Advisories

WDPN33 PGTW 111500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.2N 147.4E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 341 NM EAST-NORTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 44 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 27W CONTINUES TO WEAKEN AS IT TRACKS
NORTH-NORTHWESTWARD AT 10 KTS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS A CIRCULAR, CLEAR EYE MEASURING 20 NM IN
DIAMETER EMBEDDED IN A SYMMETRIC CENTRAL DENSE OVERCAST (CDO) WITH
MODERATE RADIAL OUTFLOW AND STRENGTHENING POLEWARD EXHAUST ALOFT.
THE CDO CLOUD TOP TEMPERATURES HAVE GRADUALLY WARMED AND BECOME
LESS UNIFORM, WHILE THE EYE TEMPERATURE HAS HELD STEADY AT 16-17
DEGREES CELSIUS. A 110811Z GMI PASS SHOWED A CONVECTIVE RING
SURROUNDING A DETERIORATING INNER EYEWALL, INDICATIVE OF AN ONGOING
EYEWALL REPLACEMENT CYCLE (ERC). TY 27W IS NOW MOVING OVER A TONGUE
OF COOLER SEA SURFACE TEMPERATURES (SST) OF 26-27 DEGREES CELSIUS
AND LOW OCEAN HEAT CONTENT (OHC) IN AN ENVIRONMENT OF LOW VERTICAL
WIND SHEAR (VWS). THE ERC, COUPLED WITH MARGINAL SST, IS RESULTING
IN A GRADUAL DEGRADATION OF THE CONVECTIVE STRUCTURE. THIS
DEGRADATION IS REFLECTED IN THE OBJECTIVE INTENSITY ESTIMATES FROM
CIMSS RANGING FROM 112 KTS TO 115 KTS AND THE PGTW FINAL T-NUMBER
OF T5.5 WITH A CURRENT INTENSITY OF T6.0. THEREFORE, THE INITIAL
INTENSITY IS LOWERED TO 110 KTS WITH MEDIUM CONFIDENCE. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED,
CLEAR EYE IN SHORTWAVE INFRARED IMAGERY.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 28N 167E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.0 - 115 KTS
   CIMSS ADT: 112 KTS AT 111130Z
   CIMSS AIDT: 114 KTS AT 111130Z
   CIMSS D-MINT: 115 KTS AT 111142Z
   CIMSS D-PRINT: 114 KTS AT 111130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE RADIAL

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: TY 27W WILL CONTINUE TO TURN POLEWARD ALONG
THE WESTERN PERIPHERY OF A DEEP-LAYER STR, CROSS THE RIDGE AXIS BY
TAU 24, AND THEN BEGIN TO ACCELERATE NORTHEASTWARD INTO THE
WESTERLY FLOW. AS THE SYSTEM GAINS SIGNIFICANT LATITUDE BETWEEN TAU
36 AND TAU 60, AN UPPER-LEVEL RIDGE WILL BUILD OVER KAMCHATKA,
SHIFTING THE MAIN JET CORE FARTHER NORTH. AS TY 27W ACCELERATES
POLEWARD, IT WILL REMAIN SOUTH OF THE JET CORE BUT PHASE WITH THE
RIGHT-FRONT ENTRANCE REGION OF A 130-KT JET STREAK BETWEEN TAU 24
AND TAU 60. THIS INTERACTION WILL ALLOW THE SYSTEM TO RETAIN
TROPICAL CHARACTERISTICS WELL INTO THE MID-LATITUDES. EXTRATROPICAL
TRANSITION (ETT) WILL BEGIN BY TAU 72 AND COMPLETE BY TAU 96.
STEADY WEAKENING WILL CONTINUE IN THE SHORT TERM AS TY 27W
UNDERGOES ERC AND TRAVERSES WATERS WITH MARGINAL SST AND LOW OHC
THROUGH TAU 24. THIS COOLER WATER IS ASSOCIATED WITH THE COLD WAKES
OF FORMER TY 26W AND 15E. THEREAFTER, THE VORTEX WILL CROSS THE
26-DEGREE CELSIUS ISOTHERM INTO MUCH COOLER WATERS. VWS WILL BEGIN
TO INCREASE AROUND TAU 24, REACHING 30-40 KTS BY TAU 48. THESE
CONDITIONS ALONE WOULD LEAD TO VERY RAPID WEAKENING. HOWEVER,
ENHANCED POLEWARD OUTFLOW ASSOCIATED WITH THE JET STREAK
INTERACTION WILL MODERATE THE RATE OF WEAKENING. THE FORECAST CALLS
FOR A SLOWER WEAKENING TREND NEAR THE END OF THE FORECAST PERIOD AS
THE SYSTEM BROADENS AND UNDERGOES ETT.

MODEL DISCUSSION: TRACK GUIDANCE REMAINS TIGHT, WITH A CROSS-TRACK
SPREAD OF 40 NM AT TAU 24, 80 NM AT TAU 48, AND 170 NM AT TAU 72.
THE ALONG-TRACK SPREAD IS MINIMAL, WITH ECMWF AND NAVGEM AHEAD OF
THE REST OF THE GUIDANCE BY 80 NM AT TAU 96. GFS, ECMWF, JGSM, AND
GOOGLE DEEPMIND LIE NEAR THE CORE CLUSTER, WHICH IS CENTERED WITHIN
THE GUIDANCE ENVELOPE AND INCLUDES THE MULTI-MODEL CONSENSUS (CONW)
AND THE AI-MODEL MEAN. THE JTWC FORECAST TRACK HAS SHIFTED POLEWARD
BY 20-40 NM FROM TAU 12 TO TAU 96 TO ALIGN WITH THIS CORE GROUP.
INTENSITY AIDS ARE ALSO IN EXCELLENT AGREEMENT WITH A 5 KT SPREAD
AMONG HAFS-A, COAMPS-TC, AND DEEPMIND. THE JTWC INTENSITY FORECAST
IS ALIGNED WITH THESE SOLUTIONS THROUGH TAU 96.

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