WDPN31 PGTW 271500
MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 13W (NAMTHEUN)
/WARNING NR 11//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 271200Z2 JUL 2004 TO 011200Z4 AUG 2004.
   A. TYPHOON (TY) 13W (NAMTHEUN), LOCATED APPROXIMATELY 420 NM
SOUTHEAST OF TOKYO, JAPAN, HAS TRACKED NORTHWESTWARD AT 14 KNOTS
OVER THE PAST 06 HOURS. THE WARNING POSITION IS BASED ON 271130Z4
ENHANCED INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED
ON SATELLITE CURRENT INTENSITY ESTIMATES OF 90 AND 102 KNOTS.
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY REVEALS THAT THE EYE
FEATURE IS NO LONGER EVIDENT AND THAT THE DEEP CONVECTION HAS
DECREASED SOMEWHAT IN THE WESTERN SEMICIRCLE OF THE CYCLONE.
   B. TY 13W IS EXPECTED TO CONTINUE TRACKING NORTHWESTWARD FOR THE
NEXT 12 HOURS ALONG THE SOUTHWEST QUADRANT OF THE MID-LEVEL
STEERING RIDGE TO THE NORTHEAST OF THE SYSTEM. AFTER 12 HOURS, THIS
RIDGE WILL BEGIN BUILDING WESTWARD AND STRENGTHENING, CAUSING A
MORE WESTWARD TRACK TO DEVELOP FOR TY 13W. THIS WESTWARD TRACK IS
FORECAST UNTIL TAU 72. THE AVAILABLE DYNAMIC AIDS CONSISTING OF
NOGAPS, UKMET EGRR, JGSM, GFDN, COAMPS, AFWA MM5 AND WBAR ARE IN
FAIR AGREEMENT WITH THIS SCENARIO, WITH THE EXCEPTION OF AFWA MM5
AND NCEP GFS. NCEP GFS CONTINUES TO DEPICT A STRONGER STEERING
RIDGE POLEWARD OF THE SYSTEM AND A MORE EQUATORWARD TRACK, AS DOES
AFWA MM5. THIS FORECAST IS BASED ON A CONSENSUS OF ALL AVAILABLE
DYNAMIC AIDS. 
   C. TY 13W HAS LOST THE EYE FEATURE OVER THE PAST 06 HOURS AND
HAS EXPERIENCED A DECREASE IN DEEP CONVECTION AS OUTFLOW HAS
DECREASED SOMEWHAT. A WEAK UPPER LEVEL LOW DIRECTLY WEST OF THE
SYSTEM AND COOLER AIR HAVE SUPPRESSED THE SYSTEM AS WELL. UPPER
LEVEL CONDITIONS ARE FORECAST TO REMAIN MODERATE THROUGH TAU 24
AND THEN BEGIN TO BECOME LESS FAVORABLE AS VERTICAL WIND SHEAR
INCREASES, CAUSING A SLOW WEAKENING THROUGHOUT THE REMAINDER OF
THE FORECAST PERIOD.
   D. CURRENT WIND RADII ARE BASED ON A RECENT QUIKSCAT PASS.
FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE SIZED
SYSTEM.
   E. THE EXTENDED OUTLOOK FORECASTS TY 13W TO BEGIN TO STEER MORE
POLEWARD, TOWARD JAPAN, MAKING LANDFALL FIRST ON SHIKOKU AND THEN
NEAR HIROSHIMA. DYNAMIC AIDS REMAIN LESS CONSISTENT DURING THE
LONG RANGE FORECAST PERIOD, HOWEVER NOGAPS AND GFDN ARE NO LONGER
INDICATING A SHARP POLEWARD TURN AFTER 72 HOURS. GFS REMAINS
SIGNIFICANTLY MORE EQUATORWARD, DUE TO A STRONGER MID-LEVEL RIDGE,
AFTER 72 HOURS. TY 13W IS FORECAST TO CONTINUE TO WEAKEN, MORE
RAPIDLY AFTER TAU 96 DUE TO LAND INTERACTION.
3. FORECAST TEAM: BRYANT/FJELD/SCHULTZ//