Advisories

WDPN33 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.1N 157.7E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 706 NM EAST-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY 27W HAS STEADILY INTENSIFIED OVER THE PAST SIX HOURS AND
ENVIRONMENTAL CONDITIONS HAVE BECOME INCREASINGLY SUPPORTIVE OF
RAPID INTENSIFICATION. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A NASCENT EYE FEATURE BEGINNING TO DEVELOP WITHIN
AN INCREASINGLY ORGANIZED AND SYMMETRIC RING OF DEEP CONVECTION
AROUND THE CENTER. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON RECENT TIGHTLY CLUSTERED SATELLITE POSITION
FIXES FROM PGTW, RJTD, AND RCTP. THE INITIAL INTENSITY OF 75 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A CONSENSUS OF THE
SUBJECTIVE DVORAK AND AUTOMATED INTENSITY ESTIMATES LISTED BELOW.
THERE IS SOME UNCERTAINTY IN THE INITIAL INTENSITY, AND CONSEQUENT
SPREAD AMONG INDIVIDUAL INTENSITY ESTIMATES, GIVEN THE RAPID
STRUCTURAL CHANGES OBSERVED IN RECENT SATELLITE IMAGERY.

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: T4.0 - 65 KTS
   CIMSS SATCON: 63 KTS AT 081447Z
   CIMSS ADT: 59 KTS AT 081730Z
   CIMSS AIDT: 55 KTS AT 081730Z
   CIMSS D-MINT: 85 KTS AT 081832Z
   CIMSS D-PRINT: 75 KTS AT 081900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 WILL CONTINUE TO TRACK ALONG THE
PERIPHERY OF THE CURRENT SUBTROPICAL STEERING RIDGE THROUGH THE 120
HOUR FORECAST PERIOD, GRADUALLY TURNING POLEWARD AND EASTWARD AHEAD
OF A DEVELOPING MID-LATITUDE TROUGH AS IT ROUNDS THE RIDGE AXIS.
RAPID INTENSIFICATION IS VERY LIKELY IN THE NEAR-TERM WITH
FAVORABLY LOW VERTICAL WIND SHEAR, STRONG OUTFLOW ALOFT, PASSAGE
OVER VERY WARM WATER, AND A PRIMED STORM STRUCTURE SUPPORTING THE
TREND. BY TAU 72, ALONG-TRACK OCEAN HEAT CONTENT WILL BEGIN TO DROP
AND THE SYSTEM WILL FEEL THE EFFECTS OF INCREASING VERTICAL WIND 
SHEAR AND A LESS FAVORABLE OUTFLOW PATTERN, INITIATING A WEAKENING 
TREND. IN THAT EXTENDED PERIOD, THE SYSTEM WILL ACCELERATE POLEWARD 
AHEAD OF THE AFOREMENTIONED TROUGH AND BEGIN EXTRATROPICAL TRANSITION 
BY TAU 120. INTERACTION WITH THE TROUGH IS EXPECTED TO PROVIDE 
FAVORABLE BAROCLINIC SUPPORT, ENABLING THE SYSTEM TO MAINTAIN TYPHOON 
INTENSITY AS IT TRANSITIONS TO A MIDLATITUDE LOW.

MODEL DISCUSSION: NUMERICAL MODEL TRACK FORECAST TRENDS ARE
CONSISTENT WITH THE PREVIOUS CYCLE. WHILE ALL GUIDANCE IS IN GOOD
AGREEMENT WITH THE OVERALL STEERING SCENARIO, SPREAD INCREASES
AFTER TAU 72. THE CONSENSUS OF PHYSICS-BASED MODELS DEPICTS A
TIGHTER TURN TOWARD THE NORTH-NORTHEAST THAN THE AI-BASED
CONSENSUS. HOWEVER, BOTH THE LATEST ECMWF AND GFS SOLUTIONS LIE
MORE IN LINE WITH THE AI-MODEL GUIDANCE, AND THE FULL GROUPING OF
THE GFS, ECMWF, AND AI-MODELS REPRESENT 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
OTHER SOLUTIONS. THE CURRENT JTWC TRACK FORECAST 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 MUTED WEAKENING IN
THE EXTENDED PERIOD, CONSTRAINING THE RANGE OF POSSIBLE OUTCOMES.
HOWEVER, THERE IS UNCERTAINTY IN THE RATE OF INTENSIFICATION AND 
FINAL PEAK INTENSITY. THE CURRENT INTENSITY FORECAST STAYS THE 
COURSE, CONSISTENT WITH THE PREVIOUS FORECAST, WITH MEDIUM 
CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
NNNN