WDPN31 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING 
NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.1N 111.6E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 201 NM EAST-NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 30W (FENGSHEN) CONTINUING TO TRACK SOUTHWESTWARD WITH
LITTLE CHANGE TO THE STRUCTURE OF THE SYSTEM. PERSISTENT DEEP
CONVECTION CONTINUES IN ALL QUADRANTS OF THE CIRCULATION. 
ENVIRONMENTAL CONDITIONS ARE MARGINAL WITH VERTICAL WIND SHEAR OF
15-20 KTS, SEA SURFACE TEMPERATURES OF 27C-28C, AND A SIGNIFICANT
AMOUNT OF DRY AIR AROUND THE SYSTEM, ALTHOUGH NOT YET WRAPPED INTO
THE SYSTEM. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON ANIMATED EIR AND THE AGENCY DVORAK FIXES. THE INITIAL
INTENSITY IS PLACED WITH MEDIUM CONFIDENCE AS AVAILABLE SCATTEROMETER 
DATA HAS ONLY BEEN ABLE TO CAPTURE HALF OF THE SYSTEM ACCURATELY.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGING TO THE NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS SATCON: 46 KTS AT 210538Z
   CIMSS ADT: 39 KTS AT 210530Z
   CIMSS AIDT: 37 KTS AT 210530Z
   CIMSS D-MINT: 35 KTS AT 210540Z
   CIMSS D-PRINT: 36 KTS AT 210700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: INTERACTION WITH COLD SURGE FLOW OVER THE
NORTHWESTERN SOUTH CHINA SEA

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 30W CONTINUES TO BE DRIVEN BY SUBTROPICAL
RIDGING TO THE NORTHWEST. INTERACTION WITH THE COLD SURGE WILL
CONTINUE TO AID CONVECTIVE ACTIVITY AND POLEWARD OUTFLOW IN THE
NEAR TERM. AS IT CONTINUES TO TRACK WEST, THE SYSTEM WILL BE
FURTHER INHIBITED BY VERTICAL WIND SHEAR AND DRY AIR BEING ENTRAINED 
INTO THE CIRCULATION. TS FENGSHEN IS EXPECTED HAVE A SLOW WEAKENING 
TREND AS IT NEARS THE COAST OF VIETNAM AFTER TAU 24 AND IS EXPECTED 
TO FULLY DISSIPATE OVER LAND BY TAU 72. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT, WITH CROSS-TRACK SPREAD OF 75 NM AT LANDFALL.
ALONG-TRACK SPREAD SHOWS A BIT OF UNCERTAINTY IN REGARD TO THE
SPEED OF TC FENGSHEN, WITH ECMWF PROJECTING THE FASTEST TRACK
TOWARD LANDFALL. THE JTWC FORECAST IS PLACED CLOSE TO THE CONSENSUS
WITH LANDFALL BETWEEN TAUS 24 AND 36. THERE IS A TIGHT CONSENSUS
REGARDING INTENSITY AMONG THE MODELS THROUGHOUT THE FORECAST, WITH
ALL MODELS DEPICTING STEADY WEAKENING TREND AFTER TAU 12, WITH SOME
SLIGHT INTENSIFICATION POSSIBLE JUST PRIOR TO THAT. THE OFFICIAL
JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE MULTI-MODEL
CONSENSUS WITH MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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