Tropical Storm NORU Advisory 9月28日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (NORU) WARNING NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 16.0N 109.0E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 40 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 43 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
SYSTEM THAT IS CONTINUING TO DECREASE IN INTENSITY DUE TO EASTERLY
WIND SHEAR. THE SATELLITE IMAGERY INDICATES THE ONCE PIN HOLE EYE
FEATURE IS NO LONGER EVIDENT AS DEEP CONVECTION WRAPS INTO A DEEP
CONVECTIVE CLOUD STRUCTURE. AN EARLIER 271105Z SSMIS 91GHZ
MICROWAVE IMAGE DEPICTS A SOLID BAND OF DEEP CONVECTION WRAPPING UP
THE EAST SIDE AND A WEAKER BAND ON THE WEST SIDE BUT NO EYEWALL OR
DEEP CONVECTIVE BAND IN THE NORTHERN PERIPHERY. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED EIR
IMAGERY ALONG WITH THE VIETNAMESE RADAR IMAGERY SHOWING THE LOW
LEVEL CIRCULATION CENTER (LLCC). THE INITIAL INTENSITY IS ALSO
PLACED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF SUBJECTIVE DVORAK
INTENSITIES FROM PGTW T5.5, RJTD T5.5, AND KNES T5.5. OBJECTIVE
AUTOMATED DVORAK ESTIMATES INTENSITIES FROM ADT REMAINS ON THE LOW
END, DOWN TO 84 KTS. THEREFORE THE INITIAL INTENSITY IS PLACED CLOSER
TO SUBJECTIVE AGENCY DVORAK ESTIMATES.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) OVER SOUTHERN CHINA
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 84 KTS AT 271740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TY 18W (NORU) CONTINUES TO RAPIDLY WEAKEN OVER
THE PAST 12 HOURS AS ENVIRONMENTAL CONDITIONS ARE MARGINALLY
UNFAVORABLE WITH STRONG VERTICAL WIND SHEAR (VWS) (25-30KTS),
OFFSET BY WARM SEA SURFACE TEMPERATURES (29-30C), AND STRONG
EQUATORWARD OUTFLOW. TY 18W IS FORECASTED TO TRACK WESTWARD THROUGH
OUT THE FORECAST PERIOD UNDER THE STEERING INFLUENCE OF A
DEEP-LAYER SUBTROPICAL RIDGE (STR) OVER SOUTHERN CHINA, BEFORE
MAKING LANDFALL WITHIN THE NEXT 12-18 HOURS INTO CENTRAL VIETNAM
NEAR DA NANG, VIETNAM. AFTER TAU 12, TY 18W WILL CONTINUE TRACKING
WESTWARD WITHIN UNFAVORABLE ENVIRONMENTAL CONDITIONS WHICH WILL
RESULT IN THE SYSTEM CONTINUING TO DECREASE IN INTENSITY DUE TO THE
INFLUENCE OF INCREASING VWS, AS WELL AS TERRAIN INDUCED FRICTIONAL
EFFECTS OF LAND INTERACTION. BY TAU 48, THE SYSTEM TRACKS FURTHER
INLAND OVER SOUTHEAST ASIA WITH DISSIPATION EXPECTED.
MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT REGARDING THE TRACK FORECAST, WITH A GRADUAL SPREAD OF
ONLY 78NM BY TAU 48. THIS LENDS HIGH CONFIDENCE IN THE JTWC TRACK
FORECAST THROUGHOUT THE FORECAST. THE INTENSITY GUIDANCE IS IN
GOOD AGREEMENT THAT THE SYSTEM WILL RAPIDLY WEAKEN THROUGHOUT THE
FORECAST PERIOD. HOWEVER, THE OFFICIAL JTWC FORECAST REMAINS HIGHER
THAN THE MULTI-MODEL CONSENSUS GUIDANCE THROUGH TAU 24 AS IT IS
UNREALISTIC TO SEE 70 KNOTS OF WEAKENING AFTER LANDFALL. THE
OVERALL CONFIDENCE IN THE JTWC INTENSITY FORECAST IS MEDIUM DUE
SOME UNCERTAINTY IN THE INITIAL INTENSITY ALONG WITH HOW QUICKLY
THE SYSTEM WEAKENS THROUGH OUT THE FORECAST PERIOD.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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