Tropical Storm YUTU Advisory 10月26日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 31W (YUTU) WARNING NR
18//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 31W (YUTU), LOCATED APPROXIMATELY 267 NM
NORTHWEST OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-NORTHWESTWARD AT
09 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY INDICATES A GRADUAL WEAKENING TREND WITH AN
ASYMMETRIC CONVECTIVE STRUCTURE, HOWEVER, RECENT EIR SHOWS A RE-
DEVELOPING, IRREGULAR EYE. THIS WEAKENING TREND IS PRIMARILY
ASSOCIATED WITH AN EYEWALL REPLACEMENT CYCLE, WHICH APPEARS TO HAVE
NOW COMPLETED AS EVIDENT IN A 251848Z SSMIS 91GHZ IMAGE. THE SSMIS
IMAGE SHOWS A BANDING FEATURE OVER THE NORTHERN SEMICIRCLE WITH AN
EYEWALL SURROUNDING A 50NM DIAMETER MICROWAVE EYE FEATURE, WHICH
SUPPORTS THE INITIAL POSITION WITH GOOD CONFIDENCE. DESPITE THE
RECENT WEAKENING TREND, THE INITIAL INTENSITY IS HELD AT SUPER
TYPHOON STRENGTH (130 KNOTS) BASED ON A PGTW DVORAK CURRENT
INTENSITY ESTIMATE OF 127 KNOTS, CONSISTENT WITH A 251622Z SATCON
ESTIMATE OF 132 KNOTS. STY 31W IS TRACKING WEST-NORTHWESTWARD ALONG
THE SOUTHWEST PERIPHERY OF A DEEP SUBTROPICAL RIDGE (STR) POSITIONED
TO THE NORTHEAST WITH A BREAK IN THE STR LOCATED SOUTH OF HONSHU
(NORTH OF THE SYSTEM) ASSOCIATED WITH A BROAD, WEAK MIDLATITUDE
SHORTWAVE TROUGH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. STY 31W IS FORECAST TO CONTINUE TRACKING WEST-NORTHWESTWARD
TOWARD THE BREAK IN THE STR THROUGH TAU 36, HOWEVER, THE SYSTEM
SHOULD GRADUALLY TURN MORE WESTWARD AFTER TAU 36 AS THE
AFOREMENTIONED SHORTWAVE TROUGH PROPAGATES EASTWARD AND A BROAD
MIDLATITUDE RIDGE TO THE NORTH ALLOWS THE STR TO RE-BUILD. EXCLUDING
THE PRIMARY OUTLIER, COAMPS-TC (CTCX), DYNAMIC MODEL GUIDANCE IS IN
FAIR AGREEMENT THROUGH TAU 72 WITH A 225NM SPREAD IN SOLUTIONS AT
TAU 72. STY 31W IS EXPECTED TO MAINTAIN STY STRENGTH THROUGH TAU 12
AS THE EYEWALL RE-STRENGTHENS AND THE EYE CONTRACTS. HOWEVER, AFTER
TAU 12, THE SYSTEM SHOULD GRADUALLY WEAKEN AS VERTICAL WIND SHEAR
INCREASES.
   C. BEYOND TAU 72, THERE IS INCREASING UNCERTAINTY IN THE FORECAST
TRACK WITH TWO DISTINCT CLUSTERS OF MODEL GUIDANCE. ECMWF, UKMET,
JGSM AND AFUM INDICATE A MORE WESTWARD TRACK OVER LUZON ISLAND.
HWRF, COAMPS-TC, GFS, NAVGEM, EEMN AND AEMN INDICATE A RE-CURVE
SCENARIO WITH SIGNIFICANT DIFFERENCES IN THE RE-CURVE TIMING AND
TRACK SPEEDS AFTER TAU 72. BASED ON ANALYSIS OF MODEL FIELDS FROM
BOTH CLUSTERS, THE RE-CURVE SCENARIO IS ASSESSED AS UNLIKELY DUE TO
A LACK OF A DEEP MIDLATITUDE SHORTWAVE TROUGH AND THE PRESENCE OF A
LOW-LEVEL RIDGE FORECAST TO BUILD OVER THE EAST CHINA SEA. THE JTWC
FORECAST TRACK FAVORS A MORE WESTWARD TRACK WITH A DECREASE IN TRACK
SPEEDS ASSOCIATED WITH A BREAK IN THE STR AND INCREASING
NORTHEASTERLY LOW-LEVEL FLOW FORECAST TO DEVELOP EAST OF TAIWAN.
BASED ON THE BIFURCATION IN THE DYNAMIC MODELS AND LARGE SPREAD,
THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.//
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