Advisories

WDPN33 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.7N 153.0E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 217 NM SOUTH-SOUTHWEST OF MINAMI TORI
SHIMA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 27W (KOGUMA) AS A PETITE SYSTEM WITH A VERY LARGE EYE
MEASURING APPROXIMATELY 40 NM IN DIAMETER. KOGUMA RECENTLY
COMPLETED AN EYEWALL REPLACEMENT CYCLE (ERC) AND IS BEGINNING TO
CONTRACT THE NOW-DOMINANT OUTER EYEWALL. THE 091444Z AMSR3 SUITE OF
IMAGES CONFIRMED THE ERC WAS COMPLETE, LEAVING AN ELONGATED
LOW-LEVEL MICROWAVE EYE FEATURE UNDER THE MASSIVE UPPER-LEVEL EYE.
ENVIRONMENTAL ANALYSIS REVEALS A FAVORABLE ENVIRONMENT,
CHARACTERIZED BY LOW (5-10 KTS) VERTICAL WIND SHEAR (VWS), WARM
(28-29 C) SEA SURFACE TEMPERATURES (SST), MARGINAL (50-75 KJ PER
CM SQUARED) OCEAN HEAT CONTENT (OHC), AND MODERATE EQUATORWARD
OUTFLOW. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON
THE LOW-LEVEL CIRCULATION CENTER PARTIALLY OBSCURED BY THE
UPPER-LEVEL CONVECTION. THE INITIAL INTENSITY OF 100 KTS IS
ASSESSED WITH LOW CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND
AUTOMATED CIMSS INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE FROM THE 090752Z RCM-3 SAR

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T5.0 - 90 KTS
   CIMSS SATCON: 90 KTS AT 091800Z
   CIMSS ADT: 87 KTS AT 091930Z
   CIMSS AIDT: 91 KTS AT 091930Z
   CIMSS D-MINT: 98 KTS AT 091609Z
   CIMSS D-PRINT: 99 KTS AT 091930Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: LOW
   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 IS FORECAST TO CONTINUE TRACKING
NORTHWESTWARD WHILE IT REMAINS ON THE SOUTHWESTERN FLANK OF THE
STEERING RIDGE. FROM TAU 36-60, 27W WILL ROUND THE RIDGE AXIS AND
RECURVE TO THE NORTHEAST. 27W IS FORECAST TO BEGIN EXTRATROPICAL
TRANSITION NO LATER THAN TAU 96 AND COMPLETE TRANSITION BY TAU 120.
REGARDING INTENSITY, 27W IS FORECAST TO CONTINUE INTENSIFYING WHILE
THE ENVIRONMENT REMAINS CONDUCIVE, REACHING ITS PEAK INTENSITY
AROUND TAU 24. FOLLOWING TAU 24, THE ENVIRONMENT IS EXPECTED TO
SLIGHTLY WORSEN, WITH VWS CREEPING HIGHER, SSTS AND OHC FALLING,
COUPLED WITH THE ONSET OF DRY AIR ENTRAINMENT. THESE FACTORS ARE
EXPECTED TO INITIATE THE TERMINAL WEAKENING TREND, WITH THE RATE
OF WEAKENING BEGINNING GRADUALLY. BY TAU 60, THE ENVIRONMENT IS
EXPECTED TO BE SIGNIFICANTLY WORSE, CHARACTERIZED BY INCREASING VWS
AND SIGNIFICANT DRY AIR ENTRAINMENT, COUPLED WITH COOL SSTS AND LOW
OHC AS 27W CROSSES THE 26C ISOTHERM BETWEEN TAU 60-72. FROM TAU 60
ONWARD, KOGUMA IS FORECAST TO SWIFTLY WEAKEN AS IT TRACKS POLEWARD
AND ULTIMATELY BECOMES AN EXTRATROPICAL SYSTEM. 

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH TAU 72, WITH MINOR FLUCTUATIONS IN ALONG-TRACK
AND CROSS-TRACK SPREADS. FOLLOWING TAU 72, THE CROSS-TRACK SPREAD
INCREASES DUE TO A FEW EQUATORWARD OUTLIERS (NAVGEM, GALWEM, AND
UKMET). DISREGARDING THOSE MEMBERS, THE MODEL ENVELOPE IS IN GOOD
AGREEMENT. THE JTWC TRACK FORECAST IS PLACED SLIGHTLY POLEWARD OF
THE MULTI-MODEL CONSENSUS TO COUNTERACT THE EFFECT OF THE OUTLIERS.
THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE FROM TAU
0-72 AND MEDIUM CONFIDENCE FROM TAU 72-120. RELIABLE INTENSITY AIDS
ARE IN POOR AGREEMENT, WITH SEVERAL MODELS STRUGGLING TO
INITIALIZE THE SYSTEM'S CURRENT INTENSITY. THE JTWC INTENSITY
FORECAST IS ALIGNED CLOSE TO THE HAFS-A SOLUTION WITH OVERALL
MEDIUM CONFIDENCE.

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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