WDPN31 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.5N 108.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 38 NM NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 30W AS A SHALLOW AND PARTIALLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC) WITH LIMITED REMAINING CONVECTION. 30W
REMAINS UNDER HIGH SOUTHWESTERLY SHEAR, INDICATED BY UPPER-LEVEL
CLOUDS MOVING IN STRAIGHT-LINE FLOW OVER THE SYSTEM. THE DRIER AIR
ASSOCIATED WITH THE SOUTHWESTWARD COLD SURGE HAS ENTRAINED INTO THE
CORE, FURTHER WEAKENING THE SYSTEM OVER THE PAST 6 HOURS. AS THE
MID- AND UPPER-LEVELS OF THE STORM'S STRUCTURE HAS ERODED, 30W
HAS GAINED SPEED OF APPROACH OVER WATER, INFLUENCED BY BOTH THE 
STEERING RIDGE AND THE AFOREMENTIONED COLD SURGE. THE INITIAL POSITION 
IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC 
IN ANIMATED EIR. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE AUTOMATED OBJECTIVE INTENSITY ESTIMATES AND 
AGENCY DVORAK FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) TO THE NORTH
AND NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   CIMSS SATCON: 39 KTS AT 221830Z
   CIMSS ADT: 28 KTS AT 221830Z
   CIMSS AIDT: 30 KTS AT 221830Z
   CIMSS D-PRINT: 33 KTS AT 221830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 30W (FENGSHEN) WILL CONTINUE ITS
SOUTHWESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD.
DRY AIR ENTRAINING INTO THE CORE AND HIGH (20-25 KTS) SOUTHWESTERLY
VERTICAL WIND SHEAR WILL EXPEDITE FENGSHEN'S TERMINAL WEAKENING
PRIOR TO LANDFALL. LANDFALL IS ANTICIPATED NO LATER THAN TAU 12
NEAR DA NANG, VIETNAM, WITH DISSIPATION FORECASTED OVER LAND NO LATER
THAN TAU 36.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT IN 30W MAKING LANDFALL PRIOR TO TAU 12. AFTER LANDFALL,
HOWEVER, MODELS DISAGREE ABOUT THE STORM'S MOTION WHILE OVER LAND,
INTRODUCING UNCERTAINTY IN BOTH THE ALONG-TRACK SPEED AND CROSS-TRACK
DIRECTION. THE JTWC TRACK FORECAST IS PLACED IN LINE WITH THE
MULTI-MODEL CONSENSUS WITH OVERALL MEDIUM CONFIDENCE. RELIABLE
INTENSITY GUIDANCE IS IN STRONG AGREEMENT THAT 30W WILL QUICKLY
WEAKEN, WITH ALL MODELS PREDICTING DISSIPATION NO LATER THAT TAU
36. AS A RESULT, THE JTWC INTENSITY GUIDANCE IS PLACED WITH HIGH
CONFIDENCE.

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