WDPN31 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.3N 117.5E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 535 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
CONSOLIDATING SYSTEM WITH BUILDING CONVECTION ALONG THE EASTERN
SEMICIRCLE AND IMPROVING RADIAL OUTFLOW. A 191648Z 37GHZ GMI
MICROWAVE IMAGE REVEALS THE LOWER LEVELS HAVE CONSIDERABLY
CONSOLIDATED OVER THE PAST 6 HOURS AS THE STORM HAS MOVED AWAY FROM 
LAND. ENVIRONMENTAL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT, 
CHARACTERIZED BY LOW (10-15 KTS) VERTICAL WIND SHEAR, VERY WARM (28-29 
C) SEA SURFACE TEMPERATURES, AND GOOD DIVERGENCE ALOFT. THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED 
GMI MICROWAVE DATA. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH 
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND THE CIMSS 
AUTOMATED OBJECTIVE INTENSITY ESTIMATES LISTED BELOW, CORROBORATED BY 
THE IMPROVED APPEARANCE IN BOTH ANIMATED MSI AND THE GMI MICROWAVE 
IMAGE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 40 KTS AT 191940Z
   CIMSS ADT: 35 KTS AT 191940Z
   CIMSS AIDT: 35 KTS AT 191940Z
   CIMSS D-MINT: 36 KTS AT 191756Z
   CIMSS D-PRINT: 31 KTS AT 191940Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 30W (FENGSHEN) WILL
CONTINUE WEST-NORTHWESTWARD FOR THE NEXT 24 HOURS WHILE IT REMAINS
UNDER THE STEERING INFLUENCE OF THE STR TO ITS NORTHEAST. AROUND
TAU 24, 30W WILL ENTER INTO A COMPETING STEERING ENVIRONMENT AS IT
ENCOUNTERS A RIDGE BUILDING OVER SOUTHEAST ASIA. FENGSHEN WILL
TRANSITION STEERING RIDGES AT THAT POINT, CURVE SOUTHWESTWARD, AND
TRACK SOUTHWESTWARD FOR THE REMAINDER OF THE FORECAST PERIOD.
LEADING UP TO TAU 36, THE SOUTH CHINA SEA IS AN OVERALL FAVORABLE
ENVIRONMENT FOR DEVELOPMENT, ALLOWING 30W TO INTENSIFY STEADILY TO
A PEAK OF 65KTS AT TAU 36. BETWEEN TAU 12-36, FENGSHEN WILL COLLIDE
WITH A COLD SURGE FUNNELING SOUTHWESTWARD THROUGH THE TAIWAN
STRAIT, INTRODUCING DRY AIR AND TEMPORARILY EXPANDING THE GALE FORCE 
WINDS ALONG THE NORTHEASTERN PERIPHERY. AFTER TAU 36, SIGNIFICANT DRY 
AIR ENTRAINMENT IN THE MID- TO UPPER-LEVELS WILL STIFLE DEVELOPMENT 
AND BEGIN WEAKENING 30W. 30W WILL CONTINUE TO WEAKEN AS IT TRACKS 
SOUTHWESTWARD, MAKING LANDFALL AROUND DA NANG, VIETNAM AS A WEAK 
TROPICAL STORM AFTER TAU 72, AND DISSIPATING OVERLAND AROUND TAU 96.

MODEL DISCUSSION: DETERMINISTIC TRACK MODELS ARE IN GOOD AGREEMENT
IN A WEST-NORTHWESTWARD TRACK FOR THE FIRST 24 HOURS OF THE
FORECAST. THE MODEL GUIDANCE DIVERGES AFTERWARDS, WITH DIFFERENCES
IN TIMING AND SPEED OF THE SOUTHWESTWARD CURVE AND SUBSEQUENT
FORECAST, RESULTING IN A 200NM CROSS-TRACK SPREAD AT TAU 96 AND A
400NM ALONG-TRACK SPREAD AT THE SAME TIME. THE JTWC TRACK FORECAST
IS PLACED WITH MEDIUM CONFIDENCE FROM TAU 0-72, AND LOW CONFIDENCE
FROM TAU 72-96. RELIABLE INTENSITY GUIDANCE IS IN GOOD AGREEMENT
THAT 30W WILL STEADILY INTENSIFY THROUGH TAU 36 AND PEAK AROUND TAU
36-48. THE 191200Z COAMPS-TC (GFS BOUNDARY CONDITIONS) INTENSITY 
ENSEMBLE INDICATES 70-90 PERCENT PROBABILITY OF MODERATE 
INTENSIFICATION THROUGH TAU 36, WHICH SUPPORTS THE JTWC INTENSITY 
FORECAST. THE JTWC INTENSITY FORECAST LIES HIGHER THAN THE BULK OF
MULTI-MODEL CONSENSUS MEMBERS, BUT IN CONCURRENCE WITH THE COAMPS-TC 
INTENSITY ENSEMBLE, WITH OVERALL MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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