Tropical Storm VONGFONG Advisory Sat May 16

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (VONGFONG) WARNING
NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 01W (VONGFONG), LOCATED APPROXIMATELY 126 NM
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 12
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY (EIR) SHOWS THE CONVECTION IS BECOMING MORE DISORGANIZED
WHILE WRAPPING TIGHTLY INTO THE LOW LEVEL CIRCULATION CENTER (LLCC).
THE INITIAL INTENSITY IS ASSESED AT 60 KNOTS, IN LINE WITH A DVORAK
INTENSITY ESTIMATE OF RJTD T3.5 (60 KNOTS) AND AN ADVANCED DVORAK
INTENSITY ESTIMATE OF T3.8 (61 KTS). THE INITIAL POSITION IS BASED
WITH HIGH CONFIDENCE ON A MICROWAVE EYE SEEN IN A 150527Z AMSR2
89GHZ PASS. ENVIRONMENTAL PARAMETERS REMAIN FAVORABLE WITH RADIAL
OUTFLOW, NEARBY WARM SSTS AND LOW (10-15 KT) VERTICAL WIND SHEAR
(VWS). TS 01W IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A
SUBTROPICAL RIDGE (STR) 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. TS 01W IS FORECAST TO TRACK NORTHWESTWARD ALONG THE
SOUTHWESTERN PERIPHERY OF THE STEERING STR THROUGH TAU 12. AN UPPER-
LEVEL TROUGH TO THE NORTH WILL PASS BETWEEN TAU 12-24, ERODING THE
STR AND FORCING IT TO RECEDE EASTWARD. THIS WILL CLEAR THE WAY FOR
TS 01W TO TURN MORE NORTHWARD AS IT ROUNDS THE STR AXIS BETWEEN TAU
24-36. WITH THE EXCEPTION OF JGSM, NUMERICAL MODEL GUIDANCE IS IN
GOOD AGREEMENT WITH A CROSS TRACK SPREAD OF 135NM AT TAU 48.
HOWEVER, THERE IS SIGNIFICANT PROPAGATION SPEED DIFFERENCES BETWEEN
MODEL SOLUTIONS AS TS 01 BEGINS TO RECURVE. TS 01W IS EXPECTED TO
WEAKEN SIGNIFICANTLY AS IT TRACKS OVER LAND DESPITE ITS FAVORABLE
UPPER LEVEL ENVIRONMENT. TS 01W WILL EMERGE OVER 28-30 DEGREE
CELSIUS SEA SURFACE TEMPERATURE WATER BY TAU 36. HOWEVER, STRONG VWS
WILL HAMPER FURTHER INTENSIFICATION. AFTER TAU 48, TS 01W WILL BEGIN
TO ACCELERATE NORTHEASTWARD.
   C. AFTER TAU 72, HIGH VWS WILL PERSIST AS TS 01W COMES FULLY
UNDER THE UPPER-LEVEL WESTERLIES AND WILL LEAD TO FURTHER WEAKENING.
TS 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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