPING TO THE NORTHWEST.

MODEL DISCUSSION: NUMERICAL MODEL TRACK FORECAST GUIDANCE SHOWS A
SIMILAR PATTERN TO THE PREVIOUS CYCLE. ONCE AGAIN, ALL GUIDANCE IS
IN GOOD AGREEMENT WITH THE OVERALL STEERING SCENARIO, BUT SPREAD
INCREASES AFTER TAU 72. THE AI-BASED MODELS, GFS, AND ECMWF LIE
WITHIN A GROUPING THE BRACKETS THE WESTERN SIDE OF ENVELOPE AND THE
REMAINDER OF PHYSICS-BASED CONSENSUS MODELS LIE FARTHER TO THE
EAST. THE WESTERN GROUPING REPRESENTS A SCENARIO IN WHICH THE
STEERING RIDGE AMPLIFIES FARTHER POLEWARD AHEAD OF AN APPROACHING
MID-LATITUDE TROUGH IN THE EXTENDED RANGE THAN PREDICTED BY THE
EASTERN SOLUTIONS. THE CURRENT JTWC TRACK AGAIN FAVORS THE 
GFS-ECMWF-AI GROUPING AND IS CONSISTENT WITH THE PREVIOUS FORECAST
WITH HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE
THEREAFTER. INTENSITY FORECAST GUIDANCE IS IN VERY GOOD AGREEMENT
REGARDING NEAR-TERM RAPID INTENSIFICATION AND STEADY WEAKENING IN
THE EXTENDED PERIOD. THE CURRENT INTENSITY FORECAST IS ALSO
CONSISTENT WITH THE PREVIOUS JTWC FORECAST AND CONSENSUS INTENSITY 
GUIDANCE, BUT ONLY WITH MEDIUM CONFIDENCE DUE TO UNCERTAINTY 
REGARDING THE RATE OF NEAR-TERM INTENSIFICATION AND FINAL PEAK 
INTENSITY.

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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