WDXS31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 03S (THREE) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.3S 67.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 368 NM WEST-SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) OF TROPICAL
CYCLONE (TC) 03S WITH FLARING CENTRAL CONVECTION SHEARED TO THE
SOUTHWEST. A 091615Z METOP-B ASCAT PASS DEPICTS A SLIGHTLY
CONSOLIDATED, YET STILL ASYMMETRICAL WIND FIELD, WITH MAXIMUM WINDS
LOCATED TO THE SOUTHWEST OF THE LLCC. ENVIRONMENTAL ANALYSIS
REVEALS MARGINALLY FAVORABLE ENVIRONMENT WITH WARM (26-27 C) SEA
SURFACE TEMPERATURES (SST) AND STRONG WESTWARD OUTFLOW, OFFSET BY
MODERATE TO HIGH (20-25 KTS) VERTICAL WIND SHEAR (VWS) AND DRY AIR
ENTRAINMENT FROM THE NORTHEAST. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON THE ANIMATED EIR, SUPPORTED BY THE
AFOREMENTIONED 091615Z ASCAT PASS. THE INITIAL INTENSITY OF 35 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND
OBJECTIVE INTENSITY ESTIMATED LISTED BELOW.

INITIAL WIND RADII BASIS: A 091615Z METOP-B ASCAT PASS

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) POSITIONED TO
THE SOUTH-SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   CIMSS ADT: 31 KTS AT 091800Z
   CIMSS AIDT: 38 KTS AT 091700Z
   CIMSS D-MINT: 28 KTS AT 091422Z
   CIMSS D-PRINT: 28 KTS AT 091830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG WESTWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE NORTHEAST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 03S IS FORECAST TO TRACK GENERALLY WESTWARD
UNDER THE BROAD RIDGING AREA TO THE SOUTH. AS AN UPPER LEVEL TROUGH
IS TEMPORARILY CAUSING A BREAK IN THE RIDGE DIRECTLY TO THE SOUTH,
TC 03S IS MAKING A SLIGHT WEST-SOUTHWESTWARD TURN. HOWEVER, WITHIN
THE NEXT 12-24 HOURS RIDGING IS EXPECTED TO BUILD AGAIN AND EXTEND
SOUTH OF TC 03S. AS A RESULT, AROUND TAU 24, THE SYSTEM IS EXPECTED 
TO TURN WEST-NORTHWESTWARD AND TRACK ALONG THE NORTHERN PERIPHERY OF 
THE RIDGE THROUGHOUT THE FORECAST PERIOD. IN REGARD TO INTENSITY, TC
03S IS FORECAST TO OSCILLATE AROUND 35-40 KTS, WITH SLIGHT
INTENSIFICATION EXPECTED WITHIN THE NEXT 24-36 HOURS, AS THE SYSTEM
MOVES WESTWARD AND AWAY FROM THE DRY AIR. AROUND TAU 96, TC 03S WILL
ENCOUNTER COOLER WATERS (25-26 C SST), INCREASING VERTICAL WIND
SHEAR, AS WELL AS MORE DRY AIR ERODING THE VORTEX FROM THE NORTH.
AS A RESULT, THE SYSTEM IS EXPECTED TO BEGIN WEAKENING AND
DISSIPATE BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT IN REGARD TO THE GENERAL TRAJECTORY, HOWEVER UNCERTAINTY
ASSOCIATED PARTICULARLY WITH THE ALONG-TRACK SPREAD RESULTS IN
OVERALL LOW CONFIDENCE IN THE LONG-TERM TRACK FORECAST. CROSS-TRACK
SPREAD IS ESTIMATED AT 125 NM AT TAU 48, EXPANDING TO OVER 250 NM
BY THE END OF THE FORECAST PERIOD. ALONG-TRACK SPREAD AT TAU 120 IS
ESTIMATED AT OVER 300 NM FURTHER ADDING TO TRACK UNCERTAINTY. IN
TERMS OF INTENSITY, JTWC FORECAST IS ASSESSED WITH OVERALL MEDIUM
CONFIDENCE WITH MAJORITY OF THE AVAILABLE GUIDANCE SHOWING A STEADY
30-40 KTS MAXIMUM WIND SPEED VALUES THROUGHOUT THE FORECAST PERIOD.
JTWC INTENSITY FORECAST IS LAID CLOSE TO THE MULTI-MODEL CONSENSUS,
JUST BELOW THE GUIDANCE FROM HAFS AND HWRF, WHILE SLIGHTLY ABOVE
COAMPS, PARTICULARLY BEYOND THE INITIAL 24 HOURS. GFS DETERMINISTIC
GUIDANCE ALSO SHOWS BORDERLINE WARNING CRITERIA INTENSITIES OF
30-35 KTS THROUGHOUT THE CURRENT FORECAST PERIOD.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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