Tropical Storm VONGFONG Advisory Mi, 13.05.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (VONGFONG) WARNING
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 01W (VONGFONG), LOCATED APPROXIMATELY
491 NM EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED
WESTWARD AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED HIGH RESOLUTION
(1-KM) AND HIGH REFRESH RATE (2-MIN) ENHANCED INFRARED (EIR) AND
VISIBLE SATELLITE IMAGERY SHOWS A SMALL AREA OF DEEP CONVECTION WITH
FLARING CONVECTIVE HOT TOWERS ROTATING ABOUT THE ASSESSED CENTER
LOCATION. THESE HOT TOWERS AND OVERSHOOTING TOPS WILL FLARE ABOUT ONCE
PER HOUR, FLIRT WITH FORMING AN EYE AND THEN DISSIPATE. OVER THE PAST
HOUR HOWEVER THE WARM SPOT HAS BEEN ABLE TO MAINTAIN ITSELF A BIT MORE
SO DEVELOPMENT OF A CLOUD FILLED EYE COULD BE IMMINENT. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE DIMPLE IN THE
VISIBLE IMAGERY AND ACCOMPANYING WARM SPOT IN THE INFRARED, SUPPORTED
BY A 2211Z SSMIS 91 GHZ COLORPCT MICROWAVE IMAGE WHICH SHOWED A
DEVELOPING MICROWAVE EYE. SURROUNDED BY DEEP CONVECTION. THE INITIAL
INTENSITY OF 60 KNOTS IS HEDGED UPWARD SLIGHTLY FROM THE PGTW CURRENT
INTENSITY ESTIMATE OF T3.5 (55 KNOTS) IN LIGHT OF THE NASCENT EYE
DEVELOPMENT, AND IS SUPPORTED BY AN ADVANCED DVORAK TECHNIQUE (ADT)
ESTIMATE OF T3.4 (54 KNOTS). EXPECT THAT ONCE THE EYE DOES FORM
INTENSITIES WILL JUMP UP DRAMATICALLY. THE ENVIRONMENT REMAINS VERY
FAVORABLE FOR ADDITIONAL RAPID INTENSIFICATION, WITH LOW (5-10 KTS)
VWS, WARM SSTS AND ROBUST RADIAL OUTFLOW ALOFT. HOWEVER, A WEDGE OF
RELATIVELY DRIER AIR IS BEING ENTRAINED SOUTHWARD ALONG THE WEST SIDE
OF THE SYSTEM, IMPINGING THE OUTFLOW FROM THIS QUADRANT, AND PROVING
TO A LIMITING FACTOR ON EVEN FASTER INTENSIFICATION IN THE NEAR-TERM.
OVER THE PAST SIX HOURS THE SYSTEM TOOK A BIT OF AN UNEXPECTED MOTION,
BECOMING NEARLY QUASI-STATIONARY FOR A SHORT TIME AND THEN MOVING DUE
WEST OR EVEN SLIGHTLY SOUTH OF WEST AS IT CONTINUES TO CONSOLIDATE.
UPPER-LEVEL PATTERN ANALYSIS INDICATES THE STR CENTERED WELL TO THE
EAST NEAR GUAM BUILT IN AND EXTENDED WESTWARD FASTER THAN ANTICIPATED,
PUSHING TS 01W ONTO THE MORE WESTWARD TRACK.
3. FORECAST REASONING.
   A. THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY
SINCE THE PREVIOUS FORECAST BULLETIN.
   B. AS PREVIOUSLY DISCUSSED THE RECENT MOTION HAS BEEN MORE WESTWARD
THAN PREVIOUSLY FORECAST, AND THIS TREND IS EXPECTED TO CONTINUE WITH
TS 01W MOVING VERY CLOSE TO DUE WEST THROUGH TAU 12 ALONG THE
SOUTHWESTERN PERIPHERY OF AN EXTENSION OF THE DEEP-LAYER STR STILL
CENTERED OVER THE NORTHERN MARIANAS. AFTER TAU 12 AND THROUGH TAU 72,
THE STR BECOMES RECENTERED FURTHER WEST NEAR 130E AND TS 01W WILL
GRADUALLY TRACK MORE NORTHWESTWARD AS TIME PROGRESSES. THE STR WILL
MOVE BACK EAST-SOUTHEAST AFTER TAU 48 WITH A RIDGE AXIS LYING NEAR 18N
LATITUDE AND TS 01W WILL BY THIS TIME START TRACKING NORTHWESTWARD
TOWARDS THE RIDGE AXIS. TS VONGFONG IS FORECAST TO CONTINUE TO RAPIDLY
INTENSIFY OVER THE NEXT 24 HOURS AS ENVIRONMENTAL CONDITIONS REMAIN
HIGHLY FAVORABLE WITH WARM WATERS, LOW VWS AND ROBUST RADIAL OUTFLOW.
