WDPN31 PGTW 282100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.6N 114.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 336 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL DEPRESSION (TD) 20W HAS MAINTAINED INTENSITY WHILE
TRACKING WEST-NORTHWESTWARD OVER THE PAST SIX HOURS. ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS PATCHY, CYCLING
DEEP CONVECTION OVER THE WESTERN PERIPHERY OF A BROAD AND PARTIALLY
EXPOSED LOW-LEVEL CIRCULATION EVIDENT IN A 281913Z GMI PASS.
DESPITE THE LACK OF INTENSIFICATION, THE GMI DATA INDICATE THAT THE
LOW-LEVEL CIRCULATION HAS CONSOLIDATED SLIGHTLY AROUND A DISTINCT 
CENTER. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED 
ON POSITION FIX DATA FROM PGTW, KNES, AND RJTD AND FURTHER SUPPORTED
BY THE 281913Z GMI PASS. THE INITIAL INTENSITY OF 30 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A CONSENSUS OF AVAILABLE
SUBJECTIVE DVORAK AND AUTOMATED FIX ESTIMATES LISTED BELOW.

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

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS SATCON: 31 KTS AT 281850Z
   CIMSS ADT: 35 KTS AT 281730Z
   CIMSS AIDT: 33 KTS AT 281730Z
   CIMSS D-MINT: 25 KTS AT 281913Z
   CIMSS D-PRINT: 24 KTS AT 281730Z

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

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: TD 20W WILL CONTINUE TRACKING
WEST-NORTHWESTWARD INITIALLY AND GRADUALLY TURN TOWARD A WESTWARD 
TRACK THROUGH THE FORECAST PERIOD UNDER THE CONTINUED STEERING 
INFLUENCE OF ENTRENCHED SUBTROPICAL RIDGE TO THE NORTH. 
INTENSIFICATION IS EXPECTED OVER THE NEXT 24 HOURS DUE TO PASSAGE
OVER WARM WATER AND IMPROVED POLEWARD OUTFLOW. HOWEVER, PERSISTENT 
EASTERLY VERTICAL WIND SHEAR AND THE BROAD NATURE OF THE LOW-LEVEL 
CIRCULATION, WHICH HAS JUST BEGUN TO CONSOLIDATE AROUND A DISTINCT 
CENTER, WILL LIMIT THE INTENSIFICATION RATE. INCREASING VERTICAL WIND 
SHEAR SHOULD HALT THE INTENSIFICATION TREND BY TAU 36, WITH THE 
SYSTEM MAKING LANDFALL SHORTLY THEREAFTER. FULL DISSIPATION OVER LAND 
IS ANTICIPATED BY TAU 72. 

MODEL DISCUSSION: DETERMINISTIC CONSENSUS AND ENSEMBLE MODEL TRACK
FORECAST SOLUTIONS ARE IN TIGHT AGREEMENT REGARDING BOTH THE
ANTICIPATED DIRECTION AND SPEED OF MOTION. GFS AND THE GEFS MEAN
SHOW THE SYSTEM CENTER PASSING A BIT CLOSER TO HAINAN ISLAND
BETWEEN TAUS 24 AND 36, BUT OTHERWISE THERE ARE NO NOTEWORTHY
DEVIATIONS IN THE GUIDANCE. MODEL INTENSITY FORECASTS ARE ALSO IN
GOOD AGREEMENT, WITH ALL PRIMARY MODELS INDICATING LIMITED, SLOW
INTENSIFICATION OVER THE NEXT 24 HOURS FOLLOWED BY A STEADY STATE
AND WEAKENING OVER LAND. THE CURRENT INTENSITY FORECAST LIES
SLIGHTLY ABOVE THE INTENSITY FORECAST CONSENSUS, CONSISTENT WITH
PREVIOUS FORECASTS AND ENVIRONMENTAL ASSESSMENT INDICATING A 
MARGINALLY FAVORABLE SCENARIO FOR NEAR-TERM INTENSIFICATION.

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