WDPN34 PGTW 151500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (USAGI) WARNING NR 
019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.5N 119.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 240 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A RAPIDLY
DETERIORATING LOW-LEVEL CIRCULATION, WITH DISORGANIZED DEEP 
CONVECTION FLARING TO THE NORTHEAST OF A BROAD, PARTIALLY-EXPOSED 
CENTER. EIR IMAGERY ALSO SHOWS EXTENSIVE STRATOCUMULUS ADVECTING 
SOUTHWARD THROUGH THE TAIWAN STRAIT INTO THE SOUTHWESTERN QUADRANT OF 
THE SYSTEM. THIS SURGE OF COOLER, MORE STABLE AND DRIER AIR IS 
SERVING TO RAPIDLY WEAKEN THE SYSTEM. ANIMATED RADAR IMAGERY SUGGESTS 
A BROAD CENTER DRIFTING POLEWARD, WITH CURVED CONVECTIVE BANDING OVER 
THE NORTHERN SEMICIRCLE. A 150957Z SSMIS 37GHZ MICROWAVE IMAGE 
REVEALS A DEFINED CENTER WITH LIMITED SHALLOW BANDING WRAPPING AROUND 
THE NORTHERN HALF OF THE SYSTEM DUE TO STRONG VERTICAL WIND SHEAR AND 
DRY AIR ENTRAINMENT. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH 
MEDIUM CONFIDENCE BASED ON THE RJTD AND KNES DVORAK ESTIMATES, WHICH 
ARE CONSISTENT WITH THE DEGRADED STRUCTURE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) 
POSITIONED TO THE EAST, WITH WEAK EXTENSION TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T4.5 - 77 KTS
   CIMSS SATCON: 65 KTS AT 151039Z
   CIMSS ADT: 72 KTS AT 150830Z
   CIMSS AIDT: 66 KTS AT 150830Z
   CIMSS D-MINT: 29 KTS AT 150957Z
   CIMSS D-PRINT: 33 KTS AT 151100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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) 27W IS FORECAST TO TRACK
POLEWARD ALONG THE WESTERN PERIPHERY OF THE STR, MAKING LANDFALL
OVER SOUTHERN TAIWAN NEAR TAU 12. AFTER TAU 12, THE SYSTEM WILL TRACK
OVER THE MOUNTAINOUS TERRAIN OF TAIWAN, WITH RAPID WEAKENING AND 
DISSIPATION EXPECTED BY TAU 48. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE CONTINUES TO SHOW A
BIFURCATION WITH ONE CLUSTER (ECMI, UEMI, EEMI, AVNI, JGSI) OF
AIDS TRACKING THE SYSTEM NORTHWARD TO NORTHEASTWARD OVER NORTHERN
TAIWAN AND ISHIGAKI-JIMA AND ANOTHER CLUSTER (NVGI, AFUI) TURNING THE
SYSTEM SOUTHWESTWARD. THE 150600Z EPS ENSEMBLE HAS TRENDED 
CONSISTENTLY AWAY FROM THE RECURVE SCENARIO WITH ONLY THREE SOLUTIONS 
TRACKING THE SYSTEM OVER OKINAWA. THE BULK OF THE EPS SOLUTIONS
NOW INDICATE DISSIPATION NEAR TAIWAN OR SOUTH OF TAIWAN. THE 150000Z
GEFS ENSEMBLE SHOWS NO RECURVE SOLUTIONS, WITH DISSIPATION NEAR
TAIWAN OR SOUTH OF TAIWAN.   

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: HIGH//
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