WDPN32 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 20W (TWENTY), LOCATED APPROXIMATELY 90 
NM WEST-NORTHWEST OF IWO TO, HAS TRACKED EAST-NORTHEASTWARD AT 05 
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED 
SATELLITE IMAGERY REVEALS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION 
CENTER (LLCC) WITH FLARING DEEP CONVECTION LOCATED OVER THE 
SOUTHEASTERN SEMICIRCLE. A 201612Z AMSR2 89GHZ COLOR COMPOSITE 
MICROWAVE IMAGE SHOWS AN EXPOSED LLCC POSITIONED ALONG THE 
NORTHWESTERN EDGE OF THE FLARING DEEP CONVECTION, WHICH SUPPORTS THE 
INITIAL POSITION WITH FAIR CONFIDENCE. RECENT ASCAT DATA (25-30 
KNOTS) AS WELL AS A 201610Z AMSR2 WINDSPEED IMAGE SHOWING MAXIMUM 
WINDS OF 28 KNOTS SUPPORT THE INITIAL INTENSITY ASSESSMENT OF 30 
KNOTS. ENVIRONMENTAL ANALYSIS REVEALS TD 20W IS CURRENTLY IN A 
MARGINAL ENVIRONMENT FOR DEVELOPMENT WITH STRONG (35-40 KNOTS) 
WESTERLY VERTICAL WIND SHEAR (VWS) OFFSET BY WARM (28C) SEA SURFACE 
TEMPERATURES AND VIGOROUS EQUATORWARD OUTFLOW ALOFT. TD 20W IS 
TRACKING SLOWLY EAST-NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY 
OF A WEAKENED LOW LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO THE 
EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TD 20W IS EXPECTED TO CONTINUE TRACKING SLOWLY AND ERRATICALLY 
WITHIN THIS WEAK STEERING ENVIRONMENT THROUGH TAU 24. AFTER TAU 24, 
A SHORTWAVE TROUGH POSITIONED TO THE NORTH WILL PROPAGATE EASTWARD 
ALLOWING THE STR TO BUILD AND REORIENT POLEWARD. CONSEQUENTLY THE 
SYSTEM SHOULD ACCELERATE NORTHWARD ALONG THE WESTERN PERIPHERY OF 
THE STR THROUGH TAU 48. TD 20W WILL GRADUALLY WEAKEN THROUGH THE 
FORECAST PERIOD WITH DISSIPATION ANTICIPATED BY TAU 48 DUE TO 
PERSISTENT STRONG (40-45 KNOTS) VWS. THE REMNANTS OF THE SYSTEM WILL 
BE ABSORBED INTO A DEVELOPING FRONT WELL SOUTHEAST OF THE KANTO 
PLAIN. NUMERICAL MODEL GUIDANCE REMAINS IN GOOD AGREEMENT, HOWEVER, 
DUE TO THE INITIAL ERRATIC TRACK THERE IS OVERALL FAIR CONFIDENCE IN 
THE JTWC FORECAST TRACK WHICH LIES NEAR THE MULTI-MODEL CONSENSUS.//
NNNN