WDPN31 PGTW 212100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (WIPHA) WARNING NR 
014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.8N 107.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 96 NM EAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SYMMETRIC 
CENTRAL DENSE OVERCAST FEATURE OBSCURING THE LOW-LEVEL CIRCULATION. 
HOWEVER, ANIMATED RADAR IMAGERY REVEALS CURVED CONVECTIVE BANDING 
WRAPPING INTO A RAGGED, DEFINED CENTER. SEVERAL SURFACE OBSERVATIONS 
FROM AROUND THE PERIPHERY OF THE SYSTEM TRIANGULATE AND SUPPORT THE 
INITIAL POSITION ASSESSMENT WITH MEDIUM CONFIDENCE. ENVIRONMENTAL 
CONDITIONS ARE MARGINAL, WITH FRICTIONAL EFFECTS DUE TO LAND 
INTERACTION AND PERSISTENT NORTHEASTERLY VERTICAL WIND SHEAR OF 30-35 
KNOTS OFFSET BY MODERATE EQUATORWARD OUTFLOW AND WARM (30C) SST 
VALUES. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON THE AGENCY DVORAK ESTIMATES AND CIMSS OBJECTIVE 
ESTIMATES, WHICH RANGE FROM 45 TO 55 KNOTS. ADDITIONALLY, SURFACE 
OBSERVATIONS FROM BACH LONG VI (48839), 42NM SOUTH-SOUTHEAST OF THE 
CENTER, INDICATE SOUTHWESTERLY WINDS AT 43 KNOTS, WITH SLP NEAR 985MB.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
POSITIONED TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 54 KTS AT 211740Z
   CIMSS ADT: 51 KTS AT 211800Z
   CIMSS AIDT: 46 KTS AT 211800Z
   CIMSS D-MINT: 45 KTS AT 211800Z
   CIMSS D-PRINT: 45 KTS AT 211800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 30+ KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: INTERACTION WITH LAND

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: TROPICAL STORM (TS) 09W IS TRACKING SLOWLY
WEST-SOUTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL
RIDGE AND IS FORECAST TO MAKE LANDFALL IN ABOUT 06-09 HOURS. AFTER
MAKING LANDFALL, THE SYSTEM WILL TRACK INLAND ON A WESTWARD
TRAJECTORY AND DISSIPATE RAPIDLY BY TAU 36.   

MODEL DISCUSSION: DETERMINISTIC GUIDANCE REMAINS IN GOOD AGREEMENT,
WITH A 40-45NM CROSS-TRACK SPREAD FROM TAU 24 TO TAU 36. THE
211200Z GEFS AND ECENS RUNS SUPPORT THE JTWC TRACK FORECAST BUT
INDICATE A WIDER SPREAD OF SOLUTIONS. THEREFORE, THERE IS MEDIUM
CONFIDENCE IN THE JTWC TRACK FORECAST. RELIABLE INTENSITY GUIDANCE
IS IN GOOD AGREEMENT SUPPORTING THE STEADY WEAKENING TREND AS THE
SYSTEM TRACKS INLAND.  

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