Tropical Storm NAMTHEUN Advisory vie, 02-09

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (NAMTHEUN) WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 15W (NAMTHEUN), LOCATED APPROXIMATELY 161 NM EAST OF
KADENA AB, HAS TRACKED NORTH-NORTHEASTWARD AT 06 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS BANDING CONVECTION WRAPPING INTO A SMALL AND COMPACT
SYSTEM WITH AN EYE FEATURE STARTING TO EMERGE. RECENT RADAR
DATA FROM JMA SHOWS THE HIGH RESOLUTION CIRCULATION CENTER LENDING
HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY IS
ASSESSED AT 70 KNOTS AND IS BASED ON IMPROVEMENT IN THE CONVECTIVE
STRUCTURE AND RECENT DVORAK ESTIMATES FROM ALL AGENCIES REPORTING
THE CURRENT INTENSITY RANGING BETWEEN T4.0 TO T4.5 (65 TO 77 KNOTS).
UPPER-LEVEL ANALYSIS SHOWS THE PRESENCE OF A STRONG
POLEWARD OUTFLOW CHANNEL INTO A TROUGH JUST OFF TO THE NORTHWEST AND
COMPETING SOUTHWESTERLY FLOW WHICH IS HINDERING ANY SUBSTANTIAL
EQUATORWARD OUTFLOW. SEA SURFACE TEMPERATURES ARE FAVORABLE, NEAR 30
CELSIUS, WITH HIGH OCEAN HEAT CONTENT. CURRENTLY TY 15W IS TRACKING
NORTHEAST AND DEACCELERATING INTO A WEAK STEERING ENVIRONMENT AS THE
NEAR-EQUATORIAL RIDGE MOVES OFF TO THE SOUTHWEST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE, HOWEVER THE FORECAST TRACK REFLECTS A
FASTER TRACK SPEED WITH A SLIGHTLY SHARPER TURN TO THE NORTHEAST.
   B. IN THE SHORT-TERM FORECAST TY 15W WILL REMAIN IN A SOMEWHAT
WEAK STEERING ENVIRONMENT OVER THE NEXT 36 HOURS AS A DEEP-LAYERED
SUBTROPICAL RIDGE TO THE NORTHEAST SLOWLY BUILDS AND GENTLY GUIDES
TY 15W TO THE NORTH-NORTHWEST. INTENSIFICATION IS EXPECTED OVER THE
NEXT 36 HOURS REACHING A PEAK INTENSITY OF 90 KNOTS.
INTENSIFICATION IS PARTICULARLY DIFFICULT TO GAUGE AS WESTERLY WINDS
ALOFT WILL CONTINUE TO COMPETE WITH THE STRONG POLEWARD CHANNEL INTO
THE TROUGH, AND FAVORABLE WATERS WILL PERSIST. AROUND TAU 36 THE
STEERING RIDGE WILL BUILD SUFFICIENTLY TO STEER TY 15W INTO THE HIGH
WIND SHEAR OF THE UPPER-LEVEL TROUGH AND BEGIN TO WEAKEN
CONSIDERABLY. SHORTLY AFTER TAU 48 LANDFALL IS EXPECTED WITH AN
ACCOMPANIED CHANGE OF TRACK TO THE NORTHEAST.
    C. IN THE EXTENDED TAUS TY 15W WILL CONTINUE NORTHEAST UNDER THE
INFLUENCE OF THE TROUGH FURTHER WEAKENING THE SYSTEM. TY 15W IS
EXPECTED TO START TRANSITIONING INTO AN EXTRATROPICAL SYSTEM AROUND
TAU 96, BECOMING FULLY EXTRATROPICAL BY TAU 120. DYNAMIC MODEL
GUIDANCE IS IMPROVING SOMEWHAT, SHOWING TIGHTER GROUPING IN TRACKS
THROUGH TAU 72 AS IT MAKES LANDFALL AND TURNS NORTHEAST. THE 12Z
ECMFW SOLUTION WAS SHOWING A FASTER TRACK THAN EACH OF THE OTHER 12Z
SOLUTIONS. THE BULK OF THE 18Z SOLUTIONS HAVE SPED UP NEARLY
MATCHING THE INTERPOLATED ECMWF SOLUTION. THE FORECAST TRACK
REFLECTS THE INCREASE IN SPEED AND CONSEQUENTLY A SLIGHTLY TIGHTER
TURN TO THE NORTHEAST. WHILE UNCERTAINTY STILL REMAINS, THERE IS
GOOD CONFIDENCE IN THE FORECAST TRACK.//
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