WDPN31 PGTW 120300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (CONSON) 
WARNING NR 025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.4N 109.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 59 NM SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 15 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 30 KTS IS ASSESSED WITH HIGH CONFIDENCE HEDGED JUST 
BELOW THE PGTW DVORAK ESTIMATE DUE TO THE WEAK CONVECTIVE STRUCTURE. 
UPPER-LEVEL CONDITIONS ARE MARGINAL WITH STRONG (25 KNOTS) EASTERLY 
VERTICAL WIND SHEAR (VWS) AND DIFFLUENT FLOW ALOFT.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

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: T2.5 - 35 KTS
   CIMSS ADT: 43 KTS AT 112340Z

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: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TD 18W IS FORECAST TO MAINTAIN A
QUASI-STATIONARY MOTION THROUGH TAU 12 UNDER A COMPETING STEERING
ENVIRONMENT. AFTER TAU 12, THE STR TO THE NORTH IS EXPECTED TO
STRENGTHEN, ALLOWING TD 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 12. 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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