Advisories

WDPN33 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.4N 151.5E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 218 NM SOUTHWEST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
27W (KORUMA) RECOVERING FROM ITS EARLIER EYEWALL REPLACEMENT CYCLE
(ERC), WITH ITS EYE CONTRACTING BY 10 NM OVER THE PAST 6 HOURS. THE
EYE REMAINS LARGE, BUT NOW MEASURES APPROXIMATELY 35 NM IN
DIAMETER. THE 091946Z RCM-3 SAR REVEALS A COMPACT AND SYMMETRICAL
WIND FIELD. ENVIRONMENTAL ANALYSIS REVEALS A HIGHLY FAVORABLE
ENVIRONMENT, CHARACTERIZED BY LOW (0-5 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 HIGH
CONFIDENCE BASED ON THE LARGE, PROMINENT EYE IN ANIMATED MSI. THE
INITIAL INTENSITY OF 110 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON EXTRAPOLATION FROM THE EARLIER SAR DATA, SUPPLEMENTED BY
THE AGENCY DVORAK FIXES AND AUTOMATED CIMSS INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: 091946Z RCM-3 SAR DATA

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


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.5 - 102 KTS
   CIMSS SATCON: 101 KTS AT 092230Z
   CIMSS ADT: 104 KTS AT 100110Z
   CIMSS AIDT: 100 KTS AT 092330Z
   CIMSS D-MINT: 101 KTS AT 092238Z
   CIMSS D-PRINT: 109 KTS AT 100110Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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 IS FORECAST TO CONTINUE TRACKING
NORTHWESTWARD WHILE IT REMAINS ON THE SOUTHWESTERN FLANK OF THE
STEERING RIDGE. FROM TAU 24-48, 27W WILL ROUND THE RIDGE AXIS AND
RECURVE TO THE NORTHEAST. 27W IS FORECAST TO BEGIN EXTRATROPICAL
TRANSITION NO LATER THAN TAU 72 AND COMPLETE TRANSITION BY TAU 96.
REGARDING INTENSITY, 27W IS FORECAST TO CONTINUE INTENSIFYING WHILE
THE ENVIRONMENT REMAINS CONDUCIVE, REACHING ITS PEAK INTENSITY
BETWEEN TAU 12-24. 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 48, 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 36-48. FROM TAU 48
ONWARD, KOGUMA IS FORECAST TO STEADILY 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. BY TAU 96, THE CROSS-TRACK SPREAD
INCREASES DUE TO A FEW EQUATORWARD OUTLIERS (NAVGEM 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 72-96. 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: LOW//
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