WDPN32 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (VAMCO) WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 25W (VAMCO), LOCATED APPROXIMATELY 528 NM EAST OF DA 
NANG, VIETNAM, HAS TRACKED WESTWARD AT 11 KNOTS OVER THE PAST SIX 
HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS LITTLE 
CHANGE IN THE OVERALL STRUCTURE OF THE SYSTEM, WITH THE LARGE, 
RAGGED EYE THAT WAS EVIDENT SIX HOURS AGO, HAVING NOW FILLED, THOUGH 
A FLARE OF DEEP CONVECTION HAS FORMED OVER THE PAST HOUR OR SO, AND 
IS ATTEMPTING TO WRAP UP THE EASTERN SIDE OF THE CIRCULATION. THE 
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON AN 
EXTRAPOLATION OF A WELL DEFINED MICROWAVE EYE FEATURE EVIDENT IN A 
121018Z SSMIS 36GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS HELD 
STEADY AT 75 KNOTS WITH FAIR CONFIDENCE BASED ON MULTI-AGENCY DVORAK 
CURRENT INTENSITY ESTIMATES BETWEEN T4.0 (65 KNOTS) AND T4.5 (77 
KNOTS). THE ADVANCED DVORAK TECHNIQUE (ADT) ESTIMATE REMAINS T5.2, 
WHICH BASED ON THE OVERALL STRUCTURE OF THE SYSTEM, IS ASSESSED AS 
UNREALISTICALLY HIGH. ENVIRONMENTAL ANALYSIS REVEALS A MARGINAL 
ENVIRONMENT, WITH LOW TO MODERATE (10-15 KNOTS) VWS, AND MODERATE 
EQUATORWARD AND WESTWARD OUTFLOW, THE PREVIOUS POLEWARD OUTFLOW 
CHANNEL HAVING BEEN CONSTRICTED OVER THE PREVIOUS SIX HOURS. SSTS 
REMAIN WARM AT 27-28 DEG CELSIUS). THE SYSTEM CONTINUES TRACKING 
WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) 
TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TY 25W IS FORECAST TO TRACK WESTWARD THROUGH TAU 24 UNDER THE 
STEERING INFLUENCE OF THE STR POSITIONED TO THE NORTH, BEFORE 
ASSUMING A MORE NORTHWESTWARD TRACK THROUGH TAU 72 AS IT TRACKS 
TOWARDS A WEAKNESS WHICH DEVELOPS IN THE STR. TY 25W IS EXPECTED TO 
MAKE LANDFALL NORTH OF HUE AROUND TAU 60. NOW THAT THE POLEWARD 
OUTFLOW CHANNEL HAS BEEN CUT OFF AND OUTFLOW IS CONSTRICTED TO A 
SINGLE CHANNEL, AND THE SYSTEM TRANSITS OVER STEADILY COOLING SSTS, 
THESE FACTORS WILL OFFSET THE LOW VWS AND RESULT IN NO SIGNIFICANT 
CHANGE IN THE INTENSITY THROUGH TAU 24. SHORT EXCURSIONS ABOVE AND 
BELOW 75 KNOTS CAN BE EXPECTED, BUT OVERALL THE INTENSITY WILL 
REMAIN CONSTANT. AFTER TAU 24, SSTS BELOW 26 DEG CELSIUS, HIGHER VWS 
AND UPPER-LEVEL MASS CONVERGENCE WILL COMBINE TO INITIATE A STEADY 
WEAKENING TREND THROUGH LANDFALL.  AFTER LANDFALL, TERRAIN 
INTERACTION OVER CENTRAL VIETNAM AND LAOS WILL QUICKLY WEAKEN THE 
SYSTEM. NUMERICAL MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT 
SINCE THE PREVIOUS RUN, WITH CROSS-TRACK SPREAD NOW 185NM AT TAU 72. 
THE JTWC FORECAST TRACK LIES JUST NORTH OF THE MULTI-MODEL CONSENSUS 
WITH HIGH CONFIDENCE.
   C. AFTER TAU 72, THE SYSTEM WILL RAPIDLY DISSIPATE AS IT TRACKS 
NORTHWESTWARD OVER THE MOUNTAINOUS TERRAIN OF VIETNAM AND LAOS, 
DISSIPATING OVER NORTHERN LAOS BY TAU 96. NUMERICAL MODEL GUIDANCE 
IS IN POOR AGREEMENT IN THE EXTENDED FORECASTS, AS THE VARIOUS MODEL 
TRACKERS LOSING THE VORTEX OVER LAND LEADING TO A 500NM SPREAD AT 
96, LENDING LOW CONFIDENCE IN THE EXTENDED JTWC FORECAST, WHICH LIES 
JUST NORTH OF THE MULTI-MODEL CONSENSUS.//
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