Tropical Storm VAMCO Advisory jue, 12-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (VAMCO) WARNING NR
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 25W (VAMCO), LOCATED APPROXIMATELY 110 NM EAST OF
MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 07 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
SHOWS THE SYSTEM CONTINUED TO INTENSIFY AS EVIDENCED BY COOLING
CONVECTIVE TOPS OVER THE EYEWALL SURROUNDING A PINHOLE 10-NM DEFINED
EYE, EVEN AS ITS WESTERN RAIN BANDS ARE NOW SWEEPING ACROSS THE
PHILIPPINE ARCHIPELAGO. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE EYE FEATURE THAT LINED UP WELL WITH A
SHARPLY-OUTLINED CIRCULATION CENTER ON A COMPOSITE RADAR LOOP FROM
PAGASA. THE INITIAL INTENSITY OF 90KTS IS BASED ON THE PGTW DVORAK
ESTIMATE OF T5.0/90KTS AND SATCON ESTIMATE OF 88KTS, AND REFLECTS
THE 6-HR INTENSIFICATION. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM
REMAINS IN A FAVORABLE AREA WITH LOW (05-10KT) VERTICAL WIND SHEAR
(VWS) AND STRONG RADIAL OUTFLOW ASSOCIATED WITH A POINT SOURCE
DIRECTLY OVERHEAD. ADDITIONALLY, SEA SURFACE TEMPERATURES (SST) IN
THE PHILIPPINE SEA REMAIN WARM AND FAVORABLE AT 29-30C. HOWEVER, THE
SYSTEM IS NOW POISED TO MAKE LANDFALL INTO THE RUGGED TERRAIN OF
LUZON. THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A
DEEP-LAYERED 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 WILL CONTINUE ON ITS CURRENT TRACK TOWARD CENTRAL
LUZON, MAKING LANDFALL OVER THE PROVINCE OF BULACAN AROUND TAU 06,
DRAG ACROSS PAMPANGA AND ZAMBALES, BEFORE EXITING INTO THE SOUTH
CHINA SEA (SCS) SHORTLY AFTER TAU 12. AFTERWARD, AS THE STR BUILDS,
IT WILL TRACK MORE WESTWARD. LAND INTERACTION WILL MAINLY WEAKEN IT
TO 65KTS BY TAU 24 AFTER IT EXITS IN THE SCS.  THE WARM WATERS OF
THE SCS (29C) AND FAVORABLE VWS WILL FUEL A GRADUAL INTENSIFICATION
TO A SECONDARY PEAK OF 70KTS AT TAUS 36-48. AFTERWARD, TY 25W WILL
TRACK MORE WEST-NORTHWESTWARD, AS THE STR IS WEAKENED BY AN
APPROACHING MIDLATITUDE TROUGH TO THE NORTH, OVER COOLING SST AND
DECREASING OCEAN HEAT CONTENT (OHC) IN THE WESTERN SCS THAT WILL
WEAKEN IT TO 45KTS BY TAU 72 AS IT APPROACHES VIETNAM. NUMERICAL
MODELS ARE IN TIGHT AGREEMENT, LENDING HIGH CONFIDENCE IN THIS
PORTION OF THE JTWC FORECAST TRACK WHICH IS PLACED NEAR THE MULTI-
MODEL CONSENSUS.
   C. AFTER TAU 72, TY VAMCO WILL CONTINUE ON A WEST-NORTHWESTWARD
TRACK, MAKING LANDFALL OVER CENTRAL VIETNAM, JUST NORTH OF HUE,
AROUND TAU 90. SST DROPS TO 27C AND OHC DOWN TO 25KJ/CM^2 NEAR
VIETNAM. THESE, PLUS THE RUGGED TERRAIN WILL RAPIDLY ERODE THE
SYSTEM TO 25 KTS BY TAU 96 AFTER LANDFALL, THEN TO EVENTUAL
DISSIPATION BY TAU 120 AFTER IT CROSSES INTO CENTRAL LAOS. NUMERICAL
MODELS GRADUALLY AND EVENLY SPREAD TO OVER 500NM BY TAU 120, WITH
AFUM AS THE NOTABLE RIGHT OUTLIER, OFFERING AN UNLIKELY U-TURN TRACK
OVER HAINAN. THERE IS OVERALL FAIR CONFIDENCE IN THE EXTENDED
PORTION OF THE JTWC FORECAST TRACK THAT IS PLACED JUST LEFT OF THE
MULTI-MODEL CONSENSUS TO OFFSET AFUM.//
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