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Pacific T.S. TALAS Prognosis


Jeb
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WDPN31 PGTW 120300

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

SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W

/WARNING NR 09//

RMKS/

1. FOR METEOROLOGISTS.

2. PROGNOSTIC REASONING FOR 120000Z3 TO 170000Z8 DEC 2004.

A. TROPICAL STORM (TS) 31W (TALAS), LOCATED APPROXIMATELY 665 NM

EAST-SOUTHEAST OF GUAM, HAS TRACKED WESTWARD AT 16 KNOTS OVER THE

PAST 06 HOURS. THE WARNING POSITION IS BASED ON 112330Z0 MULTISPEC-

TRAL SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED ON SATELLITE

CURRENT INTENSITY ESTIMATES OF 45 AND 55 KNOTS. RECENT ANIMATED

MULTISPECTRAL IMAGERY REVEALS A FULLY EXPOSED LOW LEVEL CIRCULATION

CENTER. SINCE THE 111800Z3 FIXES WERE BASED ON ENHANCED INFRARED

IMAGERY AND VISIBLE IMAGERY IS NOW AVAILABLE, THE SYSTEM SPEED IS NOT

AS FAST AS PREVIOUSLY FORECAST. HOWEVER, ENHANCED INFRARED IMAGERY

SHOWS THE DEEP CONVECTION HAS DECREASED DURING THE PREVIOUS 06 HOURS

AND CONTINUES TO BE CONFINED TO THE WESTERN PERIPHERY.

B. DURING THE NEXT 24 TO 36 HOURS, TS 31W IS FORECAST TO TRACK

WEST-NORTHWESTWARD AROUND THE SOUTHWESTERN PERIPHERY OF THE STEERING

RIDGE. AS THE SYSTEM CONTINUES TO GAIN LATITUDE, THE FORWARD SPEED

IS EXPECTED TO GRADUALLY DECREASE. AFTER TAU 48, A WEAKNESS IN THE

SUBTROPICAL RIDGE AXIS IS EXPECTED TO DEVELOP OVER THE PHILIPPINE

SEA, AND TS 31W SHOULD TRACK TOWARD THIS WEAKNESS. THE AVAILABLE

DYNAMIC AIDS CONSISTING OF NOGAPS, JGSM, MM5, WBAR, COAMPS, EGRR,

GFDN, AND AVN ARE IN DECENT AGREEMENT UP TO TAU 36. AFTER THIS TIME,

THE AIDS BEGIN TO DIVERGE WITH EGRR AND COAMPS DEPICTING MORE OF A

POLEWARD SOLUTION WHILE NOGAPS AND JGSM DEPICT MORE OF A WESTWARD

SOLUTION. THIS FORECAST IS BASED ON A CONSENSUS OF ALL AVAILABLE

DYNAMIC AIDS WITH LESS EMPHASIS ON EGRR.

C. THE INTENSITY OF TS 31W IS FORECAST TO GRADUALLY INCREASE DUE

TO AN ENVIRONMENT OF MODERATE VERTICAL WIND SHEAR. AFTER TAU 72, A

REGION OF MODERATE TO HIGH VERTICAL WIND SHEAR WILL START TO WEAKEN

TS 31W. POLEWARD OUTFLOW SHOULD REMAIN FAVORABLE, HOWEVER THE IN-

CREASED SHEAR WILL OFFSET THE OUTFLOW.

D. CURRENT WIND RADII ARE BASED ON A 111417Z5 TRMM MICROWAVE PASS.

FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE SIZED

SYSTEM.

E. DURING THE EXTENDED TAUS, TS 31W IS FORECAST TO MOVE INTO A

WEAKER STEERING ENVIRONMENT AS A MAJOR SHORTWAVE TROUGH STARTS TO

BREAK DOWN THE PREDOMINANT STEERING FLOW. THE DYNAMIC AIDS ALSO BEGIN

TO DIVERGE GREATLY WITH NOGAPS AND EGRR AS THE MOST EXTREME OUTLIERS.

NOGAPS DEPICTS A STRONGER RIDGE WHICH PROMOTES A MORE NORTHWESTWARD

TRACK. HOWEVER, EGRR DEPICTS A STRONGER WEAKNESS IN THE RIDGE WHICH

PROMOTES A RECURVATURE SOLUTION. GIVEN THE HIGH DIVERGENCE IN THE

MODELS, CONFIDENCE IN THE EXTENDED FORECAST IS LOW.

3.FORECAST TEAM: LEFFLER/RONSSE/LEWIN//

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