WDPN31 PGTW 111500 
MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC 
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W WARNING NR 
04// 
RMKS/ 
1. FOR METEOROLOGISTS. 
2. PROGNOSTIC REASONING FOR 111200Z5 AUG TO 141200Z8 AUG 02. 
  A. TROPICAL DEPRESSION (TD) 18W, LOCATED APPROXIMATELY 200 NM 
EAST-NORTHEAST OF MINDANAO, HAS TRACKED NORTHWESTWARD AT 09 KNOTS 
OVER THE PAST 6 HOURS. THE WARNING POSITION IS BASED ON 111130Z7 
ENHANCED INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED 
ON SATELLITE CURRENT INTENSITY ESTIMATES OF 25 AND 30 KNOTS. 
ANIMATED ENHANCED INFRARED IMAGERY REVEALS THAT THE LOW LEVEL 
CIRCULATION CENTER REMAINS EAST OF THE DEEP CONVECTION, WHICH HAS 
DECREASED IN EXTENT OVER THE PAST 6 HOURS. 
   B. TD 18W IS EXPECTED TO DRIFT SLOWLY FROM A WEST-NORTHWESTWARD 
TRACK TO A NORTHWARD TRACK WITHIN THE MONSOON TROUGH THROUGHOUT THE 
FORECAST PERIOD. THE LOW LEVEL STEERING ENVIRONMENT REMAINS WEAK DUE 
TO COUNTERACTING STEERING OF THE EQUATORIAL WESTERLIES TO THE SOUTH 
AND EASTERLY TRADE WINDS TO THE NORTH. THE SYSTEM REMAINS IN AN 
ENVIRONMENT OF MODERATE TO HIGH VERTICAL WIND SHEAR. THE VAILABLE 
DYNAMIC AIDS CONSIST OF NOGAPS (NGPS), AVIATION (AVN), UKMET (EGRR) 
AND THE JAPANESE GLOBAL (JGSM) MODEL. EGRR INTERACTS EXCESSIVELY 
WITH A DEVELOPING TROUGH IN THE SOUTH CHINA SEA, CREATING AN 
EXAGGERATED WESTWARD TRACK. NGPS, WHICH TRACKS THE SYSTEM EASTWARD 
THROUGH THE PERIOD, EXHIBITS EXCESSIVE INTERACTION WITH TD 19W TO 
THE EAST AND DEEPENS THE SYSTEM UNREASONABLY. AVN AND JGSM TRACK THE 
SYSTEM TO THE NORTHEAST, AGAIN INTERACTING WITH 19W TO THE EAST OF 
THE SYSTEM. OUR FORECAST IS BASED ON A BLEND OF PERSISTENCE, 
CLIMATOLOGY, AND A BLEND OF ALL MODELS WITH SUBSTANTIAL ADJUSTMENTS 
IN TRACK TO ACCOUNT FOR THE AFOREMENTIONED EXCESSIVE INTERACTIONS. 
   C. TD 18W IS FORECAST TO DEVELOP AT A LESS THAN CLIMATOLOGICAL 
RATE THROUGH 48 HOURS WHILE THE SYSTEM CONTINUES TO INTERACT WITH 
THE MONSOON TROUGH AND THEN BEGIN TO WEAKEN UNDER CONTINUING 
UNFAVORABLE VERTICAL WIND SHEAR CONDITIONS.  
   D. CURRENT WIND RADII ARE BASED ON A RECENT QUIKSCAT PASS. 
FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE SIZE 
SYSTEM.
FORECAST TEAM: BRYANT/CUMMINGS/JACOBS/HEATH/SHERRY/NUTONGLA//

NNNN