WDPN32 PGTW 131500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (VAMCO) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 25W (VAMCO), LOCATED APPROXIMATELY 296 NM EAST OF DA 
NANG, VIETNAM, HAS TRACKED WESTWARD AT 10 KNOTS OVER THE PAST SIX 
HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) INDICATES 
THAT THE SYSTEM HAS UNDERGONE AN UNEXPECTED PERIOD OF RAPID 
INTENSIFICATION OVER THE PREVIOUS SIX HOURS, WITH DEEP CONVECTION 
DEVELOPING PARTICULARLY IN THE SOUTHWEST QUADRANT AND WRAPPING INTO A 
VERY WELL DEFINED, THOUGH SOMEWHAT RAGGED, 20NM WIDE EYE. THE INITIAL 
POSITION IS SET WITH HIGH CONFIDENCE BASED ON THE WELL DEFINED EYE IN 
THE EIR, SUPPORTED BY A 131216Z ASCAT-A BULLSEYE PASS. WIND RADII HAVE 
ALSO BEEN SIGNIFICANTLY EXPANDED BASED ON THE ASCAT DATA. THE INITIAL 
INTENSITY HAS BEEN INCREASED TO 100 KTS WITH FAIR CONFIDENCE BASED ON 
MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T6.0 (115 KNOTS) 
FROM PGTW, T5.0 (90 KNOTS) FROM RJTD AND T5.5 (102 KNOTS) FROM KNES, 
THOUGH SOMEWHAT LOWER THAN THE ADVANCED DVORAK TECHNIQUE (ADT) 
ESTIMATE OF T6.3, AND SATELLITE CONSENSUS ESTIMATE OF 110 KNOTS. TY 
VAMCO IS TRACKING WESTWARD ALONG THE SOUTHERN PERIPHERY OF A 
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. THE ENVIRONMENT 
HAS NOT CHANGED SIGNIFICANTLY, WITH THE SYSTEM TRACKING OVER WATERS AT 
OR JUST ABOVE 27 DEG CELSIUS, BUT WITH VERY LOW OCEAN HEAT CONTENT 
(OHC). THE UPPER-LEVEL PATTERN HAS HOWEVER CHANGED SIGNIFICANTLY, WITH 
THE UNEXPECTED DEVELOPMENT OF A SMALL BUT VERY POTENT POINT SOURCE 
DIRECTLY OVER THE SYSTEM WHICH HAS LED TO A ROBUST DUAL CHANNEL 
OUTFLOW PATTERN, DRAMATICALLY INCREASING THE EXHAUST MECHANISM AND 
ENABLING THE WITNESSED RAPID INTENSIFICATION. 
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST TRACK PHILOSOPHY, HOWEVER IN 
LIGHT OF THE RECENT RAPID INTENSIFICATION, THE FORECAST INTENSITIES 
HAVE BEEN SIGNIFICANTLY INCREASED THROUGH LANDFALL. 
   B. TY 25W WILL CONTINUE TO TRACK WEST TO WEST-NORTHWESTWARD THROUGH 
THE ENTIRETY OF THE FORECAST PERIOD UNDER THE STEERING INFLUENCE OF 
THE 
AFOREMENTIONED STR CENTERED TO THE NORTHEAST. ADDITIONAL NEAR-TERM (0-
12 HOURS) INTENSIFICATION IS POSSIBLE WHICH IS NOT CAPTURED BY THE 
FORECAST POINTS, AS THE SYSTEM REMAINS OVER WARM (26-27 DEG CELSIUS) 
WATERS AND THE UPPER-LEVEL POINT SOURCE CONTINUES TO PROVIDE ROBUST 
DUAL-CHANNEL OUTFLOW. HOWEVER, BY TAU 12, THE SYSTEM SHOULD WEAKEN 
SLIGHTLY AS THE POLEWARD OUTFLOW CHANNEL BEGINS TO BE IMPINGED, AND 
THE SYSTEM TRACKS OVER STEADILY COOLER WATERS. CURRENT SST 
MEASUREMENTS INDICATE SSTS DECREASE TO LESS THAN 26 DEG CELSIUS WEST 
OF THE 110 DEG LONGITUDE. BY TAU 24, THE SYSTEM WILL BE WEST OF THIS 
POINT AND OVER COOL (25 DEG CELSIUS) WATERS WHICH ARE NON-CONDUCIVE TO 
SIGNIFICANT TROPICAL DEVELOPMENT, LEADING TO A STEADY WEAKENING TREND. 
BY TAU 36 THE SYSTEM WILL BE AT OR VERY NEAR LANDFALL AS A MINIMAL 
TYPHOON ALONG THE NORTH-CENTRAL COAST OF VIETNAM. AS THE SYSTEM TRACKS 
OVER THE RUGGED TERRAIN OF NORTHERN VIETNAM AND INTO LAOS IT WILL 
BEGIN TO RAPIDLY DECAY DUE TO INCREASING VWS AND TERRAIN INTERACTION 
AND DISSIPATE BY TAU 72 OVER LAOS. NUMERICAL MODEL TRACK GUIDANCE HAS 
COME INTO BETTER AGREEMENT SINCE THE PREVIOUS RUN, WITH 145NM SPREAD 
AT LANDFALL AND ALL BUT NAVGEM AND UKMET ENSEMBLE BEING VERY TIGHTLY 
PACKED NEAR THE MULTI-MODEL CONSENSUS. THE JTWC FORECAST LIES JUST 
NORTH AND SLIGHTLY SLOWER THAN THE CONSENSUS TRACKER WITH HIGH 
CONFIDENCE.//
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