WDPN31 PGTW 220900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING 
NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.5N 110.3E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 146 NM NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 30W (FENGSHEN) HAS BEEN ON A WARMING TREND,
WHILE EXHIBITING LESS ORGANIZED STRUCTURE OVER THE PAST 6 HOURS, AS
OBSERVED VIA ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY.
INTERACTION WITH COOL, DRY AIR FROM THE WEST HAS SLOWED THE SYSTEM
AS IT CONTINUES TO TRACK WEST. THE CENTER OF THE CIRCULATION HAS
BECOME DISPLACED FROM THE MAJORITY OF ASSOCIATED CONVECTIVE
ACTIVITY TO THE NORTH DUE TO PERSISTENT SOUTHERLY VERTICAL WIND
SHEAR (VWS). ADDITIONALLY, UPWELLING EFFECTS AND ASSOCIATED SEA
SURFACE TEMPERATURE DECREASE CONTRIBUTE TO AN OVERALL WEAKENING
TREND. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
A 220250Z METOP-C ASCAT DATA. THE INITIAL INTENSITY OF 45 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED ASCAT
PASS, IN CONJUNCTION WITH THE OBJECTIVE INTENSITY AIDS LISTED
BELOW.

INITIAL WIND RADII BASIS: 220250Z METOP-C ASCAT SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T4.0 - 65 KTS
   DEMS: T3.5 - 55 KTS
   CIMSS SATCON: 43 KTS AT 220609Z
   CIMSS ADT: 39 KTS AT 220540Z
   CIMSS AIDT: 36 KTS AT 220730Z
   CIMSS D-MINT: 48 KTS AT 220609Z
   CIMSS D-PRINT: 38 KTS AT 220730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 FENGSHEN IS FORECAST TO CONTINUE TRACKING
WEST-SOUTHWESTWARD UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE TO
THE NORTHWEST FOR THE REMAINDER OF THE FORECAST PERIOD, WHILE
CONTINUING TO WEAKEN AND BECOMING MORE DISORGANIZED AS COOL, DRY
AIR IS CONTINUOUSLY PUMPED INTO THE SYSTEM. THE SYSTEM WILL APPROACH
THE COAST OF VIETNAM AS A WEAK TROPICAL DEPRESSION AROUND TAU 24.
TS FENGSHEN IS EXPECTED TO FULLY DISSIPATE OVER LAND BY TAU 48.

MODEL DISCUSSION: MODEL GUIDANCE DEPICTS A CROSS TRACK SPREAD OF 60
NM AT TAU 24, WITH THE SPREAD ENVELOPE INCREASING TO AROUND 85 NM
FOR THE REMAINDER OF THE FORECAST PERIOD. THE JTWC OFFICIAL TRACK
IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE SPREAD IS BETWEEN 5-10 KTS WITH HIGHER END OF
THAT SPREAD DEPICTED AFTER TAU 24 DUE TO THE EFFECTS OF LAND
INTERACTION. THE 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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