WDPN31 PGTW 112100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (CONSON) WARNING NR 
024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.2N 109.1E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 67 NM SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING
DEEP CONVECTION DISPLACED WEST OF AN EXPOSED, WELL-DEFINED LOW-LEVEL 
CIRCULATION CENTER (LLCC). ANIMATED RADAR IMAGERY INDICATES A QUASI-
STATIONARY SYSTEM OVER WATER WITH A WELL-ORGANIZED LLCC AND TIGHTLY-
WRAPPED RAINBANDS. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON EIR AND RADAR IMAGERY. THE INITIAL INTENSITY OF 
40 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PGTW DVORAK 
ESTIMATE AND THE SATCON ESTIMATE. SURFACE OBSERVATIONS ARE LIMITED 
BUT QUANG NGAI, 18NM WSW OF THE CENTER, REPORTED LIGHT WINDS WITH A 
MINIMUM SLP VALUE OF 994.7MB, WHICH CORRESPONDS TO MINIMAL TROPICAL 
STORM STRENGTH (35-40 KNOTS). UPPER-LEVEL CONDITIONS ARE MARGINAL 
WITH STRONG (25 KNOTS) EASTERLY VERTICAL WIND SHEAR (VWS) AND 
DIFFLUENT FLOW ALOFT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A
WEAK SUBTROPICAL RIDGE (STR) TO THE NORTH AND A NEAR-EQUATORIAL
RIDGE (NER) TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   CIMSS SATCON: 39 KTS AT 111420Z
   CIMSS ADT: 32 KTS AT 111740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: NO MAJOR CHANGES BUT THIS FORECAST
TRACK INCORPORATES A MORE QUASI-STATIONARY TRACK MOTION OVER WATER
THROUGH TAU 24.

FORECAST DISCUSSION: TS 18W IS FORECAST TO MAINTAIN A
QUASI-STATIONARY MOTION THROUGH TAU 24 UNDER A COMPETING STEERING
ENVIRONMENT. AFTER TAU 24, THE STR TO THE NORTH IS EXPECTED TO
STRENGTHEN, ALLOWING TS 18W TO ACCELERATE WEST-NORTHWESTWARD INTO
VIETNAM. ONCE THE SYSTEM TRACKS OVER THE MOUNTAINOUS TERRAIN OF
VIETNAM, IT'S EXPECTED TO RAPIDLY DISSIPATE.

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, THE BULK OF THE
MODEL GUIDANCE SUPPORTS THE SHORT DURATION QUASI-STATIONARY TRACK
MOTION THEN AN ACCELERATED TRACK NORTHWESTWARD TO WEST-NORTHWESTWARD 
AFTER TAU 24. HOWEVER, DUE TO THE UNCERTAINTY IN THE EXACT TRACK, 
THERE IS MEDIUM CONFIDENCE IN THE JTWC FORECAST TRACK. THE JTWC 
INTENSITY FORECAST IS OBVIOUSLY LINKED TO THE TIMING OF THE 
LANDFALL, WHICH IS EXPECTED NEAR TAU 24 WITH DISSIPATION EXPECTED BY 
TAU 48.    

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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