WDPN31 PGTW 272100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.3N 113.6E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 380 NM SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION, AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED
WITH TROPICAL STORM (TS) 33W (KOTO). RAPIDLY WARMING CLOUD TOPS
INDICATE A BEGINNING OF A WEAKENING TREND, AMPLIFIED BY THE
DECOUPLING OF THE CENTRAL CONVECTION, DUE TO STRONG (20-25 KTS)
SOUTHEASTERLY VERTICAL WIND SHEAR (VWS). ADDITIONAL ENVIRONMENTAL
ANALYSIS REVEALS DRY AIR ENTRAINMENT PARTICULARLY EVIDENT
THROUGHOUT THE SOUTHEASTERN QUADRANT. SEA SURFACE TEMPERATURES
(SST) REMAIN WARM (28-29 C) AND POLEWARD OUTFLOW REMAINS STRONG,
BOTH OFFSETTING THE OTHERWISE INCREASINGLY HOSTILE ENVIRONMENT. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
WRAPPING OF LOW-LEVEL BANDING OBSERVED IN A 271648Z GPM GMI
MICROWAVE PASS. THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON A COMBINATION OF AGENCY FIXES AND
OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT WITH RIDGING
TO THE EAST AND WEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   DEMS: T4.0 - 65 KTS
   CIMSS SATCON: 53 KTS AT 271817Z
   CIMSS ADT: 51 KTS AT 271730Z
   CIMSS AIDT: 58 KTS AT 271730Z
   CIMSS D-MINT: 55 KTS AT 271817Z
   CIMSS D-PRINT: 47 KTS AT 271930Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT OVER THE EASTERN QUADRANT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: WEAK AND COMPETING SYNOPTIC STEERING
MECHANISMS WILL RESULT IN CONTINUOUS ERRATIC MEANDERING SOUTHWARD
AND NORTHWARD ALONG THE OVERALL WESTWARD TRAJECTORY OF TS KOTO.
AROUND TAU 72 THE SUBTROPICAL RIDGE (STR) CENTERED OVER SOUTHEAST
ASIA IS EXPECTED TO DOMINATE THE STEERING AND PROPEL THE SYSTEM
TOWARDS LANDFALL OVER EASTERN VIETNAM. IN TERMS OF INTENSITY, THE 
SYSTEM IS NOW ENCOUNTERING INCREASINGLY HIGH VWS WHICH HAS DECOUPLED 
THE EXISTING CENTRAL CONVECTION. ADDITIONALLY, DRY AIR INTRUSION IS 
AFFECTING THE STRUCTURE OF THE VORTEX, INHIBITING INTENSIFICATION. 
AFTER TAU 36, A SHORT WINDOW OF OPPORTUNITY OPENS UP, WITH LOWER VWS 
IMPACTS, OFFSET HOWEVER BY CONTINUOUS DRY AIR ENTRAINMENT AND 
POTENTIAL IMPACT FROM THE UPWELLING BRINGING COLDER WATER TO THE OCEAN 
SURFACE BENEATH THE STORM. AFTER TAU 96, VWS IS EXPECTED TO INCREASE 
AGAIN RESULTING IN FURTHER WEAKENING.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN FAIR
AGREEMENT, WITH MAJORITY OF THE MODELS DEPICTING A NORTHWESTWARD
TURN TO OCCUR SHORTLY AFTER TAU 12, FOLLOWED BY A TRACK TOWARDS
VIETNAM BEGINNING AROUND TAU 72. THE MAJOR OUTLIERS TO THIS
GUIDANCE ARE GFS AND GFS ENSEMBLE, WHICH BOTH PORTRAY THE SYSTEM
REMAINING NEARLY QUASI-STATIONARY OVER THE NEXT 72-96 HOURS, PRIOR TO
MAKING A WESTWARD TURN. THE OFFICIAL JTWC TRACK IS ASSESSED WITH
MEDIUM CONFIDENCE THROUGHOUT THE FORECAST. IN TERMS OF INTENSITY,
ALL MODELS PREDICT A STEADY WEAKENING TREND THROUGH TAU 48,
RESULTING IN FAIR CONFIDENCE. GIVEN THE CURRENT ENVIRONMENT, THE
STEEPNESS OF THE TREND MAY HOWEVER BE A LITTLE TOO CONSERVATIVE.
AFTER TAU 48, TWO MODELS INDICATE INTENSIFICATION TREND, WITH HAFS
SHOWING AN AGGRESSIVE PEAK OF 75-80 KTS, WHILE GFS BRINGS THE 
INTENSITY BACK TO 60 KTS. ALL OF THE OTHER CONSENSUS MEMBERS INDICATE 
STEADY WEAKENING, LIKELY DRIVEN BY COOLER WATER UPWELLING, IMPACTS OF 
DRY AIR AND INCREASING VWS. AS A RESULT, LONG-TERM INTENSITY
FORECAST IS ASSESSED WITH LOW CONFIDENCE, WHILE THE SHORT TERM IS
PREDICTED WITH MEDIUM CONFIDENCE, DUE TO BETTER GUIDANCE AGREEMENT.
JTWC OFFICIAL INTENSITY FORECAST IS LAID WITHIN 5 KTS OF THE
MULTI-MODEL CONSENSUS.

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