Advisories

WDPN33 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.7N 159.0E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 774 NM EAST-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
27W (KOGUMA) WITH A RAPIDLY IMPROVING CENTRAL DENSE OVERCAST (CDO)
THAT IS NOW COMPLETELY OBSCURING THE LOW-LEVEL CIRCULATION CENTER
(LLCC). AROUND 081400Z, THE CONVECTION ACTUALLY APPEARS TO BE
TIGHTLY WRAPPING AROUND A DEVELOPING EYE. A 081112Z METOP-C ASCAT
SCATTEROMETER PASS REVEALED A COMPACT INNER-CORE WITH THE STRONGEST
WINDS PLACED WITHIN THE EASTERN SEMICIRCLE. THE INITIAL POSITION
AND WIND RADII ARE BOTH PLACED WITH HIGH CONFIDENCE BASED ON THE
TIMELY ASCAT DATA. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE ASCAT DATA ALONG WITH THE AGENCY
DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED BELOW.
ENVIRONMENTAL ANALYSIS INDICATES THAT 27W REMAINS PLACED WITHIN A
HIGHLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG OUTFLOW
ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA
SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 081112Z METOP-C ASCAT SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   PHFO: T4.5 - 77 KTS
   CIMSS ADT: 59 KTS AT 081210Z
   CIMSS AIDT: 51 KTS AT 081210Z
   CIMSS D-MINT: 64 KTS AT 081107Z
   CIMSS D-PRINT: 58 KTS AT 081210Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 27W IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR
THROUGH TAU 60. THE SYSTEM WILL THEN TURN NORTHWARD AS IT TRAVERSES
THE WESTERN EXTENT OF THE STR THROUGH TAU 120. REGARDING INTENSITY,
27W IS FORECAST TO RAPIDLY INTENSIFY THROUGH TAU 48 TO A PEAK OF
AROUND 120 KTS AS THE ENVIRONMENT REMAINS HIGHLY FAVORABLE AND THE
CIRCULATION RETAINS ITS COMPACT SIZE. NEAR TAU 60, OCEAN HEAT
CONTENT WILL START TO DROP AND VERTICAL WIND SHEAR WILL BEGIN TO
INCREASE, INITIATING A WEAKENING TREND. BY TAU 96, 27W WILL
APPROACH THE 26 C SST ISOTHERM AND SOUTHWESTERLY SHEAR IS EXPECTED
TO INCREASE TO OVER 20 KTS, FURTHER SUPPORTING THE WEAKENING TREND.



MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH
TAU 72 WITH NO NOTABLE OUTLIERS PRESENT. THE CROSS-TRACK SPREAD AT
TAU 72 IS MEASURED TO BE ABOUT 170 NM, LENDING HIGH CONFIDENCE TO
THE JTWC TRACK FORECAST THROUGH THAT TIMEFRAME. AFTER TAU 72, THE
GUIDANCE STARTS TO DIVERGE DUE TO VARYING TRACK SPEEDS AROUND THE
RIDGE. HOWEVER, AGREEMENT AFTER TAU 72 IS IN MUCH BETTER AGREEMENT
THIS RUN COMPARED TO THE PREVIOUS ONE. THE GEFS ENSEMBLE MEAN AND
GALWEM ARE THE TWO FASTEST MODELS WHILE THE EC-AIFS AND JGSM ARE
THE SLOWEST. THE JTWC TRACK FORECAST IS PLACED NEAR THE CONSENSUS
THROUGH TAU 72 AND THEN CLOSER TO THE GOOGLE DEEPMIND ENSEMBLE MEAN
THROUGH TAU 120. INTENSITY GUIDANCE NEARLY UNANIMOUSLY AGREES ON
RAPID INTENSIFICATION THROUGH TAU 48 WITH PEAK INTENSITIES RANGING
FROM 105-135 KTS. GUIDANCE THEN ALSO AGREES ON WEAKENING FOLLOWING
TAU 48. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE
CONSENSUS THROUGHOUT THE FORECAST PERIOD. CONFIDENCE ON THE
INTENSITY FORECAST REMAINS MEDIUM DUE TO INHERENT UNCERTAINTIES
REGARDING RAPID INTENSIFICATION.

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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