WDPN31 PGTW 040900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (YAGI) WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.2N 117.4E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 258 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN OMINOUS
PINHOLE EYE FEATURE THAT HAS DEVELOPED IN PARALLEL WITH THE RAPID
INTENSIFICATION THAT HAS OCCURED OVER THE LAST 24 HOURS. WATER
VAPOR IMAGERY REVEALS STRONG EQUATORWARD OUTFLOW INTO A REGION OF
UPPER-LEVEL DIFFLUENCE AND WEAK EASTWARD OUTFLOW INTO AN
UPPER-LEVEL TROUGH.  THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON A 040547Z GCOM W1 AMSR2 PASS WHICH DEPICTS A
MICROWAVE EYE FEATURE ON BOTH THE 89GHZ AND 36GHZ IMAGES ALONGSIDE
THE AFOREMENTIONED ANIMATED MSI. THE INITIAL INTENSITY OF 80 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE
FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T4.5 - 77 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 81 KTS AT 040512Z
   CIMSS ADT: 79 KTS AT 040530Z

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: 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: TYPHOON (TY) 12W WILL CONTINUE TO BE DRIVEN
WEST-NORTHWESTWARD THROUGHT THE END OF THE FORECAST PERIOD WHILE
UNDER THE STEERING INFLUENCE OF THE STR TO THE NORTH, PASSING OVER
NORTHERN HAINAN AND THE LUICHOW PENINSULA SHORTLY AFTER TAU 48 AND
MAKING LANDFALL IN VIETNAM JUST PRIOR TO TAU 72. RAPID
INTENSIFICATION WILL CONTINUE WHILE IN THE WARM TUB OF THE SOUTH
CHINA SEA WITH A HIGH OCEAN HEAT CONTENT, STRONG UPPER-LEVEL
DIVERGENCE, AND LOW SHEAR THAT WILL CONTINUE UNTIL TAU 48. AFTER
TAU 48, THE SHEAR WILL BECOME MODERATE AS THE SYSTEM APPROACHES THE
COAST AND WILL WEAKEN DUE TO TOPOGRAPHIC INTERACTION. WEAKENING
WILL BECOME EVEN MORE DRASTIC AFTER MAKING LANDFALL JUST PRIOR TO
TAU 72 LEADING TO FULL DISSIPATION WHILE PASSING OVER THE
MOUNTAINOUS TERRAIN OF NORTHERN VIETNAM, LAOS, AND MYANMAR.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL TRACK WEST-NORTHWESTWARD THROUGH TAU 96. THE
MODEL TRACKERS ONLY APPEAR TO STRUGGLE AFTER TY 12W PASSES OVER THE
TALL MOUNTAINOUS TERRAIN, WHICH WILL CAUSE THE VORTEX TO SHALLOW
AND BECOME DIFFICULT TO TRACK AND PREDICT. THE INTENSITY GUIDANCE
IS IN MODERATE AGREEMENT THAT A PEAK WILL OCCUR AT TAU 36 BEFORE
CONSISTENT WEAKENING, BUT SOME OF THE JTWC CONSENSUS MEMBERS
FORECAST A PEAK AS LOW AS 90KTS (GFS) OR AS HIGH AS 135KTS (RICN
AND RIPA). 

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