Tropical Storm VAMCO Advisory vie, 13-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (VAMCO) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 25W (VAMCO), LOCATED APPROXIMATELY 149 NM WEST-
NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 12 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS A WEAKENED SYSTEM WITH A BROAD, RAGGED, ELONGATED EYE
FEATURE WITH SHALLOW CONVECTIVE BANDING WRAPPING INTO THE WELL-
DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE BROAD EYE FEATURE SUPPORTED
BY THE A WELL-DEFINED MICROWAVE EYE FEATURE IN A 120546Z AMSR2 36GHZ
MICROWAVE IMAGE. THE INITIAL INTENSITY IS ASSESSED 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 OF T5.2 IS ASSESSED AS
UNREALISTICALLY HIGH AT THIS TIME. THE SYSTEM IS TRACKING WESTWARD
ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) POSITION
TO THE NORTHEAST, THROUGH A FAVORABLE ENVIRONMENT OF MODERATE RADIAL
OUTFLOW, WITH WEAK POLEWARD OUTFLOW INTO THE WESTERLIES TO THE NORTH,
LOW (5-10 KNOTS) VERTICAL WIND SHEAR (VWS) AND WARM (27-28 DEC
CELSIUS).
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 48 UNDER THE
STEERING INFLUENCE OF THE STR POSITIONED TO THE NORTH. AFTER TAU 48,
THE SYSTEM WILL TRACK MORE WEST-NORTHWESTWARD AND SLOW, AS IT
TRANSITS SOUTH OF A WEAKNESS IN THE STR WHICH DEVELOPS TO THE NORTH
OVER HAINAN. OVER THE NEXT 24 HOURS, AS THE SYSTEM TRACK OVER
RELATIVELY WARM WATERS AND VWS REMAINS LOW, IT IS FORECAST TO
INTENSIFY SLIGHTLY, TO A PEAK OF 80 KNOTS. HOWEVER, AFTER TAU 36,
SSTS WILL QUICKLY COOL TO 26 DEG CELSIUS OR COOLER, AND IN
CONJUNCTION WITH DRY AIR ENTRAINMENT, WILL SUPPORT A GRADUAL
WEAKENING TREND. TY 25W IS EXPECTED TO MAKE LANDFALL NORTH OF HUE,
VIETNAM JUST PRIOR TO TAU 72, THEN TRACK WEST-NORTHWEST WHILE
WEAKENING. NUMERICAL MODEL GUIDANCE DIVERGES STEADILY AFTER TAU 24,
WITH A 305NM SPREAD AT TAU 72. THE GFS AND GFS ENSEMBLE FORM A GROUP
WHICH TRACKS THE SYSTEM NEARLY DUE WEST THROUGH TAU 96, WHILE THE
UKMET ENSEMBLE AND AFUM REPRESENT THE POLEWARD GROUP, TAKING THE
SYSTEM NORTHWARD JUST WEST OF HAINAN BY TAU 72. THE JTWC FORECAST
TRACK LIKES JUST SOUTH OF THE MULTI-MODEL CONSENSUS TRACK 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, WITH SPREAD INCREASING
TO NEARLY 500NM BY TAU 96 BETWEEN THE GFS AND UKMET OUTLIERS, LENDING
LOW CONFIDENCE TO THIS PORTION OF THE FORECAST TRACK.//
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