Advisories

WDPN33 PGTW 101500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.9N 149.6E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 510 NM NORTH-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 46 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 27W MAINTAINS AN IMPRESSIVE SATELLITE PRESENTATION,
WITH A WELL-DEFINED, CIRCULAR EYE MEASURING 25 NM IN DIAMETER
EMBEDDED IN A NEARLY SYMMETRIC CENTRAL DENSE OVERCAST (CDO). THE
EYE TEMPERATURE HAS RISEN TO 21 DEGREES CELSIUS, ITS WARMEST
OBSERVED VALUE, AND THE CDO CLOUD TOP TEMPERATURES REMAIN UNIFORMLY
BETWEEN -60 AND -70 DEGREES CELSIUS. UPPER-LEVEL OUTFLOW HAS
EXPANDED OVER THE PAST SIX HOURS. COINCIDENT SAR PASSES AT
APPROXIMATELY 100800Z FROM SENTINEL-1C AND RCM-3 ESTIMATED PEAK
SUSTAINED WINDS OF APPROXIMATELY 115-125 KTS, THOUGH THE RCM-3 PASS
INCLUDED A PEAK VALUE OF 135 KTS. WITH THE SATELLITE PRESENTATION
IMPROVED OVER THE PAST SIX HOURS, THE INITIAL INTENSITY HAS BEEN
RAISED TO 120 KTS WITH MEDIUM CONFIDENCE, SUPPORTED BY THE T6.0
DVORAK FIXES FROM PGTW AND RJTD AND OBJECTIVE ESTIMATES FROM CIMSS,
WHICH RANGE FROM 112 KTS TO 121 KTS. THE HIGHER RCM-3 VALUE
SUGGESTS THAT THE INITIAL INTENSITY MAY BE CONSERVATIVE, BUT IS NOT
FULLY CORROBORATED BY THE LOWER SENTINEL-1C AND THE REMAINING
SATELLITE ESTIMATES. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE CLEAR EYE. THE ENVIRONMENT IS FAVORABLE,
CHARACTERIZED BY LOW VERTICAL WIND SHEAR (VWS), WARM SEA SURFACE
TEMPERATURES (SST) OF 28-29 DEGREES CELSIUS, AND MODERATE
DIVERGENCE ALOFT.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 31N 168E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.5 - 102 KTS
   CIMSS SATCON: 114 KTS AT 100540Z
   CIMSS ADT: 112 KTS AT 101140Z
   CIMSS AIDT: 114 KTS AT 101140Z
   CIMSS D-MINT: 118 KTS AT 100936Z
   CIMSS D-PRINT: 121 KTS AT 101140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL

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 WILL TRAVEL NORTHWESTWARD AT 10 KTS
ALONG THE SOUTHWESTERN PERIPHERY OF A STR. THE SYSTEM WILL
GRADUALLY TURN POLEWARD AS IT REACHES THE WESTERN PERIPHERY OF THE
RIDGE, CROSS THE STR AXIS AFTER TAU 24, AND ACCELERATE
NORTHEASTWARD THEREAFTER, BECOMING INCREASINGLY EMBEDDED IN
DEEP-LAYER MID-LATITUDE WESTERLY FLOW. TY 27W IS LIKELY AT OR NEAR
PEAK INTENSITY, THOUGH SLIGHT ADDITIONAL INTENSIFICATION IS
POSSIBLE THROUGH TAU 12. WHILE VWS WILL REMAIN LOW AT 5-10 KTS
THROUGH TAU 36, THE SYSTEM HAS ABOUT 12 HOURS REMAINING OVER A
SUFFICIENTLY WARM SUBSURFACE WATER LAYER WITH OCEAN HEAT CONTENT
(OHC) OF 30 KJ PER CM2. AFTER TAU 12, THE CIRCULATION WILL TRAVERSE
THE COLD WAKES LEFT BEHIND BY FORMER TY 26W AND TS 15E. THESE LESS
FAVORABLE OCEAN CONDITIONS, COMBINED WITH RELATIVELY SLOW FORWARD
MOTION, WILL SUPPORT THE ONSET OF WEAKENING NEAR TAU 24. VWS WILL
BEGIN TO INCREASE AFTER TAU 36 AS THE SYSTEM GAINS LATITUDE AND
APPROACHES THE SOUTHERN PERIPHERY OF AN UPPER-LEVEL JET STREAM,
REACHING 40-50 KTS BY TAU 72. THE COMBINATION OF COOLER WATERS AND
STRONGER SHEAR WILL LEAD TO A MORE PRONOUNCED WEAKENING TREND. THE
STORM WILL BEGIN EXTRATROPICAL TRANSITION (ETT) BY TAU 96 AS IT
ENTERS A STRONGER BAROCLINIC ENVIRONMENT AND COMPLETE ETT BY TAU
120.

MODEL DISCUSSION: TRACK GUIDANCE IS IN EXCELLENT AGREEMENT, WITH
CROSS-TRACK SPREAD OF 40 NM AT TAU 36 AND 90 NM AT TAU 72. GFS AND
THE GEFS ENSEMBLE MEAN REMAIN THE MOST POLEWARD SOLUTIONS, WHILE
NAVGEM AND GALWEM ARE THE MOST EQUATORWARD. THE JTWC FORECAST TRACK
IS VIRTUALLY UNCHANGED FROM THE LAST FORECAST AND PLACED WITH HIGH
CONFIDENCE ALONG THE TIGHTEST MODEL CLUSTERING, WHICH IS NEARLY
CENTERED WITHIN THE GUIDANCE ENVELOPE AND CLOSEST TO THE
MULTI-MODEL CONSENSUS (CONW), ECMWF, AND GOOGLE DEEPMIND. MOST
INTENSITY AIDS DEPICT A WEAKENING TREND NO LATER THAN TAU 12.
COAMPS-TC AND DEEPMIND SHOW SLIGHT WEAKENING BY TAU 12, FOLLOWED BY
MORE RAPID WEAKENING, WHILE HAFS-A DELAYS ONSET OF WEAKENING BY 12
HOURS AND MAINTAINS A HIGHER INTENSITY THROUGHOUT THE FORECAST
PERIOD. THE JTWC INTENSITY FORECAST LIES AT THE UPPER END OF THE
GUIDANCE ENVELOPE, ALIGNED WITH HAFS-A THROUGH TAU 24, AND THEN
QUICKLY APPROACHES THE WEAKER GFS AND DEEPMIND SOLUTIONS BY TAU 60.

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