JTWC Storm Progs

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WDPN31 PGTW 131500

MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC//

SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W WARNING NR 15//

RMKS/

1. FOR METEOROLOGISTS.

2. PROGNOSTIC REASONING FOR 131200Z7 TO 181200Z2 DEC 2004.

A. TROPICAL STORM (TS) 31W (TALAS), LOCATED APPROXIMATELY 180 NM

SOUTH-SOUTHWEST OF GUAM, HAS TRACKED WESTWARD AT 16 KNOTS OVER THE

PAST 06 HOURS. THE WARNING POSITION IS BASED ON 131130Z9 ENHANCED

INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED ON SATEL-

LITE CURRENT INTENSITY ESTIMATES OF 45 KNOTS FROM ALL FIXING AGENCIES.

B. TS 31W IS FORECAST TO TRACK WEST-NORTHWESTWARD ALONG THE SOUTH-

WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE ANCHORED TO THE NORTH FOR

THE NEXT 12 TO 18 HOURS. AS A TROUGH MOVES EASTWARD OVER THE EAST CHINA

SEA, WEAKENING THE SUBTROPICAL RIDGE, TS 31W WILL BEGIN TO TRACK NORTH-

WESTWARD AND STEADILY DECREASE IT'S SPEED OF ADVANCE AS IT MOVES

POLEWARD. THE AVAILABLE DYNAMIC AIDS CONSISTING OF NOGAPS, EGRR, GFDN,

JGSI, JTYI, AVN, COAMPS, MM5, TCLAPS, AND WBAR ARE IN FARILY GOOD

AGREEMENT FOR THE FIRST 36 TO 48 HOURS WITH THE EXCEPTION OF TCLAPS,

THE POLEWARD OUTLIER, MM5 AND JGSI WHICH ARE EQUATORWARD OUTLIERS.

TCLAPS INDICATES AN IMMEDIATE WEAKNESS IN THE SUBTROPICAL RIDGE. MM5

AND JGSI INDICATE THE STEERING RIDGE TO BUILD WESTWARD KEEPING TS 31W

ON A WESTWARD TRACK. THIS FORECAST IS BASED ON A CONSENSUS OF ALL

AVAILABLE DYNAMIC AIDS WITH LESS EMPHASIS ON TCLAPS, MM5 AND JGSI.

C. TS 31W IS FULLY EXPOSED WITH THE DEEPEST CONVECTION LOCATED

NORTHWEST OF THE SYSTEM AND HAS WEAKENED IN THE PAST 06 HOURS. THE

INTENSITY IS FORECAST TO SLIGHTLY INCREASE AS THE SYSTEM TRACKS NORTH-

WESTWARD. EXPECT UPPER LEVEL OUTFLOW TO INCREASE, BUT BE OFFSET BY

INCREASING VERTICAL WIND SHEAR. TS 31W IS EXPECTED TO INCREASE AT

LESS THAN A CLIMATOLOGICAL RATE.

D. CURRENT WIND RADII ARE BASED ON A 130625Z7 QUIKSCAT PASS.

FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE SIZED

SYSTEM.

E. IN THE EXTENDED FORECAST TS 31W IS FORECAST TO BEGIN RECURVING

POLEWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE AS

A SHORT WAVE TROUGH MOVES OVER EASTERN CHINA. HOWEVER, CONFIDENCE IN

THE MODELS DURING THE LATE PERIOD OF THE FORECAST IS LOW DUE TO A WIDE

SPREAD IN THE MODELS.

3.FORECAST TEAM: PITTS/KLINZMANN/FUNK//

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