Tropical Storm HAISHEN Advisory 9月4日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (HAISHEN) WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (HAISHEN), LOCATED APPROXIMATELY 542 NM
SOUTHEAST OF KADENA AB, OKINAWA, HAS TRACKED WEST-NORTHWESTWARD
AT 08 KNOTS OVER THE PAST SIX HOURS. TY 11W HAS RAPIDLY INTENSIFIED
50 KNOTS OVER THE PAST 24 HOURS FROM 75 KNOTS TO THE CURRENT
INTENSITY OF 125 KNOTS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
SHOWS A 20NM ROUND EYE, WHICH SUPPORTS THE INITIAL POSITION WITH
GOOD CONFIDENCE, AND ALSO INDICATES A SLIGHT WOBBLE TO THE TRACK
MOTION OVER THE PAST FEW HOURS AS THE SYSTEM RAPIDLY INTENSIFIED. A
031657Z AMSR2 89GHZ MICROWAVE IMAGE DEPICTS A COMPACT EYEWALL,
APPROXIMATELY 120NM DIAMETER, WITH SPIRAL BANDING OVER THE SOUTHERN
AND EASTERN SEMICIRCLES. THE INITIAL INTENSITY IS ASSESSED AT 125
KNOTS BASED ON A PGTW DVORAK ESTIMATE OF T6.5 (127 KNOTS) AND A
031638Z SATCON ESTIMATE OF 129 KNOTS; ADT ESTIMATES HAVE INCREASED
TO T6.2 (ABOUT 115-120 KNOTS) AND A 031655Z AMSR2 WINDSPEED PRODUCT
(25 KM RESOLUTION) INDICATED 106 KNOTS MAXIMUM WINDS OVER THE
EASTERN QUADRANT. UPPER-LEVEL ANALYSIS REVEALS A FAVORABLE
ENVIRONMENT WITH LOW VERTICAL WIND SHEAR (VWS) AND RADIAL OUTFLOW.
ADDITIONALLY, SST VALUES (30-31C) AND HIGH OCEAN HEAT CONTENT VALUES
ARE CONDUCIVE FOR FURTHER DEVELOPMENT. THE 03/1200Z 500MB ANALYSIS
SHOWS A DEEP MIDLATITUDE SHORTWAVE TROUGH OVER THE EAST CHINA SEA
AND WESTERN JAPAN WITH A BROAD SUBTROPICAL RIDGE ENTRENCHED NORTH OF
THE SYSTEM AND A WEAK EXTENSION OF THIS STR EXTENDING SOUTHWESTWARD
TO ABOUT 25N 130E. TY 11W IS TRACKING WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF THE DEEP-LAYERED SUBTROPICAL RIDGE (STR) AND
IS TRACKING TOWARD A COL REGION POSITIONED JUST SOUTH OF OKINAWA.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE LAST PROGNOSTIC REASONING MESSAGE.
   B. THE STR IS FORECAST TO BUILD AND REMAIN STATIONARY OVER JAPAN
WITH THE SHORTWAVE TROUGH GRADUALLY FILLING OVER THE KOREAN
PENINSULA. THE NUMERICAL MODEL TRACKERS DIVERGE NEAR OKINAWA
PRIMARILY DUE TO THE PRESENCE OF THE STR EXTENSION AND DIFFERENCES
ON HOW EACH MODEL WEAKENS THIS FEATURE. THE MODEL SPREAD NEAR
OKINAWA IS ABOUT 90NM, WHICH REFLECTS THE UNCERTAINTY IN THIS
PORTION OF THE FORECAST TRACK. THE FORECAST TRACK REMAINS HIGHLY
CONSISTENT WITH THE PREVIOUS FORECAST AND INDICATES A NORTH-
NORTHWESTWARD TRACK OVER AMAMI OSHIMA THEN JUST WEST OF KYUSHU AT
TAU 72. NUMERICAL MODEL GUIDANCE HAS REMAINED STABLE AND THE 03/12Z
ECMWF ENSEMBLE ALSO SUPPORTS THE FORECAST TRACK, HOWEVER, THE SYSTEM
COULD TRACK CLOSER TO SASEBO / KYUSHU DUE TO UNCERTAINTY IN THE
MODELS, WHICH ARE IN OVERALL FAIR AGREEMENT WITH A 100NM SPREAD IN
SOLUTIONS NEAR TAU 72. TY 11W IS FORECAST TO REACH SUPER TYPHOON
STRENGTH SHORTLY AND IS EXPECTED TO MAINTAIN THIS INTENSITY THROUGH
TAU 36 WITH GRADUAL WEAKENING AS THE SYSTEM TRACKS POLEWARD.
   C. IN THE EXTENDED PERIOD, NUMERICAL MODEL GUIDANCE DIVERGES WITH
INCREASING UNCERTAINTY IN THE EXACT TRACK OVER SOUTH KOREA. TY 11W
IS FORECAST TO BEGIN EXTRA-TROPICAL TRANSITION (ETT) NEAR TAU 72 AS
IT INTERACTS WITH THE SHORTWAVE TROUGH AND WILL ACCELERATE POLEWARD
AND COMPLETE ETT BY TAU 120 WHEN IT GAINS FRONTAL CHARACTERISTICS
OVER NORTH KOREA. SIGNIFICANT WEAKENING WILL OCCUR OVER THE KOREAN
PENINSULA DUE TO INCREASING VWS AND INTERACTION WITH MOUNTAINOUS
TERRAIN. OVERALL, THERE IS MODERATE CONFIDENCE IN THE JTWC FORECAST
TRACK, WHICH IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS.//
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