Tropical Storm VONGFONG Advisory Wed May 13

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (ONE) WARNING
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 01W (ONE), LOCATED APPROXIMATELY 521
NM EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWARD AT
05 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS PERSISTENT, DEEP CONVECTION OBSCURING A LOW
LEVEL CIRCULATION CENTER (LLCC) SLIGHTLY OFFSET TO THE NORTHEAST OF
THE SEMICIRCLE. CONVECTION HAS INCREASED OVER THE PAST 6 HOURS WITH
OVERSHOOTING TOPS DEVELOPING IN THE CONSOLIDATING CONVECTIVE
ENVELOPE. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED
ON PARTIALLY EXPOSED LOW LEVEL BANDS WRAPPING INTO THE OBSCURED LLCC
IN THE MSI LOOP, AS WELL AS EXTRAPOLATION FROM A LOW LEVEL
CIRCULATION APPARENT IN 112330Z ASCAT-A DATA TO THE CENTER OF LOW
LEVEL FEATURES IN A 120456Z AMSR2 89GHZ IMAGE. THE INITIAL INTENSITY
OF 30 KNOTS IS ASSESSED WITH FAIR CONFIDENCE BASED ON DVORAK CURRENT
INTENSITY ESTIMATES OF T2.0 (PGTW 30 KTS) AND T1.5 (RJTD 30 KTS) AND
IS IN LINE WITH THE PERSISTENT CONVECTION PRESENT IN MSI. TD 01W
LIES IN AN ENVIRONMENT FAVORABLE FOR FURTHER INTENSIFICATION WITH
LOW (5-10 KTS) VWS, GOOD EQUATORWARD AND MODEST POLEWARD OUTFLOW AND
WARM (28-29C) SEA SURFACE TEMPERATURES (SSTS). THE SYSTEM IS
TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL
RIDGE (STR) CENTERED OVER THE NORTHERN MARIANA ISLANDS THAT
CONTINUES TO BUILD WESTWARD.
3. FORECAST REASONING.
   A.  THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY
FROM THE LAST PROGNOSTIC REASONING MESSAGE.
   B. OVER THE NEXT 12 HOURS TD 01W WILL TRACK GENERALLY NORTH-NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF A DEEP
NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED STR
CENTERED NORTH OF GUAM. THIS STR IS CURRENTLY BUILDING FARTHER
WESTWARD TOWARDS NORTHERN LUZON AND WILL RESULT IN SUBSEQUENT
STEERING OF TD 01W IN A GENERAL WESTWARD DIRECTION FROM TAU 24 UNTIL
LANDFALL NEAR SAMAR ISLAND AT TAU 48. THE ENVIRONMENT OVER THE NEXT
48 HOURS IS EXPECTED TO REMAIN FAVORABLE FOR FURTHER DEVELOPMENT AS
THE SYSTEM TRAVELS OVER WATER. AN UPPER LEVEL POINT SOURCE SITUATED
ABOVE THE LLCC WILL CONTINUE TO PROVIDE STRONG OUTFLOW, WHILE SEA
SURFACE TEMPERATURES ARE TO REMAIN HIGH (28-29C) AND VWS IS TO
REMAIN LOW (5-10 KTS) ALLOWING FOR FURTHER INTENSIFICATION. THE PEAK I
INTENSITY OF 70 KTS IS FORECAST TO OCCUR AT TAU 48 WHEREUPON THE S
SYSTEM WILL STRUGGLE TO FURTHER INTENSIFY AS IT MAKES LANDFALL AT S
SAMAR ISLAND DUE TO THE FRICTIONAL EFFECTS OF LAND. AFTER REACHING L
LANDFALL AT TAU 48, TD 01W IS FORECAST TO BEGIN TRACKING
WEST-NORTHWESTWARD THROUGH TAU 72. NUMERICAL MODEL SOLUTIONS HAVE C
COME INTO IMPROVING AGREEMENT THROUGH TAU 72 (128 NM SPREAD AT TAU 4
48, 145NM SPREAD AT TAU 72) LENDING FAIR CONFIDENCE TO THIS PORTION O
OF THE JTWC FORECAST TRACK.
   C. AFTER TAU 72 TD 01W WILL BEGIN A NORTHWESTWARD TRACK UNTIL TAU
96 AS IT TRAVELS INLAND. THE FRICTIONAL EFFECTS OF LAND INTERACTION
WILL HINDER FURTHER DEVELOPMENT AND LEAD TO SLIGTH WEAKENING OF THE
SYSTEM, HOWEVER THIS WEAKENING WILL BE OFFSET BY CONTINUED ROBUST
POLEWARD OUTFLOW AND LOW VWS (5-10 KTS). OUTFLOW FROM A TROPICAL
UPPER-TROPOSPHERIC TROUGH (TUTT) CELL POSITIONED OVER THE SOUTH
CHINA SEA WILL IMPINGE UPON THE OUTFLOW OF THE SYSTEM AS IT MOVES
INLAND HOWEVER THIS CELL IS FORECAST TO TRAVEL SOUTHWARD AND CEASE
INTERACTION WITH TD 01W BY TAU 72, AT WHICH POINT IT WILL HAVE
WEAKENED TO 65 KTS. BY TAU 96, THE SYSTEM WILL WEAKEN TO 50 KTS AS
IT BEGINS TO ROUND THE AXIS OF THE STR POSITIONED TO THE EAST AND
TRACK NORTH-NORTHEASTWARD. IT WILL RETAIN ITS INTENSITY OF 50 KTS
DURING THIS TIME DUE TO PERSISTENTLY LOW (5-10 KTS) VWS AND ROBUST
POLEWARD OUTFLOW. TD 01W WILL CONTINUE TO TRACK NORTH-NORTHEASTWARD
AFTER THIS TIME AND REACH THE WARM WATERS OF THE PHILIPPINE SEA
NORTH OF APARRI BY TAU 120. THE SPREAD IN MODEL SOLUTIONS INCREASES
TO 145 NM BY TAU 72 AND THEN SIGNIFICANTLY INCREASES TO 270 NM BY
TAU 96. THE UNCERTAINTY IN MODEL SOLUTIONS IS DUE TO THE TIMING OF
THE BUILDING AND REORIENTATION OF THE STEERING RIDGE WITH EACH OF
THE GLOBAL MODELS PROVIDING A DIFFERENT CENTER POSITION OF THE RIDGE
AT TAU 96-120. THIS INCREASING SPREAD IN MODEL SOLUTIONS AFTER TAU
72 LENDS OVERALL LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST
TRACK.//
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