Advisories

WDPN33 PGTW 102100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 024//
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:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 27W (KOGUMA) AS A VIGOROUS, COMPACT, AND SYMMETRICAL SYSTEM
WITH AN EYE MEASURING APPROXIMATELY 20 NM IN DIAMETER. THE 101844Z
SUITE OF GMI IMAGES REVEALS THE STORM IS GEARING UP FOR A SECOND
EYEWALL REPLACEMENT CYCLE (ERC), WITH A PARTIAL OUTER EYEWALL
BEGINNING TO FORM ABOUT 40 NM FROM THE CENTER. ENVIRONMENTAL
ANALYSIS REVEALS A HIGHLY FAVORABLE ENVIRONMENT, CHARACTERIZED BY
LOW (0-5 KTS) VERTICAL WIND SHEAR (VWS), WARM (27-28 C) SEA SURFACE
TEMPERATURES (SST), GOOD (50-75 KJ PER CM SQUARED) OCEAN HEAT
CONTENT (OHC), AND STRONG RADIAL OUTFLOW. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED EYE IN
ANIMATED EIR. THE INITIAL INTENSITY OF 120 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE GOOD AGREEMENT OF THE AGENCY DVORAK
FIXES AND THE CIMSS AUTOMATED INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.5 - 102 KTS
   CIMSS SATCON: 121 KTS AT 101830Z
   CIMSS ADT: 109 KTS AT 101800Z
   CIMSS AIDT: 115 KTS AT 101800Z
   CIMSS D-MINT: 117 KTS AT 101840Z
   CIMSS D-PRINT: 117 KTS AT 101800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 TRACK
NORTH-NORTHWESTWARD FOR THE NEXT 12 HOURS WHILE IT REMAINS ON THE
SOUTHWESTERN PERIPHERY OF THE STEERING RIDGE. FOLLOWING TAU 12, 27W
WILL CURVE NORTHWARD AS IT BEGINS TO ROUND THE STR. KOGUMA IS
EXPECTED TO ROUND THE RIDGE AXIS AROUND TAU 24 AND RECURVE TO THE
NORTHEAST. 27W WILL MAINTAIN A NORTHEASTWARD TRACK FROM TAU 36
THROUGH THE END OF THE FORECAST. REGARDING INTENSITY, 27W IS
ASSESSED TO BE AT ITS PEAK INTENSITY, AND IS EXPECTED TO GRADUALLY
WEAKEN FOR THE NEXT 36 HOURS AS THE ENVIRONMENT SLOWLY BECOMES LESS
FAVORABLE. BY TAU 36, VWS IS EXPECTED TO INCREASE TO 15-20 KTS
WHICH WILL INDUCE MID-LEVEL DRY AIR ENTRAINMENT. ADDITIONALLY, OHC
IS EXPECTED TO DROP TO 0 KJ PER CM SQUARED AS KOGUMA CROSSES THE
26C ISOTHERM AROUND TAU 36. HOWEVER, THE RATE OF WEAKENING FOR THE
NEXT 36 HOURS MAY BE INCREASED IF 27W ATTEMPTS A SECOND ERC AND
FAILS TO COMPLETE THE CYCLE. FOLLOWING TAU 36, 27W IS EXPECTED TO
RAPIDLY WEAKEN THROUGH TAU 72 AS THE ENVIRONMENT TURNS HOSTILE.
KOGUMA IS FORECAST TO ENCOUNTER 40-50 KTS OF VWS, SIGNIFICANT DRY
AIR ENTRAINMENT, COLD (LESS THAN 24C) SSTS, AND SUPPRESSED OUTFLOW
CAUSED BY INCREASING PROXIMITY TO THE UPPER-LEVEL WESTERLIES. 27W
IS EXPECTED TO SKIRT THE EQUATORWARD FRINGES OF THE WESTERLIES
BETWEEN TAU 72-96, BEFORE FINALLY BECOMING EMBEDDED IN THE FLOW BY
TAU 120. AS A RESULT, KOGUMA IS FORECAST TO BEGIN EXTRATROPICAL
TRANSITION BY TAU 96 AND COMPLETE TRANSITION BY TAU 120.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH THE DURATION OF THE FORECAST PERIOD, THOUGH
NAVGEM, GALWEM, AND GSM ARE NOTABLE OUTLIERS. DISCOUNTING THOSE
MODELS, THE JTWC TRACK FORECAST IS PLACED WITH OVERALL HIGH
CONFIDENCE. RELIABLE INTENSITY AIDS ARE IN AGREEMENT IN A WEAKENING
TREND THROUGH TAU 120, BUT DISAGREE ON THE RATE OF WEAKENING. THE
JTWC INTENSITY FORECAST IS HEDGED SLIGHTLY HIGHER THAN THE
MULTI-MODEL CONSENSUS FROM TAU 0-36 DUE TO THE FAVORABLE
ENVIRONMENTAL CONDITIONS ANTICIPATED. HOWEVER, AS DISCUSSED ABOVE,
27W MAY WEAKEN FASTER THAN ANTICIPATED SHOULD IT ATTEMPT ANOTHER
ERC AND FAIL TO COMPLETE THE CYCLE PRIOR TO REACHING THE HIGHLY
UNFAVORABLE ENVIRONMENT EXPECTED AFTER TAU 36. THE JTWC INTENSITY
FORECAST IS IN ALIGNMENT WITH THE MULTI-MODEL CONSENSUS FROM TAU
72-120. AS A RESULT, THE JTWC INTENSITY FORECAST IS ASSESSED WITH
OVERALL MEDIUM CONFIDENCE.

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