WDPN31 PGTW 211500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING 
NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0N 111.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 188 NM EAST-NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 30W (FENGSHEN) IS STILL BEING STEERED BY THE 
SUBTROPICAL RIDGE (STR) TO THE NORTHWEST, WHILE THE CIRCULATION IS 
INTERACTING WITH THE COOLER AND MORE DRY AIR BROUGHT BY THE COLD 
SURGE EVENT OCCURRING ALONG THE COASTLINE OF CHINA. THIS INTERACTION 
CAN BE SEEN VIA ENHANCED CONVECTION AND SLOWING OF THE SYSTEM OVER 
THE PAST 6 HOURS DEPICTED ON ANIMATED ENHANCED INFRARED (EIR) 
SATELLITE IMAGERY. ENVIRONMENTAL CONDITIONS REMAIN MARGINAL WITH 
VERTICAL WIND SHEAR AT 15-20 KTS, SEA SURFACE TEMPERATURES BETWEEN 27 
C AND 28 C, AS WELL AS MODERATE OUTFLOW. A SIGNIFICANT AMOUNT OF DRY 
AIR SURROUNDS THE SYSTEM, SLOWLY BEGINNING TO ENTER THE CORE OF THE 
CIRCULATION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE 
BASED ON THE AGENCY FIXES, AS WELL AS A PARTIALLY EXPOSED LOW-LEVEL 
CIRCULATION CENTER OBSERVED IN THE ANIMATED EIR. THE INITIAL 
INTENSITY IS PLACED WITH HIGH CONFIDENCE BASED ON A PARTIAL 211310Z 
SCATTEROMETER DATA, AS WELL AS OBJECTIVE INTENSITY AIDS LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGING TO THE NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T4.0 - 65 KTS
   DEMS: T3.5 - 55 KTS
   CIMSS ADT: 32 KTS AT 211140Z
   CIMSS AIDT: 33 KTS AT 211140Z
   CIMSS D-MINT: 41 KTS AT 211136Z
   CIMSS D-PRINT: 39 KTS AT 211210Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS FENGSHEN WILL CONTINUE TRACKING WEST-
SOUTHWESTWARD DRIVEN BY THE SUBTROPICAL RIDGE TO THE NORTHWEST. OVER 
THE NEXT 12 HOURS THE STORM IS EXPECTED TO MEET STRONGER RESISTANCE 
FROM THE COLD SURGE TO THE WEST. AROUND TAU 24 THIS INTERACTION WILL 
HAVE SLOWED DOWN AND PUSHED TS FENGSHEN FURTHER SOUTHWEST. THE COOL 
AND DRY AIR OF THE SURGE WILL ALSO CONTINUE TO BE DRAGGED INTO THE 
CIRCULATION, CAUSING WEAKENING AS THE STORM APPROACHES THE COAST OF 
VIETNAM. FOLLOWING THE LANDFALL, TS FENGSHEN WILL PROCEED TO
DISSIPATE AND IS EXPECTED TO WEAKEN BELOW 25 KTS SHORTLY AFTER TAU
48.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE HAS A CROSS-TRACK
SPREAD OF 70 NM AT LANDFALL. THERE ARE STILL A FEW MODELS
STRUGGLING WITH THE SPEED OF THE STORM AS IT APPROACHES LANDFALL,
WITH ECMWF PROJECTING THE FASTEST TRACK AND NAVGEM THE SLOWEST. THE 
JTWC FORECAST IS PLACED CLOSE TO THE CONSENSUS, WITH LANDFALL 
TIMELINE FALLING BETWEEN TAUS 24 AND 36 AND A SLOWER PROGRESSION 
INLAND. INTENSITY GUIDANCE IS ALSO TIGHT, WITH ALL MODELS DEPICTING A
STEADY WEAKENING TREND AFTER TAU 12. THE OFFICIAL JTWC INTENSITY 
FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH 
CONFIDENCE.

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