WDPN34 PGTW 150900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (USAGI) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.1N 119.6E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 262 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
DETERIORATING LOW-LEVEL CIRCULATION, WITH DEEP CONVECTION FLARING
TO THE NORTHEAST OF A BROAD, PARTIALLY-EXPOSED CENTER. MSI ALSO
SHOWS EXTENSIVE STRATOCUMULUS ADVECTING SOUTHWARD THROUGH THE
TAIWAN STRAIT INTO THE SOUTHWESTERN QUADRANT OF THE SYSTEM. THIS
COOLER, MORE STABLE AND DRIER AIR IS SERVING TO RAPIDLY WEAKEN THE
SYSTEM. ANIMATED RADAR IMAGERY ALSO REVEALS A RAPIDLY WEAKENING
SYSTEM WITH FRAGMENTED CONVECTIVE BANDING OVER THE EASTERN
SEMICIRCLE. A 150458Z AMSR2 89GHZ COLOR COMPOSITE MICROWAVE IMAGE
SUPPORTS THE INITIAL POSITION WITH MEDIUM CONFIDENCE AND SHOWS A
DEFINED BUT ELONGATED LOW-LEVEL CIRCULATION CENTER WITH FRAGMENTED
BANDING DISPLACED OVER THE EASTERN SEMICIRCLE DUE TO WESTERLY
VERTICAL WIND SHEAR IN ADDITION TO THE DRY AIR ENTRAINMENT. THE
INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON A 150458Z AMSR2 WINDSPEED IMAGE, WHICH SHOWS A BROAD WIND
MINIMUM WITH A SWATH OF 45-50 KNOT WINDS OVER THE EASTERN SEMICIRCLE. 
AGENCY SUBJECTIVE DVORAK DATA-T ESTIMATES HAVE DECREASED QUICKLY AND 
RANGE FROM 45-55 KNOTS. DUE TO THE RAPID WEAKENING AND DVORAK 
CONSTRAINTS, THE CURRENT INTENSITY ESTIMATES (SEE BELOW) ARE ASSESSED 
AS TOO HIGH ALTHOUGH BOTH RJTD AND RCTP HAVE BROKEN CONSTRAINTS. 

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: T4.5 - 77 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   CIMSS SATCON: 71 KTS AT 150229Z
   CIMSS ADT: 87 KTS AT 150530Z
   CIMSS AIDT: 70 KTS AT 150730Z
   CIMSS D-MINT: 35 KTS AT 150732Z
   CIMSS D-PRINT: 36 KTS AT 150730Z

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: MEDIUM

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 18. AFTER TAU 18, 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 (ECMF, UEMI, EEMI, AVNI, JGSI) OF AIDS
TRACKING THE SYSTEM NORTHWARD TO NORTHEASTWARD OVER NORTHERN TAIWAN
AND ISHIGAKI-JIMA AND ANOTHER CLUSTER (NVGI, AEMI) TURNING THE
SYSTEM SOUTHWESTWARD. THE 150000Z EPS ENSEMBLE HAS TRENDED
CONSISTENTLY AWAY FROM THE RECURVE SCENARIO WITH ONLY TWO SOLUTIONS
TRACKING THE SYSTEM OVER OKINAWA. THE BULK OF THE EPS SOLUTIONS NOW
INDICATE DISSIPATION NEAR TAIWAIN 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: MEDIUM//
NNNN