Tropical Storm VONGFONG Advisory pt., 15.05.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 01W (VONGFONG) WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 01W (VONGFONG), LOCATED APPROXIMATELY 126 NM
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 12
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS WELL-ORGANIZED FLARING CENTRAL CONVECTION THAT
IS WRAPPING TIGHTLY INTO A CENTER. THE INITIAL INTENSITY IS
MAINTAINED AT 65 KNOTS, IN LINE WITH RJTD AND PGTW DVORAK DATA-T
ESTIMATES OF T4.0 (65 KTS). THE CONVECTION IMPROVED SLIGHTLY AND
FLARED AS TY 01W TRACKED OVER WATER OR SKIRTED THE COAST OF BURIAS
ISLAND OVER THE PAST 6 HOURS. THE INITIAL POSITION IS BASED WITH HIGH
CONFIDENCE ON RADAR DATA FROM THE PHILIPPINES, WHICH STILL SHOWS A
LOW-LEVEL EYE ALTHOUGH IT IS NOT APPARENT IN OVERHEAD SATELLITE
IMAGERY. ENVIRONMENTAL PARAMETERS REMAIN FAVORABLE WITH RADIAL
OUTFLOW THAT IS PARTICULARLY ENHANCED TO THE NORTH, NEARBY WARM SSTS
AND LOW (10-15 KT) VERTICAL WIND SHEAR (VWS). TY 01W HAS TURNED
NORTHWESTWARD IN THE PAST 6 HOURS, TRACKING ALONG THE SOUTHWESTERN
PERIPHERY OF A SUBTROPICAL RIDGE TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE FORECAST
PHILOSOPHY. HOWEVER, SMALL TRACK CHANGES THAT BRING THE SYSTEM MORE
OR LESS OVER WATER OR THE SIGNIFICANT MOUNTAINS OF LUZON MAY HAVE
LARGE IMPACTS ON INTENSITY.
   B. TY 01W IS FORECAST TO TRACK NORTHWESTWARD ALONG THE
SOUTHWESTERN PERIPHERY OF THE STEERING STR THROUGH TAU 36. AN UPPER-
LEVEL TROUGH TO THE NORTH WILL PASS TO THE NORTH BETWEEN TAU 24-36,
ERODING THE STR AND FORCING IT TO RECEDE EASTWARD. THIS WILL CLEAR
THE WAY FOR TY 01W TO TURN MORE NORTHWARD AS IT ROUNDS THE STR AXIS
BETWEEN TAU 36-48. NUMERICAL MODEL GUIDANCE HAS COME INTO BETTER
CROSS TRACK AGREEMENT, WITH THE MAIN GROUPING GOING OVER THE ISLAND
OF LUZON. HOWEVER, THERE IS 70 NM OF ALONG-TRACK SPREAD BETWEEN
MODELS AT TAU 24, INDICATING SIGNIFICANT PROPAGATION SPEED
DIFFERENCES BETWEEN MODEL SOLUTIONS. TY 01W IS EXPECTED TO WEAKEN
SIGNIFICANTLY AS IT TRACKS OVER LAND DESPITE ITS FAVORABLE UPPER
LEVEL ENVIRONMENT. TY 01W WILL EMERGE OVER 28-30 DEGREE CELSIUS SEA
SURFACE TEMPERATURE WATER BY TAU 36. HOWEVER, VWS WILL BEGIN
INCREASING AT THAT POINT, AND SYSTEM ORGANIZATION WILL HAVE BEEN
DISRUPTED BY THE ROUGH TERRAIN OF LUZON. MODEL INTENSITY GUIDANCE FOR
THE PERIOD AFTER TY 01W EMERGES OVER WATER LOWERED ITS EXPECTATIONS
THIS RUN, AND THE JTWC FORECAST INTENSITY HAS BEEN LOWERED
ACCORDINGLY. AFTER TAU 48, TY 01W WILL BEGIN TO ACCELERATE
NORTHEASTWARD. BETWEEN TAU 48-72, TY 01W MAY MAINTAIN INTENSITY AS IT
PASSES OVER 27-29 DEGREE CELSIUS WATER AND OUTFLOW IS BRIEFLY
ENHANCED AS IT TAPS INTO THE UPPER-LEVEL WESTERLIES TO THE NORTH.
   C. AFTER TAU 72, HIGH VWS AND CONVERGENCE ALOFT AS TY 01W COMES
FULLY UNDER THE UPPER-LEVEL WESTERLIES WILL LEAD TO FURTHER
WEAKENING. TY 01W WILL BEGIN TO INTERACT WITH THE BAROCLINIC ZONE AT
TAU 72, AND COMPLETE EXTRATROPICAL TRANSITION BY TAU 96. IT IS ALSO
POSSIBLE THAT IT DISSIPATES UNDER THE MIDLATITUDE WESTERLIES BEFORE
IT CAN COMPLETE EXTRATROPICAL TRANSITION. THERE IS SIGNIFICANT ALONG
TRACK SPREAD OF MODEL SOLUTIONS AFTER TAU 72. THE LARGE SPREAD IN
MODEL GUIDANCE LENDS LOW CONFIDENCE TO THIS PORTION OF THE JTWC
FORECAST TRACK.//
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