Tropical Storm CHAN-HOM Advisory 10月8日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (CHAN-HOM) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 16W (CHAN-HOM), LOCATED APPROXIMATELY 281 NM
EAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 09 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS
FLARING CONVECTION PRIMARILY LOCATED POLEWARD OF A LARGE AND RAGGED
30-NM EYE. THE SOUTHWESTERN EYE WALL HAS BECOME DISCONTINUOUS WITH
SOME DRY AIR ENTRAINMENT OBSERVED. THE INITIAL WIND RADII CONTINUE
TO CAPTURE BOTH THE TROPICAL CYCLONE WINDS AND A PORTION OF THE
NORTHEASTERLY FRONTAL FLOW WRAPPING INTO THE SYSTEM. THE INITIAL
INTENSITY REMAINS ASSESSED AT 70 KNOTS BASED ON AN AVERAGE OF
PGTW/KNES DVORAK INTENSITY ESTIMATES OF T4.5 (77 KNOTS) AND AN RJTD
ESTIMATE OF T4.0 (65 KNOTS). ENVIRONMENTAL CONDITIONS REMAIN
FAVORABLE WITH ENHANCED POLEWARD OUTFLOW, GOOD EQUATORWARD OUTFLOW,
LOW (5-10 KT) VERTICAL WIND SHEAR (VWS), AND WARM (28-29 CELSIUS)
SEA SURFACE TEMPERATURES. THE SYSTEM IS TRACKING ALONG THE
SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO
THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE. IMPORTANT NOTE: TY 16W HAS MAINTAINED
EXTENSIVE GALE-FORCE WINDS AS LARGE AS 240NM RADIUS. TO FURTHER
COMPLICATE THIS SCENARIO, THE SYSTEM IS TRACKING INTO A STRONG
BAROCLINIC ZONE WITH ITS OWN TIGHT GRADIENT AS EVIDENCED BY 30 TO 40
KNOT SURFACE WIND REPORTS ACROSS WESTERN JAPAN AND THE RYUKYU
ISLANDS. THUS, GALE-FORCE WINDS ARE POSSIBLE ALONG AND OUTSIDE THE
PERIPHERY OF THE SYSTEM AS IT TRACKS CLOSER TO JAPAN.
   B. TY 16W HAS BEGUN TO TURN POLEWARD AND IS FORECAST TO TRACK
NORTHWESTWARD TO NORTHWARD THROUGH TAU 36 AS IT RECURVES. NUMERICAL
MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT, BUT THERE IS STILL
UNCERTAINTY WITH HOW TIGHT THE TURN TOWARD THE NORTHEAST WILL BE,
WHICH WILL GREATLY INFLUENCE THE POTENTIAL IMPACTS TO MAINLAND
JAPAN. AFTER TAU 36, THE SYSTEM WILL ACCELERATE NORTHEASTWARD AS IT
BEGINS TO INTERACT WITH THE MIDLATITUDE WESTERLIES. THE TRACK
UNCERTAINTY IS EXACERBATED BY THE HIGH ZONAL FLOW, RESULTING IN THE
EXPECTED SHARP TURN TOWARD THE NORTHEAST. TY 16W IS FORECAST TO
INTENSIFY TO A PEAK INTENSITY OF 80 KNOTS BY TAU 24 GIVEN THE
FAVORABLE ENVIRONMENTAL CONDITIONS, BUT THE CURRENT DISORGANIZATION
OF THE INNER CORE OF TY 16W COULD PREVENT ANY FURTHER
INTENSIFICATION FROM OCCURRING. BASED ON THE ZONAL STEERING PATTERN
AND SPREAD IN SOLUTIONS, THERE IS FAIR CONFIDENCE IN THIS PORTION OF
THE JTWC FORECAST TRACK.
   C. AFTER TAU 72, THE SYSTEM WILL ACCELERATE EAST-NORTHEASTWARD
ALONG AND NEAR THE SOUTHERN COAST OF JAPAN. DUE TO HIGH VERTICAL
WIND SHEAR (>35 KTS), TY 16W IS EXPECTED TO WEAKEN STEADILY FOR THE
REMAINDER OF THE FORECAST PERIOD TO AN INTENSITY OF 50 KTS BY TAU
96. TY 16W WILL COMPLETE EXTRATROPICAL TRANSITION (ETT) BY TAU 96 AS
IT GETS ABSORBED INTO THE BAROCLINIC ZONE. THE JTWC FORECAST
TRACK CLOSELY FOLLOWS THE MULTI-MODEL CONSENSUS. DUE TO UNCERTAINTY
IN THE TRACK AS THE SYSTEM UNDERGOES ETT, THERE IS FAIR CONFIDENCE
IN THE JTWC FORECAST TRACK. ALL INTERESTS IN THE KANTO PLAIN REGION
OF JAPAN SHOULD PAY CLOSE ATTENTION TO THE TIMING OF THE
NORTHEASTWARD TURN AND EVOLUTION OF THE WIND FIELD, GIVEN THE
POSSIBILITY THAT ANY MINOR FORECAST TRACK SHIFT TOWARD THE WEST
WOULD BRING THE CORE OF TY 16W ASHORE.//
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