Tropical Storm YUTU Advisory 10月31日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (YUTU) WARNING NR
38//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 31W (YUTU), LOCATED APPROXIMATELY 430 NM
SOUTHEAST OF HONG KONG, HAS TRACKED WESTWARD AT 05 KNOTS OVER THE
PAST SIX HOURS. TS 31W HAS CONTINUED TO TRACK AWAY FROM THE
PHILIPPINES WITH DECREASING FRICTIONAL EFFECTS. CONSEQUENTLY,
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A
RECONSOLIDATING SYSTEM WITH IMPROVED DEEP CONVECTIVE BANDING,
ESPECIALLY OVER THE NORTHERN SEMICIRCLE, WRAPPING INTO A BROAD LOW-
LEVEL CIRCULATION CENTER. A 301904Z SSMI 37GHZ IMAGE DEPICTS TIGHTLY
CURVED SHALLOW BANDING WRAPPING INTO A WELL-DEFINED MICROWAVE EYE
FEATURE, WHICH SUPPORTS THE CURRENT POSITION WITH GOOD CONFIDENCE
(WITHIN 30NM). A RECENT ASCAT AMBIGUITY IMAGE AS WELL AS THE RECENT
SSMI IMAGE SUGGEST A SOMEWHAT ERRATIC TRACK OVER THE PAST 12 HOURS
WITH A DIP TO THE WEST-SOUTHWEST FOLLOWED BY THE RECENT SHARP TURN
TO THE NORTHWEST. OVERALL, ENVIRONMENTAL CONDITIONS ARE FAVORABLE
WITH LOW (10-15 KT) VERTICAL WIND SHEAR AND ENHANCED POLEWARD
OUTFLOW. TS 31W IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF THE
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE. THE 34-KNOT WIND RADII OVER
THE NORTHWEST (ANALYSIS) AND NORTHEAST QUADRANTS (FORECAST) HAVE
BEEN MODIFIED TO INCORPORATE NORTHEAST SURGE WINDS ADJACENT TO THE
SYSTEM.
   B. TS 31W IS FORECAST TO TRACK NORTH-NORTHWESTWARD TO NORTHWARD
THROUGH THE FORECAST PERIOD AS IT TRACKS ALONG THE WESTERN
PERIPHERY OF THE STR. THE SYSTEM IS FORECAST TO REINTENSIFY TO A
PEAK OF 65 KNOTS BY TAU 24 DUE TO THE FAVORABLE ENVIRONMENTAL
CONDITIONS. AFTER TAU 24, INCREASING VERTICAL WIND SHEAR (VWS) AND
SLIGHTLY COOLER SST VALUES (26C) WILL SERVE TO GRADUALLY WEAKEN THE
SYSTEM. AFTER TAU 48, TS 31W WILL RAPIDLY DISSIPATE OVER WATER DUE
TO DRY AIR ENTRAINMENT, STRONG VWS AND UPPER-LEVEL CONVERGENCE.
THERE IS HIGH UNCERTAINTY IN THE JTWC FORECAST TRACK WITH A LARGE
SPREAD OF 530NM AT TAU 72. MOST OF THE MODELS RAPIDLY DISSIPATE
THE SYSTEM, EITHER SLOWING THE FORWARD MOTION WHILE LOSING THE
CIRCULATION OR EJECTING THE REMNANT CIRCULATION NORTHEASTWARD INTO
THE BAROCLINIC ZONE AND STRONG UPPER-LEVEL WESTERLIES. THE JTWC
OFFICIAL FORECAST FAVORS A DISSIPATION SCENARIO AND SLOWER TRACK
SPEEDS OVER THE NORTHERN SOUTH CHINA SEA DUE TO THE VERY UNFAVORABLE
ENVIRONMENTAL CONDITIONS.//
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