WDPN31 PGTW 220300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING NR 
017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.2N 111.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 214 NM EAST-NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 30W WITH A DEVELOPING A DRY SLOT, THOUGH THE CORE OF THE
SYSTEM REMAINS MOIST WITH PERSISTENT CONVECTION ALONG THE WESTERN
PERIPHERY. A 212310Z F17 91GHZ SSMIS PASS REVEALS THAT TROPICAL
STORM (TS) 30W HAS REMAINED QUASI-STATIONARY FOR THE PAST 12 HOURS,
AND THAT THE UPPER-LEVEL CENTER CONTINUES TO BE DISPLACED TO THE
WEST OF THE LOWER-LEVEL CENTER. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE AFOREMENTIONED F17 91GHZ MICROWAVE
IMAGE. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON THE OBJECTIVE 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: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 45 KTS AT 212300Z
   CIMSS ADT: 39 KTS AT 220030Z
   CIMSS AIDT: 36 KTS AT 220030Z
   CIMSS D-MINT: 42 KTS AT 212311Z
   CIMSS D-PRINT: 46 KTS AT 220030Z

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: TS 30W HAS REMAINED QUASI-STATIONARY OVER THE 
PAST 6 HOURS, BUT IS FORECAST TO PICK UP SLIGHT SPEED AS IT TRACKS 
FARTHER WEST-SOUTHWESTWARD. 30W WILL MAINTAIN A WEST-SOUTHWESTWARD 
TRAJECTORY THROUGH LANDFALL NEAR DA NANG, VIETNAM BEFORE TAU 36. THE 
ENVIRONMENT IN THE SOUTH CHINA SEA WILL BECOME INCREASINGLY 
INHOSPITABLE OVER THE NEXT 24 HOURS DUE TO THE DRIER AIR ADVECTION 
SOUTHWESTWARD BY THE COLD SURGE AND INCREASING VERTICAL WIND SHEAR. AS 
A RESULT OF THE WORSENING ENVIRONMENT, 30W WILL QUICKLY WEAKEN TO A 
WEAK TROPICAL DEPRESSION AT LANDFALL, WITH DISSIPATION EXPECTED 
IMMINENTLY AFTER LANDFALL.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THAT 30W WILL TRACK WEST-SOUTHWESTWARD FOR THE DURATION OF
THE FORECAST PERIOD. HOWEVER, SOME MODELS DISAGREE ON TRACK SPEED 
WHILE 30W IS OVER LAND, RESULTING IN A SIGNIFICANT ALONG-TRACK SPREAD 
BETWEEN TAU 36-48. DUE TO THE ALONG-TRACK SPREAD IN GUIDANCE, THE JTWC 
TRACK FORECAST LIES WITH THE BULK OF CONSENSUS MEMBERS WITH OVERALL 
MEDIUM CONFIDENCE. JTWC INTENSITY GUIDANCE IS IN STRONG AGREEMENT THAT 
30W WILL QUICKLY DISSIPATE, WITH ALL MODELS SIGNALING DISSIPATION 
BETWEEN TAU 36-48. 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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