Advisories

WDPN33 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 030//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.8N 147.7E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 522 NM SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
27W SHAPED LIKE A DONUT WITH A LARGE EYE EMBEDDED IN A RELATIVELY
SYMMETRIC, COMPACT CENTRAL DENSE OVERCAST (CDO). FOLLOWING THE
COMPLETION OF AN EYEWALL REPLACEMENT CYCLE (ERC) 6-12 HOURS AGO,
THE EYE OF TY 27W DOUBLED IN SIZE TO A DIAMETER OF 40 NM. OVER THE
PAST 6 HOURS, THE EYE HAS BECOME MORE RAGGED AND CLOUD-FILLED, AND
THE CIRRUS CANOPY OVER THE CDO HAS BECOME LESS SMOOTH. CLOUD TOP
TEMPERATURES CONTINUE TO WARM, WHILE THE EYE TEMPERATURE COOLS. THE
VORTEX IS NOW SKIRTING THE 26-DEGREE CELSIUS ISOTHERM UNDER
MODERATE, SOUTHWESTERLY VERTICAL WIND SHEAR (VWS). UPPER-LEVEL
OUTFLOW IS BECOMING LESS RADIAL, WITH OUTFLOW ENHANCED ON THE
POLEWARD SIDE AND SUPPRESSED ON THE EQUATORWARD SIDE. BASED ON THE
DEGRADING SATELLITE PRESENTATION, THE INITIAL INTENSITY HAS BEEN
LOWERED TO 90 KTS WITH MEDIUM CONFIDENCE, SUPPORTED BY A BLEND OF
THE T4.5-5.5 DVORAK CLASSIFICATIONS FROM RCTP AND PGTW AND
OBJECTIVE ESTIMATES FROM CIMSS RANGING FROM 87 KTS TO 96 KTS. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE LARGE
EYE IN MSI.

INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 27N 164E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T4.5 - 77 KTS
   CIMSS SATCON: 95 KTS AT 120510Z
   CIMSS ADT: 87 KTS AT 120540Z
   CIMSS AIDT: 96 KTS AT 120540Z
   CIMSS D-MINT: 88 KTS AT 120343Z
   CIMSS D-PRINT: 88 KTS AT 120540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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: TY 27W HAS CROSSED THE STR AXIS AND IS NOW
ACCELERATING NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF THE
DEEP-LAYER RIDGE. AS THE SYSTEM GAINS LATITUDE, IT WILL COME UNDER
THE INFLUENCE OF THE SOUTHERN PERIPHERY OF THE UPPER-LEVEL JET. THE
ENVIRONMENT ALONG THE FORECAST TRACK WILL BECOME INCREASINGLY
HOSTILE, WITH SST FALLING BELOW 26 DEGREES CELSIUS BY TAU 24 AND
VWS INCREASING TO NEAR 30 KTS BY TAU 24 AND 40-50 KTS BY TAU 48-72.
THESE FACTORS WILL LEAD TO STEADY WEAKENING OVER THE NEXT 24 HOURS,
FOLLOWED BY A SLOWER RATE AS THE SYSTEM BROADENS OUT AND APPROACHES
A MORE BAROCLINIC ENVIRONMENT. THE SYSTEM WILL BEGIN EXTRATROPICAL
TRANSITION (ETT) BY TAU 60 AND COMPLETE ETT BY TAU 72.

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT, WITH A
CROSS-TRACK SPREAD OF 55 NM AT TAU 24, 115 NM AT TAU 48, AND 165 NM
AT TAU 72. THE ALONG-TRACK SPREAD IS SMALL, AT LESS THAN 100 NM AT
TAU 72. ECMWF IS THE MOST POLEWARD MODEL, WHILE GALWEM AND UKMET
ARE THE MOST EQUATORWARD. THE JTWC FORECAST TRACK IS PLACED WITH
HIGH CONFIDENCE NEAR THE CENTER OF THE GUIDANCE ENVELOPE, ALIGNING
WITH THE MULTI-MODEL CONSENSUS AND GOOGLE DEEPMIND. SIMILARLY, THE
INTENSITY GUIDANCE IS TIGHTLY PACKED. THE JTWC INTENSITY FORECAST
IS SET NEAR DEEPMIND, COAMPS-TC, AND GFS THROUGH TAU 36 AND THEN
LEANS TOWARD GFS FROM TAU 36 TO TAU 72.

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