Tropical Storm CHAN-HOM Advisory mié, 07-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 456 NM
EAST OF KADENA AB, OKINAWA, HAS TRACKED WEST-NORTHWESTWARD AT 07
KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) REVEALS CONVECTIVE BANDING WRAPPING INTO THE
LOW LEVEL CIRCULATION CENTER (LLCC), OBSCURED BY FLARING CONVECTION
OVERHEAD. THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION, BASED ON
AN EXTRAPOLATION OF A 062123Z SSMIS 37 GHZ MICROWAVE IMAGE DEPICTING
A WELL-DEFINED MICROWAVE EYE FEATURE AND PLACED NEAR THE PGTW AND
RJTD FIXES. THE INITIAL INTENSITY IS SET AT 60 KTS, HEDGED SLIGHTLY
ABOVE MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T3.5 (55
KTS) AND JUST UNDER A 062052Z SMAP WIND SPEED IMAGE DEPICTING 57 KTS
(10-MINUTE AVERAGE)/63 KTS (1-MINUTE AVERAGE) WINDS. CURRENT 34-KT
AND 50-KT WIND RADII HAVE BEEN UPDATED WITH RECENT ASCAT DATA.
ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE AS TS 16W IS POSITIONED
UNDER AN UPPER LEVEL POINT SOURCE CONTRIBUTING TO ENHANCED POLEWARD
OUTFLOW AND GOOD EQUATORWARD OUTFLOW. ADDITIONALLY, LOW (5-10 KT)
VERTICAL WIND SHEAR (VWS) AND WARM (29-30 CELSIUS) SEA SURFACE
TEMPERATURES (SST) ARE CONDUCIVE FOR CONTINUED DEVELOPMENT. TS 16W
IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE
(STR) POSITIONED TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 16W IS FORECAST TO TRACK GENERALLY NORTHWESTWARD ALONG THE
SOUTHWESTERN PERIPHERY OF THE STEERING STR THROUGH TAU 48,
INTENSIFYING TO A PEAK OF 80 KTS BY TAU 36. TS 16W IS EXPECTED TO
SLOW SIGNIFICANTLY AS IT APPROACHES THE RYUKYU ISLANDS AND BEGINS TO
RECURVE AROUND THE STEERING STR. THE SPREAD IN THE NUMERICAL MODEL
GUIDANCE NEAR THE RECURVE POINT REACHES 192 NM NEAR TAU 48 DUE TO
THE PRESENCE OF A LARGE BREAK IN THE WESTERN AND EASTERN SUBTROPICAL
RIDGES, ALONG WITH THE LACK OF A DYNAMIC MIDLATITUDE SHORTWAVE
TROUGH, WHICH WOULD TYPICALLY ACCELERATE THE SYSTEM POLEWARD. AFTER
TAU 48, THE SYSTEM WILL BEGIN TO CREST THE STR AXIS AND TURN TO A
GENERALLY NORTH-NORTHEASTWARD TRACK THROUGH TAU 72. THE GLOBAL
MODELS CURRENTLY DEPICT A ZONAL PATTERN WITH A SHORTWAVE RIDGE
PROPAGATING OVER THE KOREAN PENINSULA NEAR TAU 60. AS THE SYSTEM
TURNS TO THE NORTH-NORTHEASTWARD TRACK, IT WILL INTERACT WITH THIS
ZONAL FLOW. BASED ON THE COMPLEX STEERING PATTERN AND MODERATE
SPREAD IN SOLUTIONS, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE
JTWC FORECAST TRACK.
   C. IN THE EXTENDED RANGE, TS 16W WILL TRACK NORTHEASTWARD ALONG
THE SOUTHERN COAST OF JAPAN. DUE TO HIGH (>30 KTS) VWS ONSET
BEGINNING AT TAU 72, TS 16W IS EXPECTED TO GRADUALLY WEAKEN FOR THE
REMAINDER OF THE FORECAST PERIOD TO AN INTENSITY OF 50 KTS BY TAU
120. DURING THIS TIME, TS 16W WILL BEGIN TO INTERACT WITH THE
BAROCLINIC ZONE AND COMMENCE EXTRATROPICAL TRANSITION (ETT) BY TAU
72. ETT COMPLETION IS EXPECTED BY TAU 120 AS THE SYSTEM GAINS
FRONTAL CHARACTERISTICS AND BECOMES EMBEDDED IN THE WESTERLY FLOW.
IN THE EXTENDED RANGE, THERE ARE LARGE VARIATIONS IN THE TRACK
SPEEDS WITH GFS, GALWEM, AND GFS ENSEMBLE DISPLAYING SIGNIFICANTLY
FASTER TRACK SPEEDS WHILE THE REMAINDER OF THE GUIDANCE INDICATES
SLOWER TRACK SPEEDS. THE JTWC FORECAST TRACK HAS REMAINED FAIRLY
CONSISTENT AND IS POSITIONED NEAR THE ECMWF AND ECMWF ENSEMBLE MEAN
SOLUTIONS, IN LINE WITH THE MAJORITY OF THE MODEL SOLUTIONS. THE
LATEST MODEL RUN REVEALED NAVGEM AS A SIGNIFICANT OUTLIER TO THE
EAST THAT RECURVES SIGNIFICANTLY FASTER THAN THE MAJORITY OF THE
MODEL SOLUTIONS. DUE TO THESE MODEL DIFFERENCES, THERE IS OVERALL
LOW CONFIDENCE (HIGH UNCERTAINTY) IN THE JTWC FORECAST TRACK.//
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