WDPN33 PGTW 280300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TWENTY) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.7N 125.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 370 NM NORTHEAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY REVEALS A
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) TO THE
NORTHWEST OF THE COLD DENSE OVERCAST ASSOCIATED WITH TS
20W. OVER THE LAST SIX HOURS THE SYSTEM SLOWED DOWN AND IS LOCATED
WITHIN A COL REGION BETWEEN TWO DEEP-LAYER SUBTROPICAL RIDGES. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED
INFRARED IMAGERY, AS WELL AS THE 272143Z SSMIS 37GHZ MICROWAVE PASS.
THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON OVERALL ASSESSMENT OF THE AGENCY AND AUTOMATED FIXES LISTED 
BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: IN A COL BETWEEN THE EASTERN SIDE OF A
DEEP-LAYER STR LOCATED OVER THE SOUTH CHINA SEA AND NORTH-WESTERN
SIDE OF A DEEP-LAYER STR EAST OF THE PHILIPPINES.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 37 KTS AT 280100Z
   CIMSS ADT: 37 KTS AT 272330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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: AS THE RIDGE OVER THE SOUTH CHINA SEA RETRACTS
WESTWARD, TS 20W IS FORECAST TO START TRACKING WEST-NORTHWESTWARD
BEFORE MAKING A NORTH-NORTHWESTWARD TURN BY TAU 48 AS THE STR EAST OF 
THE PHILIPPINES ASSUMES STEERING. AFTER THAT, TS 20W IS FORECAST TO 
TRACK NORTHWARD AND RECURVE TO THE NORTHEAST, PARALLEL TO THE EASTERN 
COASTLINE OF TAIWAN. EXPECTED PEAK INTENSITY IS 105 KTS BY TAU 96. 
CURRENT INTENSITY PREDICTION IS SLIGHTLY LOWER THAN LAST WARNING DUE 
TO ENVIRONMENTAL CONDITIONS BECOMING LESS FAVORABLE THAN PREVIOUSLY 
FORECAST. BEGINNING TAU 48, VERTICAL WIND SHEAR IS EXPECTED TO 
INCREASE TO 25 KTS. AFTER TAU 72, TS 20W WILL ENCOUNTER A BROAD AREA 
OF DRY AND COLDER AIR TO THE WEST AND NORTH AND THE SUBSIDING EFFECT 
OF A MID-LATITUDE TROUGH DIGGING IN FROM THE NORTHWEST, OFFSETTING THE 
PRIMARILY FAVORABLE SEA SURFACE TEMPERATURES AND OCEAN HEAT CONTENT, 
INHIBITING DEVELOPMENT TOWARD THE EXTENDED PORTION OF THE FORECAST. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE REMAINS IN FAIR
AGREEMENT, WITH SLIGHT TRACK DISCREPANCY STILL PRESENT AMONG THE
CONSENSUS MEMBERS. THE TIMING OF THE STEERING PATTERN DEVELOPMENT
REMAINS DIFFERENT AMONG THE GFS AND ECMWF MEMBERS. ECMWF CONTINUES
TO FORECAST THE TRACK OVER TAIWAN, ALBEIT SLIGHTLY FURTHER EAST
THAN PREVIOUS RUNS. GFS HOWEVER STILL FORECASTS THE TRACK TO BE
OVER 100 NM EAST OF TAIWAN. JTWC TRACK FORECAST IS PLACED
MARGINALLY EASTWARD OF THE MULTI-MODEL CONSENSUS ACCOUNTING FOR GFS
SOLUTION PREFERENCE. INTENSITY GUIDANCE IS PLACED SLIGHTLY ABOVE
THE MULTI-MODEL CONSENSUS, BUT LOWER THAN FORECAST DURING PREVIOUS
WARNING CYCLE DUE TO MODEL GUIDANCE SHOWING INCREASING SHEAR AND
APPROACHING DRY AIR REGION BY TAU 48.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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