WDPN32 PGTW 210300 COR
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) 
WARNING NR 003A CORRECTED//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 20W (TWENTY), LOCATED APPROXIMATELY
77 NM WEST OF IWO TO, HAS TRACKED SOUTHEASTWARD AT 03 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS 
A FULLY EXPOSED, WELL DEFINED LOW LEVEL CIRCULATION CENTER WITH 
ISOLATED DEEP CONVECTION DISPLACED TO THE SOUTHEAST, WHICH SUPPORTS 
THE INITIAL POSITION WITH GOOD CONFIDENCE. A 202259Z ASCAT-A 
BULLSEYE IMAGE REVEALS A DEFINED, SYMMETRIC CIRCULATION WITH 25-30 
KNOT WINDS OVER THE NORTHWEST QUADRANT, WHICH SUPPORTS 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 SOUTHEASTWARD ALONG THE 
NORTHEASTERN PERIPHERY OF A WEAKENED LOW LEVEL SUBTROPICAL RIDGE 
(STR) POSITIONED TO THE WEST.
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 12. AFTER TAU 12, 
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 36. TD 20W WILL GRADUALLY WEAKEN THROUGH THE 
FORECAST PERIOD WITH DISSIPATION ANTICIPATED BY TAU 36 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.
4. JUSTIFICATION FOR CORRECTION: UPDATED DIRECTION OF SYSTEM MOVEMENT 
AND STEERING MECHANISM IN PARA 2.//
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