WHILE THE SYSTEM IS CURRENTLY EXPERIENCING SOME DRY AIR ENTRAINMENT
WHICH IS LIMITING DEVELOPMENT, THE ATMOSPHERE IS FORECAST TO MOISTEN
OVER THE NEXT 6 TO 12 HOURS ALLOWING MORE RAPID INTENSIFICATION TO
OCCUR. AFTER TAU 24 THE INTENSIFICATION TREND IS EXPECTED CONTINUE,
ALBEIT AT A SLOWER RATE, REACHING A PEAK INTENSITY OF 95 KNOTS JUST
PRIOR TO LANDFALL AT CATANDUANES ISLAND NEAR TAU 48, THEN MAINTAIN
INTENSITY AS IT CROSSES BACK INTO OPEN WATERS EAST OF LUZON. THE
SYSTEM IS EXPECTED TO MAKE A SECOND LANDFALL ALONG THE EAST COAST OF
CENTRAL LUZON JUST AFTER TAU 72. DYNAMIC GUIDANCE IS IN FAIRLY GOOD
AGREEMENT THROUGH TAU 48 WITH A SPREAD OF 137 NM, INCREASING TO 195 NM
BY TAU 72. THE MAJORITY OF MODELS (ECMWF, GFS, NAVGEM, JGSM AND THEIR
ENSEMBLES) ARE IN AGREEMENT ON A WEST-NORTHWESTWARD TRACK WHICH STAYS
EITHER OFFSHORE OR JUST BRUSHES THE EAST COAST OF SAMAR AND SOUTHEAST
LUZON. THE REMAINDER OF THE MODELS (GALWEM, UKMET AND THE ENSEMBLE)
TAKE A TRACK FURTHER SOUTH OVER THE CENTRAL PHILIPPINES AND INTO THE
SOUTH CHINA SEA. THE JTWC OFFICIAL TRACK LIES ALONG THE RIGHT SIDE OF
THE TIGHTEST GROUPING OF MODELS MENTIONED EARLIER AND JUST NORTH AND
EAST OF THE MULT-MODEL CONSENSUS TRACK, LENDING HIGH CONFIDENCE IN
THIS PORTION OF THE FORECAST.
   C. BEYOND TAU 72, THE FORECAST BECOMES LESS CERTAIN IN REFERENCE TO
THE EXACT TRACK, THOUGH ALL AVAILABLE GUIDANCE AGREES ON THE GENERAL
RECURVE SCENARIO. AFTER MAKING ITS SECOND LANDFALL IN EAST-CENTRAL
LUZON TS VONGFONG WILL MOVE ACCELERATE NORTHWARD WHILE ROUNDING THE
RIDGE AXIS AND REEMERGE INTO THE LUZON STRAIT BY TAU 96. BY TAU 120
THE SYSTEM WILL BE MOVING RAPIDLY NORTHEASTWARD SOUTHEAST OF THE RYUKU
ISLANDS WHILST UNDERGOING EXTRA-TROPICAL TRANSITION AS IT MOVES UNDER
THE DEEP MID-LATITUDE WESTERLY FLOW. TS 01W IS FORECAST TO RAPIDLY
WEAKEN AFTER MAKIN LANDFALL ON LUZON DUE TO TERRAIN INTERACTION, THEN
CONTINUE TO WEAKEN AFTER MOVING BACK OVER WATER DUE TO RAPIDLY
INCREASING VWS AND COOLER SSTS WHICH WILL COMBINE TO OFFSET THE VERY
ROBUST OUTFLOW. ALL NUMERICAL MODEL GUIDANCE AGREES ON THE TRACK
SCENARIO BEYOND TAU 72, BUT DIFFERS SIGNIFICANTLY ON THE ALONG-TRACK
SPEED, LEADING TO SIGNIFICANT UNCERTAINTY IN THE FORECAST TRACK.
ALONG-TRACK SPREAD INCREASES TO NEARLY 1000 NM BY TAU 120 BETWEEN THE
EGRR AND GFS OUTLIERS. HOWEVER THE MAJORITY OF THE GUIDANCE FALLS INTO
A GPCE ELLIPSE OF ABOUT 650 NM. THE JTWC TRACK LIES VERY NEAR THE
MULTI-MODEL CONSENSUS AND A COUPLE OF KNOTS SLOWER THAN THE CONSENSUS
TRACK SPEED. IN LIGHT OF THE HIGH AMOUNT OF ALONG-TRACK UNCERTAINTY,
THERE IS LOW CONFIDENCE IN THIS PORTION OF THE FORECAST.//
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