Tropical Storm VONGFONG Advisory pon., 11.05.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (ONE) WARNING
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 01W (ONE), LOCATED APPROXIMATELY 547
NM EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTH-NORTHWESTWARD AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY SHOWS FLARING CONVECTION OFFSET SOUTHEAST OF THE LOW LEVEL CIRCULATION (LLC), WITH SOME WEAKER FLARING CONVECTION NEAR THE ASSESSED CENTER POSITION. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON EXTRAPOLATION OF A PARTIAL 1237Z ASCAT-B PASS AND ACCOMPANYING AMSU 89 GHZ MICROWAVE IMAGE, AND ANALYSIS OF EXPOSED LOW LEVEL CLOUD BANDS WHICH CAN BE SEEN WRAPPING INTO THE OBSCURED CENTER. THE INITIAL INTENSITY OF 25KTS IS BASED ON THE DVORAK ESTIMATE OF T1.5 (25-30KTS) FROM BOTH PGTW AND RJTD, AND IS SUPPORTED BY A SHIP OBSERVATION OF 28 KNOTS FROM A VESSEL LOCATED APPROXIMATELY 50NM SOUTHEAST OF THE CURRENT POSITION. ANALYSIS
INDICATES TD 01W LIES IN A FAVORABLE ENVIRONMENT WITH LOW (10-15KT)
RELATIVE VWS, MODERATE RADIAL OUTFLOW PROVIDED BY A WEAK POINT SOURCE ALOFT OVER THE SYSTEM AND WARM (28-29C) SEA SURFACE TEMPERATURES (SSTS) AND HIGH OCEAN HEAT CONTENT (OHC) IN THE SOUTHERN PHILIPPINE SEA. THE CYCLONE IS TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) CENTERED OVER THE NORTHERN MARIANAS ISLANDS WITH A NORTH-SOUTH ORIENTED AXIS ALONG ROUGHLY 145E LONGITUDE.
3. FORECAST REASONING.
   A.  THIS IS THE INITIAL PROGNOSTIC REASONING MESSAGE AND SETS THE
FORECAST PHILOSOPHY.
   B. TD 01W WILL TRACK SLOWLY NORTH-NORTHWESTWARD TRAJECTORY OVER THE NEXT 24 HOURS AS THE DEEP-LAYER STR REMAINS ENTRENCHED FAR TO THE EAST. HOWEVER, BY TAU 36 THE STR BEGINS TO REORIENT ONTO A GENERALLY EAST-WEST ORIENTATION AND MOVES TO NEAR 130E LONGITUDE, PUSHING TD 01W ONTO A WEST-NORTHWESTWARD TRACK TOWARDS THE CENTRAL PHILIPPINES. THE SYSTEM IS EXPECTED TO SKIRT THE NORTH SHORE OF SAMAR ISLAND BEFORE MAKING LANDFALL ON THE SOUTHEASTERN PORTION OF LUZON AROUND TAU 72. THE FAVORABLE ENVIRONMENT IS FORECAST TO CONTINUE THROUGH TAU 72 WITH THE POINT SOURCE REMAINING OVERHEAD PROVIDING STRONG RADIAL OUTFLOW ALOFT AND LOW VWS, FUELING STEADY INTENSIFICATION THROUGH TAU 72. THE SYSTEM IS EXPECTED TO REACH PEAK INTENSITY OF 70 KNOTS JUST PRIOR TO LANDFALL.
   C. AFTER TAU 72, TD 01W WILL TRACK NORTHWEST AND THEN NORTHWARD ALONG THE WESTERN PERIPHERY OF THE STR AS IT GRADUALLY MOVES SOUTHEAST, DRAG ACROSS THE LENGTH OF LUZON ISLAND AND THEN REEMERGE OVER WATER IN THE BABUYUAN CHANNEL BY TAU 120. THE SYSTEM WILL STEADILY WEAKEN AS IT TRANSITS OVER THE ROUGH TERRAIN OF LUZON. HOWEVER IT IS EXPECTED THAT THE MAINTENANCE OF ROBUST UPPER-LEVEL POLEWARD OUTFLOW INTO THE MID-LATITUDE WESTERLIES AFTER TAU 96 WILL SERVE TO OFFSET MORE DRASTIC WEAKENING AND THE SYSTEM IS FORECAST TO REEMERGE OVER WATER AS A WEAK TROPICAL STORM. NUMERICAL MODELS ALL CONCUR ON THE GENERAL STAIR STEP TRACK SCENARIO, THEY DIFFER SIGNIFICANTLY IN THE EXACT TRACK, WITH CROSS-TRACK UNCERTAINTY AT TAU 72 EXCEEDING 250NM. BEYOND TAU 72 CROSS AND ALONG-TRACK UNCERTAINTY INCREASE TO MORE THAN 300NM BETWEEN OUTLIERS. THE JTWC FORECAST LIES JUST WEST OF THE MULTI-MODEL CONSENSUS THROUGH TAU 24, WHILE IT LIES NORTH AND EAST, AND SLIGHTLY FASTER THAN THE CONSENSUS THROUGH THE REMAINDER OF THE FORECAST PERIOD IN LIGHT OF THE ECMWF SOLUTION. WITH THE LARGE UNCERTAINTY EVIDENT IN THE NUMERICAL GUIDANCE, THERE IS OVERALL LOW CONFIDENCE IN THE JTWC TRACK FORECAST.//
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