WDPN31 PGTW 212100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.3N 111.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 216 NM EAST-NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH STRONG
CONVECTION OVER THE NORTHERN AND WESTERN QUADRANTS. ROBUST POLEWARD 
OUTFLOW IS STRENGTHENED BY THE MIDLATITUDE WESTERLIES TO THE NORTH, 
ACCOMPANIED BY SURROUNDING UPPER-LEVEL STRIATIONS. A 211656Z GPM 37 
GHZ 
GMI MICROWAVE IMAGE REVEALS THE LOW-LEVEL CENTER IS COMPACT BUT 
SLIGHTLY ELONGATED ALONG THE EAST-WEST AXIS. 89 GHZ GMI MICROWAVE 
IMAGERY FROM THE SAME GPM PASS REVEALS THAT THE UPPER-LEVEL CENTER IS 
DISPLACED APPROXIMATELY 50NM WEST OF THE LOW-LEVEL CENTER. 
ENVIRONMENTAL ANALYSIS INDICATES A MARGINAL ENVIRONMENT CHARACTERIZED 
BY WARM (28-29 C) SEA SURFACE TEMPERATURES, MODERATE TO HIGH (15-20 
KTS) SOUTHWESTERLY VERTICAL WIND SHEAR, STRONG OUTFLOW ALOFT, AND 
SIGNIFICANT DRY AIR ENTRAINMENT. THE INITIAL POSITION IS PLACED WITH 
HIGH CONFIDENCE BASED ON THE AFOREMENTIONED 37 GHZ GMI IMAGE. THE 
INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED 
ON THE AUTOMATED CIMSS INTENSITY ESTIMATES AND AGENCY DVORAK FIXES 
LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 45 KTS AT 211830Z
   CIMSS ADT: 31 KTS AT 211830Z
   CIMSS AIDT: 35 KTS AT 211830Z
   CIMSS D-MINT: 41 KTS AT 211810Z
   CIMSS D-PRINT: 43 KTS AT 211830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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: TROPICAL STORM (TS) 30W IS FORECAST TO SLOWLY
TRACK WEST-SOUTHWESTWARD FOR THE DURATION OF THE FORECAST PERIOD
WHILE IT REMAINS UNDER THE STEERING INFLUENCE OF THE STR TO ITS
NORTHWEST. THE ENVIRONMENT IN THE SOUTH CHINA SEA IS EXPECTED TO
BECOME MORE HOSTILE OVER THE NEXT 36 HOURS, AS DRIER AIR ASSOCIATED 
WITH THE COLD SURGE AND INCREASING VERTICAL WIND SHEAR SUFFOCATE THE
SYSTEM. AS A RESULT, 30W WILL WEAKEN STEADILY, MAKING LANDFALL
SOUTH OF DA NANG, VIETNAM AS A TROPICAL DEPRESSION BEFORE
DISSIPATING OVER LAND NO LATER THAN TAU 48. 

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THAT 30W WILL TRACK WEST-SOUTHWEST FOR THE DURATION OF
THE FORECAST PERIOD. THERE IS SOME DISAGREEMENT ON TRACK SPEED,
RESULTING IN A 365NM ALONG-TRACK SPREAD AT TAU 48. CROSS-TRACK
SPREAD, HOWEVER, FARES MUCH BETTER, WITH ONLY A 75NM SPREAD AT THE
WIDEST POINT. THE JTWC TRACK FORECAST IS PLACED IN CONCURRENCE WITH
THE BULK OF CONSENSUS MEMBERS WITH OVERALL MEDIUM CONFIDENCE. JTWC
INTENSITY GUIDANCE IS IN STRONG AGREEMENT THAT 30W WILL QUICKLY
DISSIPATE, WITH ALL RELIABLE MODELS PREDICTING DISSIPATION BEFORE
TAU 48. AS A RESULT, THE JTWC INTENSITY FORECAST IS PLACED WITH
HIGH CONFIDENCE.

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