Advisories

WDPN33 PGTW 122100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 032//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.2N 149.6E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 492 NM NORTHEAST OF CHICHI JIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 27W (KOGUMA) WITH AN ASYMMETRICAL CONVECTIVE STRUCTURE AND
NEARLY ALL CONVECTION CONFINED TO THE NORTHERN SEMICIRCLE. THE
SYSTEM REMAINS TILTED NORTHEASTWARD WITH HEIGHT, AS THE LOW LEVEL
CIRCULATION CENTER (LLCC) REMAINS MOSTLY OBSCURED BY THE DISPLACED
CENTRAL DENSE OVERCAST (CDO), BUT IS INTERMITTENTLY VISIBLE WITHIN
THE RAGGED MID-LEVEL CIRCULATION. ENVIRONMENTAL CONDITIONS ARE
HIGHLY UNFAVORABLE AS TY 27W EXPERIENCES HIGH (25-30 KTS)
SOUTHWESTERLY VERTICAL WIND SHEAR (VWS) CAUSING DRY AIR ENTRAINMENT 
AND FURTHER VORTEX TILT, AS WELL AS BEING WITHIN 25-26 C SEA SURFACE 
TEMPERATURES (SSTS). THE INITIAL POSITION IS PLACED WITH MEDIUM 
CONFIDENCE BASED ON THE PARTIALLY OBSCURED LLCC IN EIR IMAGERY. THE 
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE 
SPREAD OF AGENCY DVORAK FIXES AND OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.5 - 77 KTS
   CIMSS SATCON: 78 KTS AT 121606Z
   CIMSS ADT: 65 KTS AT 121730Z
   CIMSS AIDT: 67 KTS AT 121730Z
   CIMSS D-MINT: 70 KTS AT 121606Z
   CIMSS D-PRINT: 63 KTS AT 121730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 25-30 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 IS FORECAST TO CONTINUE ACCELERATING
NORTHEASTWARD UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTHEAST FOR THE REMAINDER OF THE FORECAST PERIOD.
EXTRATROPICAL TRANSITION (ETT) IS EXPECTED TO BEGIN BY TAU 36, AS
27W NEARS THE UPPER-LEVEL JET AND BEGINS INTERACTING WITH THE
BAROCLINIC ZONE, COMPLETING ETT NO LATER THAN TAU 60. REGARDING
INTENSITY, KOGUMA IS EXPECTED TO STEADILY WEAKEN FOR THE REMAINDER
OF THE FORECAST PERIOD, DESPITE THE INCREASED POLEWARD OUTFLOW
ALOFT DUE TO INTERACTION WITH THE STRONG UPPER-LEVEL WESTERLIES, AS
THE REMAINDER OF ENVIRONMENTAL CONDITIONS WILL BECOME INCREASINGLY
HOSTILE, WITH VWS EXPECTED TO EXCEED 40 KTS BY TAU 36, INCREASING
DRY AIR ENTRAINMENT AND VORTEX TILT. HOWEVER, THE SYSTEM IS
EXPECTED TO BE AT TROPICAL STORM STRENGTH AT THE TIME OF ETT.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THE
REMAINDER OF THE FORECAST PERIOD WITH A CROSS-TRACK SPREAD OF 120
NM AND AN ALONG-TRACK SPREAD OF 150 NM AT TAU 60, ALTHOUGH REMOVING
THE SLOWEST AND FASTEST OUTLIERS OF GALWEM AND NAVGEM WOULD
DECREASE ALONG-TRACK SPREAD TO ONLY 40 NM. THUS, THE OFFICIAL JTWC
FORECAST TRACK IS PLACED WITH HIGH CONFIDENCE, CLOSELY IN LINE WITH
THE MULTI-MODEL CONSENSUS AND GOOGLE DEEPMIND. INTENSITY GUIDANCE
IS ALSO IN GOOD AGREEMENT, WITH THE ONLY OUTLIERS BEING COAMPS-TC
(BOTH GFS AND NAVGEM BASED) DEPICTING A MUCH STEEPER WEAKENING
TREND AFTER TAU 24 THAN THE REST OF THE GUIDANCE PACKAGE. OVERALL,
THE OFFICIAL JTWC INTENSITY FORECAST IS ASSESSED WITH HIGH
CONFIDENCE, CLOSELY IN LINE WITH THE MULTI-MODEL GUIDANCE OUT TO
TAU 36 AND SLIGHTLY ABOVE IT THEREAFTER IN LINE WITH HAFS-A AND
GOOGLE DEEPMIND.

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