WDPN31 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (YAGI) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.2N 116.9E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 240 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A STRONG
TYPHOON WITH AN EYE FEATURE THAT HAS A CHARACTERISTIC TROCHOIDAL
WOBBLE AS THE SYSTEM HAS UNDERGONE RAPID INTENSIFICATION OVER THE
LAST SIX HOURS. UPPER-LEVEL OUTFLOW REMAINS STRONG AND EQUATORWARD
INTO A REGION OF UPPER-LEVEL DIFFLUENCE TO THE SOUTHWEST. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
AFOREMENTIONED EIR AND A RCM-2 SYNTHETIC APERTURE RADAR (SAR) IMAGE
FROM 041025Z. THE INITIAL INTENSITY OF 110 KTS IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE AFOREMENTIONED SAR IMAGE SUPPLEMENTED
BY THE AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: AMSR2 DATA

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T4.5 - 77 KTS
   KNES: T6.0 - 115 KTS
   CIMSS ADT: 109 KTS AT 041330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 31-32 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE CURRENT INTENSITY IS HIGHER THAN
PREVIOUSLY FORECASTED DUE TO RAPID INTENSIFICATION, AND THE PEAK IS
NOW EXPECTED TO BE 135KTS BY TAU 24.

FORECAST DISCUSSION: TYPHOON (TY) 12W IS FORECAST TO TRACK
WEST-NORTHWESTWARD WHILE UNDER THE STEERING INFLUENCE OF A STR TO
THE NORTH. BY TAU 48, THE SYSTEM IS EXPECTED TO PASS OVER NORTHERN
HAINAN AND THE LUICHOW PENINSULA BEFORE ENTERING THE GULF OF TONKIN
AND MAKING LANDFALL OVER NORTHERN VIETNAM. THE CURRENT TREND OF
RAPID INTENSIFICATION IS FORECAST TO CONTINUE FOR THE NEXT 24 HOURS
TO A PEAK INTENSITY OF 135KTS WHILE REMAINING IN A HIGHLY FAVORABLE
ENVIRONMENT COMPRISED OF LOW VERTICAL WIND SHEAR, WARM SEA SURFACE
TEMPERATURES, AND STRONG UPPER-LEVEL OUTFLOW. HIGH OCEAN HEAT
CONTENT IN THE WARM TUB OF THE SOUTH CHINA SEA IS WHAT WILL TAKE
THE ENVIRONMENT OVER THE EDGE TO ALLOW THE SYSTEM TO RAPIDLY
INTENSIFY. WEAKENING WILL COMMENCE AS THE SYSTEM INTERACTS WITH THE
LUICHOW PENINSULA AND HAINAN AND CONTINUE AFTER MAKING LANDFALL IN
NORTHERN VIETNAM. THE NORTHERN EXTENT OF THE ANNAMITE MOUNTAIN
RANGE WILL CAUSE THE VORTEX TO SHALLOW AS IT PASSES OVER PEAKS
ABOVE 5000FT HIGH AND FULLY DISSIPATE BY TAU 96.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL TRACK WEST-NORTHWESTWARD UNDER THE STEERING
INFLUENCE OF THE STR TO THE NORTH. THE LARGEST SPREAD OCCURS AS THE
SYSTEM PASSES OVER THE ANNAMITE MOUNTAIN RANGE, BUT ONLY OPENS TO
250NM DUE TO VARYING MODEL SOLUTIONS INTERPRETING HOW THE SHALLOW
SYSTEM ACTS AFTER BECOMING SHREDDED BY THE MOUNTAIN RANGE. THE
INTENSITY GUIDANCE DOES HAVE A LARGER SPREAD, WITH MODELS SUCH AS
COAMPS-TC, HWRF, AND GFS SHOWING A WEAKENING TREND THAT IS NOT
REFLECTIVE OF THE CURRENT ENVIRONMENT. THE JTWC INTENSITY FORECAST
LIES ABOVE THE MULTI-MODEL CONSENSUS BASED ON THE STRONG SIGNAL
GIVEN BY THE RAPID INTENSIFICATION AIDS, WHICH AT THE HIGHEST
REFLECT A POTENTIAL PEAK OF 155KTS. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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