Tropical Storm ATSANI Advisory 11月7日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) WARNING NR
034//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 23W (ATSANI), LOCATED APPROXIMATELY 192 NM
SOUTH-SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED NORTHWESTWARD AT 06
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY DEPICTS A COMPACT (55-60NM CORE), CONSOLIDATING
SYSTEM WITH TIGHTLY-CURVED BANDING WRAPPING INTO A DEFINED LOW-LEVEL
CIRCULATION CENTER (LLCC). THERE ARE NO MICROWAVE IMAGES AVAILABLE,
HOWEVER, RADAR IMAGERY REVEALS A WELL-ORGANIZED SYSTEM WITH AN EYE-
LIKE STRUCTURE AND SPIRAL BANDING OVER THE EASTERN SEMICIRCLE. EIR
IMAGERY HAS YET TO SHOW THE PRESENCE OF AN EYE AND INDICATES A
SLIGHT DEGRADATION OF STRUCTURE SINCE 062000Z. OVERALL, CONFIDENCE
IN THE INITIAL POSITION IS GOOD. A RECENT (060947Z) SMAP IMAGE
SHOWED MAXIMUM 10-MINUTE SUSTAINED WINDS OF 51-55 KNOTS AND THIS
DATA ALONG WITH A PGTW DVORAK PATTERN-T ESTIMATE OF 3.5 (55 KNOTS)
SUPPORT THE INITIAL INTENSITY ASSESSMENT OF 55 KNOTS. THIS ESTIMATE
IS CONSISTENT WITH THE CONVECTIVE STRUCTURE ALTHOUGH OBJECTIVE AND
SUBJECTIVE DVORAK DATA-T ESTIMATES ARE GENERALLY LOWER AT 2.5 TO 3.0
(35-45 KNOTS) LIKELY DUE TO THE SMALL SIZE OF THE SYSTEM. LOW TO
MODERATE (15-20 KT) VERTICAL WIND SHEAR (VWS), WARM (26-27 CELSIUS)
SEA SURFACE TEMPERATURES (SST), AND ENHANCED POLEWARD OUTFLOW ARE
CONTRIBUTING TO AN OVERALL MARGINALLY-FAVORABLE ENVIRONMENT AS TS
23W TRACKS SLOWLY ALONG THE SOUTHERN PERIPHERY OF A WEAK SUBTROPICAL
RIDGE (STR) POSITIONED TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 23W IS EXPECTED TO CONTINUE TRACKING SLOWLY WEST-
NORTHWESTWARD TO WESTWARD THROUGH TAU 12 UNDER A WEAKENED MID-LEVEL
STR. AFTER TAU 12, LOW-LEVEL RIDGING ASSOCIATED WITH A NORTHEAST
SURGE EVENT IS FORECAST TO STRENGTHEN OVER THE EAST CHINA SEA, WHICH
WILL LEAD TO A SHARP SOUTHWESTWARD TURN AND ACCELERATED TRACK
THROUGH TAU 72. THE SYSTEM IS FORECAST TO WEAKEN THROUGH THE
FORECAST PERIOD AS VWS INCREASES TO 30-40 KNOTS WITH COOLER SST
VALUES (24-26C). TS 23W SHOULD WEAKEN RAPIDLY AFTER TAU 36 WITH
DISSIPATION EXPECTED BY TAU 72 BUT PERHAPS SOONER AS THE ENVIRONMENT
DEGRADES. DESPITE THE COMPLEX, EVOLVING STEERING PATTERN, NUMERICAL
MODEL GUIDANCE IS IN FAIR AGREEMENT WITH MAJOR DIFFERENCES IN THE
TIMING OF DISSIPATION. THE BULK OF THE GUIDANCE SUPPORTS THE
SOUTHWESTWARD TRACK ASSOCIATED WITH THE NORTHEAST SURGE EVENT.
OVERALL, THERE IS FAIR CONFIDENCE IN THE JTWC FORECAST TRACK WHICH
IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS THROUGH TAU 36.//
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