Tropical Storm TWENTY Advisory 10月21日

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.//
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