WDPN31 PGTW 061500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (YAGI) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.0N 110.2E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 249 NM EAST-SOUTHEAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 12W MADE LANDFALL OVER NORTHERN HAINAN ISLAND AT ABOUT 
060800Z, TRACKING ALONG THE NORTHERN COAST DIRECTLY OVER HAIKOU 
(ZJHK), WHICH REPORTED MAXIMUM SUSTAINED NORTH-NORTHWESTERLY WINDS 
(10-MINUTE AVERAGE) OF 70 KNOTS GUSTING TO 95 KNOTS WITH MINIMUM SLP 
NEAR 928MB. AFTER PASSING OVER HAIKOU, THE SURFACE WINDS SWITCHED 
QUICKLY TO A SOUTHERLY DIRECTION AT 49 KNOTS GUSTING TO 74 KNOTS. AS 
INDICATED IN ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY, THE 
EYE CONTRACTED QUICKLY WHILE THE OVERALL CONVECTIVE STRUCTURE 
WEAKENED. OVERALL, THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION 
BASED ON RADAR IMAGERY, EIR IMAGERY AND SURFACE OBSERVATIONS. THE 
INITIAL INTENSITY IS ASSESSED AT 120 KNOTS, WHICH IS CONSISTENT WITH 
THE STANDARD WIND PRESSURE RELATIONSHIP CORRESPONDING TO 928MB. 
ADDITIONALLY, THIS IS SUPPORTED BY THE PGTW AND KNES DVORAK CURRENT 
INTENSITY ESTIMATES. 

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T5.5 - 102 KTS
   KNES: T6.5 - 127 KTS
   DEMS: T5.5 - 102 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: LAND INTERACTION

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 12W IS FORECAST TO TRACK WESTWARD TO WEST-
NORTHWESTWARD THROUGH THE FORECAST PERIOD. WITH THE EXCEPTION OF THE 
LAND INTERACTION, RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR COUPLED 
WITH WARM SST VALUES SHOULD SUPPORT A STRONG TYPHOON STRENGTH SYSTEM 
OVER THE NEXT 12 HOURS. AFTER TAU 12, TY 12W WILL WEAKEN SLOWLY AS IT 
APPROACHES VIETNAM, WITH LANDFALL OVER NORTHERN VIETNAM EXPECTED NEAR 
TAU 24. AS THE SYSTEM TRACKS INTO NORTHERN VIETNAM AND LAOS, IT WILL 
WEAKEN RAPIDLY AND DISSIPATE BY TAU 72. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE USED IN THE JTWC
CONSENSUS (CONW) REMAINS IN TIGHT AGREEMENT WITH A 35NM CROSS-TRACK 
SPREAD AT TAU 24. 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 12.

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