WDPN31 PGTW 051500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (YAGI) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3N 114.1E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 473 NM EAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 52 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON 12W HAS WEAKENED SLIGHTLY WHILE UNDERGOING AN EYEWALL
REPLACEMENT CYCLE (ERC) AS PREDICTED BY THE CIMSS M-PERC PRODUCT.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A 20NM
ROUND EYE, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. 
AFTER 051200Z, EIR IMAGERY DOES INDICATE A STRENGTHENING EYEWALL WITH 
COOLING CLOUD TOP TEMPERATURES, WHICH COULD LEAD TO A SLIGHT 
INTENSIFICATION OVER THE NEXT SIX HOURS OR SO. A 051046Z SSMIS
91GHZ MICROWAVE IMAGE SHOWS THAT THE SMALL INNER EYEWALL HAS
REMAINED INTACT, WITH THE OUTER EYEWALL WEAKENING OVER THE SOUTHWEST 
QUADRANT. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE WITH RADIAL 
OUTFLOW AND LOW VERTICAL WIND SHEAR THUS, THE CURRENT WEAKENING TREND 
IS SOLELY ATTRIBUTED TO THE ERC. THE INITIAL INTENSITY OF 120 KTS IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON A 051033Z RCM-2 SAR IMAGE 
SHOWING A MAXIMUM WIND OF 120 KNOTS. WIND RADII HAVE BEEN ADJUSTED 
BASED ON THIS SAR IMAGE.

INITIAL WIND RADII BASIS: RCM-2 SAR DATA 

CURRENT STEERING MECHANISM: STRONG SUBTROPICAL RIDGE (STR)
ENTRENCHED OVER CENTRAL AND EASTERN CHINA.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T7.0 - 140 KTS 
   KNES: T6.5 - 127 KTS
   CIMSS ADT: 107 KTS AT 051130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: WHILE ENVIRONMENTAL CONDITIONS REMAIN
FAVORABLE OVER THE NEXT 06-12 HOURS, SOME RE-INTENSIFICATION IS
POSSIBLE AFTER THE ERC COMPLETES. AFTER TAU 12, THE SYSTEM WILL
TRACK WESTWARD APPROACHING HAINAN ISLAND, WITH A MORE PRONOUNCED
WEAKENING TREND DUE TO INTERACTION WITH LAND. AFTER TAU 24, RAPID
WEAKENING WILL OCCUR AS THE SYSTEM TRACKS OVER SOUTHERN CHINA AND
NORTHERN VIETNAM, WITH LANDFALL EXPECTED NEAR TAU 48. AS THE SYSTEM
TRACKS INTO THE RUGGED TERRAIN OF NORTHERN VIETNAM, IT WILL
DISSIPATE BY TAU 72. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE USED IN THE JTWC
CONSENSUS (CONW) REMAINS IN TIGHT AGREEMENT WITH A 35-45NM
CROSS-TRACK SPREAD FROM TAU 36 TO TAU 48. PROBABILISTIC GUIDANCE
FROM THE ECMWF (EPS) AND GFS (GEFS) ENSEMBLES ALSO REMAINS IN TIGHT
AGREEMENT SUPPORTING THE JTWC TRACK FORECAST WITH HIGH CONFIDENCE.
RELIABLE INTENSITY GUIDANCE IS ALSO IN VERY GOOD AGREEMENT
SUPPORTING THE RAPID WEAKENING PHASE EXPECTED AFTER TAU 24.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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