Tropical Storm VONGFONG Advisory 5月15日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 01W (VONGFONG) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 01W (VONGFONG), LOCATED APPROXIMATELY 197 NM
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 10
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS WEAKENING CONVECTION THAT IS STILL TIGHTLY TURNING
INTO THE CENTER. TY 01W IS CURRENTLY LOCATED OVER MASBATE ISLAND,
PHILIPPINES. THE INITIAL INTENSITY IS SET AT 65 KNOTS, IN LINE WITH
MULTI-AGENCY ESTIMATES AND AN ADVANCED DVORAK TECHNIQUE ESTIMATE OF
T4.0 (65 KTS). THE DRAMATIC WEAKENING IS SUPPORTED BY THE RAGGED
CONVECTIVE STRUCTURE AND OBSERVATIONS FROM ONLY 15 NM AWAY OF A
MINIMUM LOW PRESSURE OF 996 MB FOR THIS COMPACT SYSTEM. THE INITIAL
POSITION WAS BASED WITH FAIR CONFIDENCE ON TIGHT TURNING IN THE EIR
LOOP AND A 1659Z AMSR-2 MICROWAVE IMAGE SHOWING A MICROWAVE EYE
FEATURE. DESPITE ITS POSITION OVER LAND, THE REMAINING ENVIRONMENTAL
PARAMETERS REMAIN FAVORABLE WITH ROBUST RADIAL OUTFLOW, NEARBY WARM
SSTS AND LOW VERTICAL WIND SHEAR (10-15 KNOTS). TY 01W IS BEING
STEERED MOSTLY WESTWARD BY A DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED NORTHEAST OF LUZON WITH AN EXTENSION PAST THE LUZON
STRAIT.
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. THE PREDICTED NORTHWESTWARD TURN IN THE LAST SEVERAL FORECASTS
HAS NOT YET BEEN REALIZED DUE TO THE STR REMAINING ENTRENCHED TO THE
NORTH, LIKELY ENHANCED BY AN UPPER-LEVEL TUTT CELL TO THE SOUTHWEST
IN THE SOUTH CHINA SEA. TY 01W IS FORECAST TO TRACK WEST-
NORTHWESTWARD TO NORTHWESTWARD ALONG THE SOUTHEASTERN PERIPHERY OF
THE STEERING STR. 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. THE JTWC
FORECAST TRACK IS HEDGED WEST OF THE MULTI-MODEL CONSENSUS, TOWARDS
THE ECMWF SOLUTION. BOTH THE ECMWF DETERMINISTIC MEAN AND ITS
ENSEMBLE MEMBERS TRACK THE SYSTEM FURTHER WESTWARD THAN OTHER
MODELS, SKIRTING THE EASTERN EDGE OF THE SOUTH CHINA SEA. AFTER TAU
48, TY 01W SHOULD COMPLETE ROUNDING THE STR AXIS AS IT EMERGES OVER
WATER. THE NEWEST FORECAST TRACK TAKES TY 01W FURTHER WEST OVER THE
STEEP TOPOGRAPHY OF LUZON. TY 01W IS EXPECTED TO WEAKEN
SIGNIFICANTLY AS IT TRACKS OVER LAND DESPITE ITS FAVORABLE UPPER
LEVEL ENVIRONMENT. HOWEVER, SMALL CHANGES IN ITS POSITION WITH
RESPECT TO THE COASTLINE ON EITHER SIDE OF LUZON COULD OFFSET THE
WEAKENING SOMEWHAT. CROSS TRACK SPREAD IS 85 NM AT TAU 48. HOWEVER,
GIVEN THE PROPENSITY OF RECENT MODEL RUNS TO CURVE TY 01W TOO
DRASTICALLY NORTHWARD INTO THE STR, CONFIDENCE IS LOW IN THE JTWC
FORECAST TRACK.
   C. AFTER TAU 72, TY 01W WILL BEGIN ACCELERATING NORTHEASTWARD.
SLIGHT INTENSIFICATION IS POSSIBLE AFTER TY 01W TRACKS BACK OVER 28-
30 DEGREE CELSIUS SEA SURFACE TEMPERATURES TO THE NORTH OF LUZON,
WHERE ITS OUTFLOW WILL ALSO BE ENHANCED BY THE MIDLATITUDE
WESTERLIES TO THE NORTH. HOWEVER, INCREASING VWS (25-30 KNOTS) AS TY
01W NEARS THE BAROCLINIC ZONE, ALONG WITH COOLING SSTS AND
CONVERGENCE ALOFT WHEN IT COMES UNDER STRONG MIDLATITUDE
NORTHWESTERLIES WILL LEAD TO FURTHER WEAKENING OF THE SYSTEM TO 30
KTS BY TAU 96. TY 01W WILL BEGIN EXTRATROPICAL TRANSITION BY TAU 72
AS IT BEGINS TO INTERACT WITH THE BAROCLINIC ZONE, COMPLETING
EXTRATROPICAL TRANSITION BY TAU 96. 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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