Tropical Storm VONGFONG Advisory Thu May 14

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (VONGFONG) WARNING
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 01W (VONGFONG), LOCATED APPROXIMATELY 465 NM EAST-
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT
04 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS SYMMETRICAL, SPIRAL BANDS WRAPPING INTO A
CENTER THAT CONTINUES TO BE OBSCURED BY CONVECTION. A DIMPLE IN THE
CENTRAL CONVECTION HAS BEGUN TO FORM, HOWEVER. THIS FEATURE, ALONG
WITH A COOLING TREND OF THE SYSTEM CENTER NOTED IN ANIMATED ENHANCED
INFRARED (EIR) IMAGERY, INDICATES THAT EYE FORMATION IS IMMINENT.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
DIMPLE IN THE VISIBLE IMAGERY AS WELL AN EYE FEATURE NOTED IN THE
EIR LOOP AND IS INLINE WITH FIXES FROM PGTW, RJTD AND RCTP. THE
INITIAL INTENSITY OF 70 KNOTS IS HEDGED ABOVE THE PGTW CURRENT
INTENSITY ESTIMATE OF T4.0 (65 KTS) DUE TO THE IMPENDING EYE
FORMATION AND STRUCTURE OF THE SYSTEM. THE ENVIRONMENT REMAINS VERY
FAVORABLE FOR ADDITIONAL RAPID INTENSIFICATION, WITH LOW (5-10 KTS)
VWS, WARM SSTS (29-30 C) AND ROBUST RADIAL OUTFLOW ALOFT. TY VONGFONG
IS STEERED BY A DEEP-LAYER SUBTROPICAL RIDGE POSITIONED TO THE EAST
NEAR GUAM WHICH IS EXTENDING WEST TOWARD THE LUZON STRAIT.
3. FORECAST REASONING.
   A. THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY
SINCE THE PREVIOUS FORECAST BULLETIN.
   B. TY VONGFONG WILL CONTINUE TO TRACK WEST-NORTHWESTWARD THROUGH
TAU 36 UNDER THE STEERING INFLUENCE OF A BUILDING STR TO THE EAST.
CONDITIONS IN THE AREA WILL REMAIN HIGHLY FAVORABLE FOR RAPID
INTENSIFICATION WITH CONTINUED WARM (29-30 C) SSTS, LOW (5-10 KTS)
VWS AND DIVERGENCE ALOFT. THESE CONDITIONS WILL ALLOW THE SYSTEM TO
INTENSIFY TO 100 KTS BY TAU 36 WHEREUPON IT WILL BEGIN TO CROSS OVER
CATANDUANES ISLAND. A SLIGHT WEAKENING OF THE SYSTEM TO 95 KTS BY
TAU 48 WILL OCCUR DUE TO THE FRICTIONAL EFFECTS OF LAND, HOWEVER
THIS WILL BE OFFSET BY CONTINUED FAVORABLE CONDITIONS AND ROBUST
OUTFLOW. AFTER TAU 48, TY VONGFONG WILL TURN NORTH-NORTHWEST AND
ACCELERATE AS IT BEGINS TO RECURVE AROUND THE STR. BY TAU 72, THE
SYSTEM WILL REACH LANDFALL FOR A SECOND TIME OVER LUZON WHEREUPON IT
WILL WEAKEN TO 85 KTS DUE TO TERRAIN EFFECTS. DYNAMIC MODEL GUIDANCE
IS IN FAIR AGREEMENT THROUGH TAU 48 WITH A SPREAD OF 167 NM. THE
DEVIATION OF MODEL SOLUTIONS IS DUE TO THE DYNAMIC NATURE OF A
REORIENTATION OF THE STEERING STR AND RESULTS IN ONLY FAIR CONFIDENCE
IN THE TIMING AND LOCATION OF THE RECURVATURE. CROSS TRACK SPREAD IN
MODEL SOLUTIONS INCREASE TO 350 NM BY TAU 72. GFS, NAVGEM AND JGSM
MODEL SOLUTIONS ALL BRING THE SYSTEM OVER LUZON BY TAU 72 WHEREAS
ECMWF, AFUM AND UKMET SOLUTIONS PROVIDE A MORE WESTWARD TRACK,
BRINGING TY VONGFONG INTO THE SOUTH CHINA SEA. THE OFFICIAL JTWC
FORECAST TRACK LIES ALONG THE EAST SIDE OF THE TIGHTEST GROUPING OF
MODELS MENTIONED EARLIER (GFS, NAVGEM AND JGSM) AND JUST NORTH AND
EAST OF THE MULT-MODEL CONSENSUS TRACK, LENDING OVERALL FAIR
CONFIDENCE IN THIS PORTION OF THE FORECAST.
   C. AFTER TAU 72, TY VONGFONG WILL ROUND THE STR AXIS AND BEGIN A
GENERALLY NORTH-NORTHEASTWARD TRACK. AS IT TRAVELS OVER LUZON AND
REENTERS THE PHILIPINE SEA IT WILL WEAKEN TO 65 KTS BY TAU 96 DUE TO
THE FRICTIONAL EFFECTS OF LAND AND INCREASING VWS (20-25 KTS),
ALTHOUGH POLEWARD OUTFLOW IS EXPECTED TO REMAIN ROBUST AS IT TAPS
INTO THE DEEP WESTERLY FLOW ALOFT. THIS WEAKENING TREND WILL CONTINUE
AS THE SYSTEM TRAVELS INTO THE LUZON STRAIT, EVENTUALLY WEAKENING TO
50 KTS BY TAU 120, AT WHICH TIME IT WILL BEGIN EXTRATROPICAL
TRANSITION. MODEL SOLUTIONS BEGIN TO DIVERGE FURTHER AFTER TAU 72
WITH A CROSS TRACK SPREAD OF 424 NM BY TAU 96. ADDITIONALLY, THE
ALONG TRACK SPREAD OF MODEL SOLUTIONS INCREASES SIGNIFICANTLY BY TAU
120 WITH A SPREAD OF 898 NM WHEN ALL MEMBERS OF THE MULTI-MODEL
CONSENSUS ARE INCLUDED. THE LARGE SPREAD IN BOTH ALONG AND CROSS
TRACK MODEL GUIDANCE LENDS HIGH UNCERTAINTY DURING THIS PERIOD AND
THUS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.//
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