WDPN31 PGTW 281500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.3N 115.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 389 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A BROAD
LOW-LEVEL CIRCULATION WITH MULTIPLE MESOVORTICES ROTATING 
CYCLONICALLY AROUND AN EXPOSED CENTROID. THE CONVECTIVE STRUCTURE
HAS DEGRADED OVER THE PAST SIX HOURS AS INDICATED IN THE 281026Z
SSMIS 91GHZ COLOR COMPOSITE MICROWAVE IMAGE, WITH FRAGMENTED
CONVECTIVE BANDING AND A WEAKLY DEFINED LOW-LEVEL CIRCULATION
CENTER. A 281347Z ASCAT-B IMAGE REVEALS A DEFINED CIRCULATION, WITH
25-30 KNOT WINDS, WHICH SUPPORTS THE INITIAL POSITION AND INITIAL
INTENSITY WITH MEDIUM CONFIDENCE. ENVIRONMENTAL CONDITIONS REMAIN
MARGINALLY FAVORABLE WITH MODERATE VERTICAL WIND SHEAR OFFSET BY
WESTWARD OUTFLOW AND WARM SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
ENTRENCHED TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS ADT: 30 KTS AT 281130Z
   CIMSS AIDT: 31 KTS AT 281130Z
   CIMSS D-MINT: 23 KTS AT 281028Z
   CIMSS D-PRINT: 22 KTS AT 281330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 20W WILL TRACK WEST-
NORTHWESTWARD THROUGH TAU 36 ALONG THE SOUTHWESTERN PERIPHERY OF THE 
STR WITH SLOW INTENSIFICATION DUE TO THE MARGINALLY FAVORABLE 
CONDITIONS, BROAD NATURE OF THE LLCC, AND LACK OF A VERTICALLY 
ALIGNED VORTEX. PEAK INTENSITY IS EXPECTED TO REMAIN IN THE 40-45 
KNOT RANGE AT BEST. AFTER TAU 36, THE SYSTEM WILL ENCOUNTER 
INCREASING NORTHEASTERLIES AND INCREASING VERTICAL WIND SHEAR, WHICH 
WILL LEAD TO A STEADY WEAKENING TREND. AFTER LANDFALL NEAR TAU 48, 
THE SYSTEM WILL WEAKEN RAPIDLY AND DISSIPATE NO LATER THAN TAU 72. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN TIGHT AGREEMENT, 
WITH A 60NM CROSS-TRACK SPREAD AT TAU 48. THE 280600Z GEFS AND 
280000Z ECENS ENSEMBLES ARE ALSO IN GOOD AGREEMENT LENDING HIGH 
CONFIDENCE TO THE JTWC TRACK FORECAST. RELIABLE INTENSITY GUIDANCE TO 
INCLUDE HAFS-A, COAMPS-TC (GFS) AND HWRF ARE IN FAIR AGREEMENT, WITH 
A PEAK INTENSITY RANGING FROM 31 TO 45 KNOTS FROM TAU 24 TO TAU 36. 

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