WDPN33 PGTW 272100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TWENTY) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.1N 125.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 382 NM NORTHEAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
STEADILY CONSOLIDATING TS 20W, WITH SPIRAL BANDS OF DEEP CONVECTION
COVERING THREE QUADRANTS OF THE SYSTEM AND WRAPPING INTO THE
LOW-LEVEL CIRCULATION CENTER (LLCC). STRONGEST CONVECTIVE ACTIVITY
IS PRESENT ON THE SOUTHWESTERN SIDE OF TS 20W, CLOSE TO LUZON.
SYSTEM IS CURRENTLY POSITIONED IN BETWEEN A DEEP-LAYER SUBTROPICAL
RIDGE OVER THE SOUTH CHINA SEA AND A SLOWLY DEVELOPING RIDGE TO THE
SOUTHEAST OF THE SYSTEM. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON LOW CLOUD TRACING INTO AN OBSCURED LLCC IN 
THE ANIMATED INFRARED IMAGERY, AS WELL AS 271330Z ASCAT-C PASS. THE 
INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED 
ON AFOREMENTIONED ASCAT-C PASS, AS WELL AS THE AGENCY AND AUTOMATED 
FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: RECENT SCATTEROMETRY DATA.

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: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 36 KTS AT 271800Z
   CIMSS ADT: 33 KTS AT 271800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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: TS 20W IS FORECAST TO CONTINUE SLOWLY TRACKING
SOUTHWESTWARD, STEERED BY THE STR OVER THE SOUTH CHINA SEA. MODEL
GUIDANCE SHOWS A WESTWARD MOVEMENT OF THE RIDGE OVER THE NEXT 36
HOURS. DURING THAT TIME, A STR EAST OF THE PHILIPPINES WILL BUILD
AND START BECOMING THE PRIMARY STEERING FEATURE FOR TS 20W, AS IT
THEN MAKES A NORTHWESTWARD TURN SOUTHEAST OF TAIWAN. DISAGREEMENT
BETWEEN THE TIMING, MOVEMENT AND DEVELOPMENT OF BOTH RIDGES DIFFERS
BETWEEN ECMWF AND GFS SOLUTIONS, WITH THE FORMER LEADING TO A TRACK
RIGHT OVER TAIWAN, WHILE THE LATTER SHOWS A WEAKER RIDGE OVER
CHINA, STRONGER STEERING INFLUENCE OF THE RIDGE OVER THE PHILIPPINE
SEA, LEADING TO TS 20W TRACK REMAINING EAST OF TAIWAN. IN TERMS
OF INTENSITY, ANALYSIS PRESENTS A FAVORABLE ENVIRONMENT, WITH LOW
NORTHEASTERLY VERTICAL WIND SHEAR, WARM SSTS AND GOOD SOUTHWESTWARD
AND EQUATORWARD OUTFLOW. THEREFORE, TS 20W IS FORECAST TO STEADILY
INTENSIFY OVER THE COURSE OF AT LEAST 96 HOURS DRIVEN BY THE
FAVORABLE ENVIRONMENTAL CONDITIONS, REACHING PEAK INTENSITY OF 110
KTS. INCREASING WIND SHEAR AND WIND FIELD LAND INTERACTION OVER THE
NORTHWESTERN PORTION OF TAIWAN WILL THEN LEAD TO A WEAKENING TREND.

MODEL DISCUSSION: DETERMINISTIC TRACK MODEL GUIDANCE IS IN FAIR
AGREEMENT, WITH OVERALL SIMILAR TRACK PATTERN, WHILE THE
DISCREPANCY BETWEEN GFS AND ECMWF IN REGARDS TO STEERING MECHANISMS
DEVELOPMENT LEADS TO SOME UNCERTAINTY IN TERMS OF THE TIMING OF THE
RECURVING MOTION OF THE STORM. AT THE SAME TIME, THE MORE EASTERLY
TRACK THE STORM TAKES, THE MORE THERE IS POTENTIAL FOR FURTHER
INTENSIFICATION. JTWC TRACK FORECAST IS LAID IN CLOSE PROXIMITY TO
THE MULTI-MODEL CONSENSUS, HEDGING TOWARDS THE MORE REALISTIC GFS
SOLUTION, TAKING THE STORM EAST OF TAIWAN. AT THE SAME TIME, IN
TERMS OF INTENSITY GUIDANCE, JTWC FORECAST IS ON THE HIGHER END OF
THE CONSENSUS, GIVEN THE FAVORABLE ENVIRONMENT, WITH JUST THE HAFS
GUIDANCE FORECASTING NEARLY 130 KTS PEAK INTENSITY. OVERALL
INTENSITY MODEL GUIDANCE IS IN GOOD AGREEMENT IN TERMS OF TIMING
AND LEVEL OF INTENSIFICATION.

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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