WDPN31 PGTW 050300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (DUJUAN)/
WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
    A. TROPICAL STORM (TS) 13W (DUJUAN), LOCATED APPROXIMATELY 450 
NM SOUTHEAST OF OKINAWA, JAPAN, HAS TRACKED NORTHEASTWARD AT 08 
KNOTS OVER THE PAST SIX HOURS. RECENT ANIMATED MULTISPECTRAL 
SATELLITE IMAGERY SHOWS DEEP CONVECTION DEVELOPING OVER AN IMPROVING 
LOW LEVEL CIRCULATION CENTER. ANIMATED WATER VAPOR IMAGERY SUGGESTS 
THAT INCREASING POLEWARD OUTFLOW HAS AIDED THIS RECENT CONVECTIVE 
DEVELOPMENT. THE CURRENT POSITION IS BASED ON A 042330Z PGTW FIX AND 
A 042245Z SSMI PASS. THE CURRENT INTENSITY ESTIMATE OF 40 KNOTS IS 
CONSISTENT WITH DVORAK T-NUMBER VALUES OF 3.0 FROM PGTW AND 2.5 FROM 
KNES.
3. FORECAST REASONING.
    A. THE GENERAL FORECAST PHILOSOPHY HAS NOT CHANGED SINCE THE 
PREVIOUS PROGNOSTIC REASONING BULLETIN. HOWEVER, EXTENDED RANGE 
TRACK SPEEDS (TAU 96 THROUGH TAU 120) HAVE BEEN INCREASED IN 
ANTICIPATION OF A MORE RAPID TRANSITION INTO THE MIDLATITUDE 
WESTERLY FLOW PATTERN THAN PREVIOUSLY EXPECTED.
    B. TS 13W IS EXPECTED TO TRACK INCREASINGLY POLEWARD OVER THE 
NEXT 48 HOURS UNDER THE CONTINUED STEERING INFLUENCE OF SUBTROPICAL 
RIDGING TO THE EAST. AFTER TAU 48 THE TROPICAL STORM WILL CREST THE 
STEERING RIDGE AXIS AND TURN NORTHEASTWARD AHEAD OF AN APPROACHING 
MIDLATITUDE TROUGH. THE TROPICAL STORM SHOULD INTENSIFY STEADILY 
OVER THE NEXT 36 HOURS AS POLEWARD AND EQUATORWARD OUTFLOW ALOFT 
REMAIN FAVORABLE. HOWEVER, THE CYCLONE IS EXPECTED TO APPROXIMATELY 
MAINTAIN INTENSITY BETWEEN TAU 36 AND TAU 72 AS WESTERLY VERTICAL 
WIND SHEAR BEGINS TO INCREASE.
    C. TS 13W WILL ACCELERATE INTO THE MIDLATITUDE WESTERLY FLOW 
PATTERN AFTER TAU 72, STARTING EXTRATROPICAL TRANSITION BY TAU 96 
AND BECOMING FULLY BAROCLINIC BY TAU 120. VERTICAL WIND SHEAR WILL 
INCREASE SIGNIFICANTLY DURING THIS EXTENDED PERIOD, RESULTING IN A 
STEADY WEAKENING TREND AS THE CYCLONE ACCELERATES NORTHEASTWARD. THE 
AVAILABLE NUMERICAL MODEL GUIDANCE HAS COME INTO GOOD AGREEMENT WITH 
THE CURRENT FORECAST.
FORECAST TEAM: CHARLIE.//
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