WDPN31 PGTW 181500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (SANBA) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.6N 108.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 156 NM NORTH OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A
MEDIUM-SIZED, DEVELOPING SYSTEM THAT HAS DRIFTED FROM THE SOUTH
CHINA SEA INTO THE GULF OF TONKIN JUST SOUTHWEST OF HAINAN AND
MAINTAINED FLARING DEEP CONVECTION OVER THE CENTRAL DENSE OVERCAST
(CDO) AND FORMATIVE BANDS WRAPPING TIGHTER FROM THE NORTHEASTERN
PERIPHERY INTO THE CDO THAT IS OBSCURING THE LOW LEVEL CIRCULATION
(LLC). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED
NEAR THE OVERSHOOTING CLOUD TOPS IN THE MIDDLE OF THE CDO AND ON
TOP OF THE AGENCY FIX CLUSTER. THE INITIAL INTENSITY OF 35KTS IS 
ALSO PLACED WITH MEDIUM CONFIDENCE BASED ON THE PGTW, KNES, AND 
DEMS DVORAK INTENSITY ESTIMATES AND REFLECTS THE 6-HR SUSTAINED EIR 
STRUCTURE. ANALYSIS INDICATES A MARGINALLY FAVORABLE ENVIRONMENT 
WITH LOW VWS, WARM SST, AND MODERATE POLEWARD OUTFLOW, TEMPERED BY 
PROXIMITY TO LAND.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
EAST-NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   DEMS: T2.5 - 35 KTS
   CIMSS ADT: 49 KTS AT 181130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS SANBA WILL TRACK MORE NORTH-NORTHWESTWARD
IN THE GULF OF TONKIN ALONG THE WESTERN PERIPHERY OF A RECEDING STR 
TO THE EAST. AFTER TAU 36, A SECONDARY STR APPROACHING FROM THE WEST 
WILL COMPETE FOR STEERING AND FORCE THE CYCLONE IN A QUASI-STATIONARY
(QS) MODE UP TO TAU 72 BEFORE SLOWLY DRIVING IT SOUTHWARD. THE
MARGINALLY FAVORABLE ENVIRONMENT WILL FUEL A MODEST INTENSIFICATION
TO A PEAK 0F 45KTS BY TAU 36. AFTERWARD, LAND INTERFERENCE FROM
NORTHERN VIETNAM TO THE WEST AND HAINAN ISLAND TO THE EAST, SST
COOLING DUE TO CYCLONIC UPWELLING DUE TO THE QS STORM MOTION, THEN
INTRUSION OF COOL DRY AIR FROM CHINA WILL GRADUALLY WEAKEN THE
SYSTEM TO DISSIPATION TAU 72.  


MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT UP
TO TAU 36 THEN DIVERGE SIGNIFICANTLY AFTERWARD AS THE MODELS
DIVERGE ALONG AND ACROSS TRACK DURING THE QS PHASE AND SLOW
SOUTHWARD DRIFT, LENDING OVERALL MEDIUM CONFIDENCE TO THE JTWC
TRACK AND INTENSITY FORECASTS. 


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