Tropical Storm VAMCO Advisory Fri Nov 13

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (VAMCO) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 25W (VAMCO), LOCATED APPROXIMATELY 354 NM EAST OF DA
NANG, VIETNAM, HAS TRACKED WESTWARD AT 11 KNOTS OVER THE PAST SIX
HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TIGHTLY
CURVED CONVECTIVE BANDS WRAPPING INTO A SMALL, CLOUD-OBSCURED EYE.
THE MSI ALSO REVEALS A LARGE FIELD OF LOW-LEVEL STRATOCUMULUS
EXTENDING ALL THE WAY TO HAINAN. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE WELL DEFINED EYE IN HIGH RESOLUTION
VISIBLE IMAGERY. THE INITIAL INTENSITY REMAINS AT 75 KTS, AND IS
ASSESSED WITH FAIR CONFIDENCE BASED ON ANALYSIS OF MULTI-AGENCY
DVORAK CURRENT INTENSITY ESTIMATES BETWEEN T3.5 (55 KNOTS) AND T4.5
(77 KNOTS), WHILE THE ADVANCED DVORAK TECHNIQUE (ADT) ESTIMATES
REMAIN UNREASONABLY HIGH AT T5.5. TY VAMCO IS TRACKING WESTWARD ALONG
THE SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE
NORTHEAST AND THROUGH A FAVORABLE ENVIRONMENT WITH LOW (5-10 KTS)
VERTICAL WIND SHEAR, WARM (27-28 CELSIUS) SEA SURFACE TEMPERATURES
(SST) AND WELL ESTABLISHED POLEWARD AND EQUATORWARD OUTFLOW ALOFT.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   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. THE ENVIRONMENT IS FORECAST TO
REMAIN GENERALLY FAVORABLE DURING THE FIRST 12 HOURS OF THE FORECAST,
WITH SSTS ABOVE27 DEG CELSIUS, VWS IN THE LOW TO MODERATE RANGE AND
MODERATE UPPER-LEVEL OUTFLOW, SUPPORTING A PERIOD OF STEADY
INTENSITY. AFTER TAU 12 HOWEVER, ENVIRONMENT WILL SLOWLY DEGRADE,
WITH THE PRIMARY FACTOR DRIVING THE WEAKENING TREND BEING THE STEADY
DECREASE IN SSTS AS THE SYSTEM APPROACHES THE COAST OF VIETNAM.
CURRENT SST MEASUREMENTS INDICATE SSTS DECREASE TO LESS THAN 26 DEG
CELSIUS WEST OF THE 110 DEG LONGITUDE, AND AFTER THE SYSTEM CROSSES
THIS POINT AFTER TAU 36, IT WILL QUICKLY WEAKEN THROUGH LANDFALL. THE
SYSTEM IS FORECAST TO MAKE LANDFALL NEAR TAU 48 ALONG THE COAST OF
NORTH-CENTRAL VIETNAM, HAVING WEAKENED TO 45 KNOTS. 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 IS IN FAIR AGREEMENT THROUGH TAU 36 BUT YIELDS POOR GUIDANCE
THEREAFTER AS MODELS DIVERGE. SIGNIFICANTLY, THE UKMET ENSEMBLE
TRACKS THE VORTEX NORTH TOWARDS THE CHINA/VIETNAM BORDER WHILE THE
REMAINDER OF THE MODEL TRACKERS ARE WELL CLUSTERED NEAR THE JTWC
FORECAST TRACK. HOWEVER, DUE TO THE PREPONDERANCE OF THE MODEL
GUIDANCE BEING TIGHTLY PACKED, THERE IS OVERALL HIGH CONFIDENCE IN
THE JTWC FORECAST TRACK WHICH LIES ON THE NORTHERN EDGE OF THE
GUIDANCE ENVELOPE.//
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