WDPN31 PGTW 261500
MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W
/WARNING NR 02//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 261200Z1 TO 291200Z4 AUG 2004.
   A. TROPICAL DEPRESSION (TD) 21W, LOCATED APPROXIMATELY 320 NM
EAST OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-NORTHWESTWARD AT
12 KNOTS OVER THE PAST 06 HOURS. THE WARNING POSITION
IS BASED ON 261130Z3 INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY
IS BASED ON SATELLITE CURRENT INTENSITY ESTIMATES OF 25, 30 AND
35 KNOTS. 
   B. TD 21W IS FORECAST TO CONTINUE TRACKING WESTWARD ALONG
THE SOUTHERN PERIPHERY OF THE LOW TO MID-LEVEL STEERING RIDGE
LOCATED TO THE NORTH. DUE TO THE WEAK NATURE OF TD 21W, THERE
ARE LIMITED DYNAMIC AIDS AVAILABLE CONSISTING OF ONLY UKMET EGRR,
JGSM, WBAR AND NOGAPS. THESE AIDS ARE IN FAIR AGREEMENT, WITH NOGAPS
FORECASTING THE SYSTEM TO TRACK SOUTHWESTWARD WHILE JTYM FORECASTS
A MORE POLEWARD SOLUTION DUE TO A WEAKER STEERING RIDGE. THIS
FORECAST IS BASED ON A BLEND OF THE LIMITED AVAILABLE DYNAMIC AIDS. 
   C. REVIEW OF THE CURRENT AND FORECASTED UPPER AIR ENVIRONMENT
REVEALS THAT TD 21W WILL PERSIST IN A REGION OF LINEAR TO CONFLUENT
FLOW FROM THE NORTHEAST. TD 21W WILL ALSO FOLLOW IN THE WAKE OF
TY 19W WHICH SHOULD HAVE SUFFICIENTLY MIXED THE DEEP LAYER OF
WARM WATER UP ENOUGH TO REDUCE CLIMATOLOGICAL INTENSIFICATION
POTENTIAL. FOR THESE REASONS, TD 21W IS FORECAST TO INTENSIFY VERY
SLOWLY FOR THE FIRST HALF OF THE FORECAST PERIOD. MIDWAY THROUGH THE
FORECAST PERIOD, TD 21W WILL BEGIN TO ENCOUNTER INCREASED VERTICAL
SHEAR FROM THE OUTFLOW OF TY 19W. THIS UNFAVORABLE ENVIRONMENT
WILL CAUSE TD 21W TO WEAKEN.
   D. CURRENT WIND RADII AND FORECAST WIND RADII ARE BASED ON
CLIMATOLOGY FOR A NEW SYSTEM.
3. FORECAST TEAM: GRUBER/KLINZMANN/HEILER//