WDPN31 PGTW 100300
MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W WARNING NR 05//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 100000Z TO 150000Z OCT 2006.
   A. TROPICAL STORM (TS) 21W (SOULIK), LOCATED APPROXIMATELY 470 NM
EAST-NORTHEAST OF SAIPAN HAS TRACKED WEST-NORTHWESTWARD AT 13 KNOTS
OVER THE PAST SIX HOURS.
   B. TS 21W IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A
SUBTROPICAL RIDGE (STR) ANCHORED NORTH OF WAKE ISLAND. THE MID-
LATITUDE TROUGH NORTH OF THE SYSTEM WILL CONTINUE MOVING EASTWARD,
ALLOWING THE STR TO RE-ORIENT AND STEER TS 21W WEST-NORTHWESTWARD
THROUGH TAU 48. AROUND TAU 72, ANOTHER MID-LATITUDE TROUGH WILL PASS
TO THE NORTH OF TS 21W, CAUSING THE TRACK TO TEMPORARILY SHIFT
POLEWARD BEFORE RETURNING TO A WESTERLY TRACK. THIS FORECAST IS
BASED ON A CONSENSUS OF ALL AVAILABLE DYNAMIC AIDS, WHICH ARE IN
GOOD AGREEMENT THROUGH TAU 72.
   C. TS 21W WILL INTENSIFY AT A LESS THAN CLIMATOLOGICAL RATE
THROUGHOUT THE MAJORITY OF THE FORECAST DUE TO MODERATE VERTICAL
WIND SHEAR AND RESTRICTED OUTFLOW ALOFT. FROM TAU 48 TO TAU 72,
THE SYSTEM WILL TEMPORARILY INTENSIFY AT A FASTER RATE DUE TO
IMPROVED POLEWARD OUTFLOW AND DECREASED VERTICAL WIND SHEAR.
   D. CURRENT WIND RADII ARE BASED ON A 092033Z SSMI IMAGE AND
A 091858 QUIKSCAT IMAGE. FORECAST WIND RADII ARE BASED ON
CLIMATOLOGY FOR AN AVERAGE-SIZED SYSTEM.
   E. FROM TAU 72, SOME UNCERTAINTY EXISTS CONCERNING THE TIMING OF
THE INTERACTION WITH THE MIDLATITUDE TROUGH. THE MAJORITY OF THE
LONG-RANGE AIDS PREDICT A TEMPORARY TURN POLEWARD AND THEN A RETURN
TO WESTERLY MOVEMENT. ONLY THE EGRR PREDICTS RECURVATURE BETWEEN TAU
72 AND TAU 96 DUE TO ITS MORE NORTHERLY STORM POSITION. THE EXTENDED
FORECAST IS BASED ON A CONSENSUS OF ALL AVAILABLE OBJECTIVE AIDS
WITH LESS EMPHASIS ON EGRR AND MORE EMPHASIS ON THE MAJORITY,
WESTWARD-TRACK GROUPING. 
FORECAST TEAM: CHARLIE//
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