Tropical Storm DOLPHIN Advisory 9月21日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (FOURTEEN)
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 14W (FOURTEEN), LOCATED APPROXIMATELY 361 NM
EAST-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWARD
AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY SHOWS THE SYSTEM HAS BEGUN TO ELONGATE NW-SE
WITH SLIGHTLY DEEPENED CENTRAL CONVECTION THAT IS OFFSET TO THE
NORTH AND EAST OF A PARTLY OBSCURED LOW LEVEL CIRCULATION (LLC).
THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON A
DEFINED LLC IN THE 201620Z ATMS PASS THAT IS ALSO DISPLACED FROM THE
ASSOCIATED CONVECTION. THE INITIAL INTENSITY OF 40 KTS IS HELD
SLIGHTLY HIGHER THAN THE DVORAK INTENSITY ESTIMATES OF T2.5/35KTS
FROM PGTW AND KNES AND REFLECTS THE SLIGHTLY IMPROVED EIR STRUCTURE.
ANALYSES INDICATE THE SYSTEM HAS SUBTROPICAL CHARACTERISTICS AND
REMAINS QUASI-STATIONARY (QS) UNDER DUAL OUTFLOW CHANNELS WITH A
STRONG POLEWARD BIAS. THIS IS PROVIDING VENTILATION TO THE DEEP
CONVECTION. SEA SURFACE TEMPERATURES (SST) AT 30-31C ARE ALSO WARM
AND CONDUCIVE. HOWEVER, MODERATE (15-20KT) VERTICAL WIND SHEAR AND
SUBSIDENCE ALONG THE NORTHWEST PERIPHERIES AHEAD OF A SHORTWAVE
TROUGH ARE OFFSETTING THESE FAVORABLE DYNAMICS. THE CYCLONE IS IN A
COL BETWEEN THE SUBTROPICAL RIDGE (STR) TO THE NORTHEAST AND THE STR
TO THE WEST.
3. FORECAST REASONING.
   A. THE EXTRATROPICAL TRANSITION (ETT) IS NOW EXPECTED TO OCCUR
SOONER, AT TAU 36, OTHERWISE, THERE IS NO SIGNIFICANT CHANGE TO THE
FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 14W WILL SLOWLY DRIFT NORTHWARD AWAY FROM THE COL AS THE
STR TO THE NE ASSUMES STEERING. THE AFOREMENTIONED MARGINALLY
FAVORABLE CONDITIONS WILL FUEL SLIGHT INTENSIFICATION TO 50 KTS BY
TAU 36. CONCURRENTLY, BY TAU 12, THE SYSTEM WILL BEGIN ETT AND BY
TAU 36 WILL BECOME FULL ET AS IT GETS ABSORBED INTO A QS FRONTAL
BOUNDARY SOUTH OF JAPAN. NUMERICAL MODELS ARE IN FAIRLY TIGHT
AGREEMENT UP TO TAU 36 BUT GIVEN THE TENTATIVE STORM MOTION IN THE
COL AND THE UNCERTAINTY OF EVENTUAL NORTHWARD TRACK, THERE IS LOW
CONFIDENCE IN THE JTWC FORECAST TRACK.//
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