WDPN31 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.0N 112.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 289 NM SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SYSTEM
THAT IS WELL-ORGANIZED IN THE OVERALL SENSE, WITH A BROAD CYCLONIC
ROTATION EVIDENT ALONG THE OUTER EDGES OF THE CIRRUS SHIELD. THE
CENTRAL DENSE OVERCAST (CDO) FEATURE SEEN EARLIER HAS COLLAPSED, AS
EVIDENCED BY THE RAPID WARMING OF THE UPPER-LEVEL CLOUDS AND
ACCOMPANYING LACK OF ORGANIZATION. UNDER THE HOOD, A 282353Z SSMIS
91GHZ MICROWAVE IMAGE REVEALS A HIGHLY DISORGANIZED STRUCTURE, WITH
FRAGMENTED CONVECTIVE BANDING FEATURES SCATTERED ACROSS THE WESTERN
HEMISPHERE OF THE SYSTEM, WITH THE MOST DEFINED LOW-LEVEL BANDS
PRESENT ON THE NORTHERN SIDE OF THE INNER-CORE. THE EASTERN FLANK
OF THE SYSTEM IS DEVOID OF SIGNIFICANT CONVECTION, AND BOTH THE
MICROWAVE IMAGE AND THE MSI DEPICT A LARGE WEDGE OF DRY AIR
WRAPPING UP FROM THE SOUTH ALONG THE EASTERN FLANK. THE SYSTEM IS
SLOWLY DRIFTING NORTHWARD AT 1-2 KNOTS BASED ON A SERIES OF
MICROWAVE IMAGES OVER THE PAST 6 HOURS. THE INITIAL POSITION IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN DERIVED ARCHER FIX AND
ANALYSIS OF THE 37GHZ IMAGE OF THE MICROWAVE IMAGE NOTED ABOVE. THE
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON A
BLEND OF THE AVAILABLE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES
NOTED BELOW. ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE,
WITH LOW EASTERLY WIND SHEAR AND DECENT POLEWARD OUTFLOW OFFSET BY
THE INFLUENCE OF DRY MID-LEVEL AIR AND SIGNIFICANT OCEANIC
UPWELLING, WHICH IS RAPIDLY COOLING THE SSTS NEAR THE CORE OF TS
33W.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK AND COMPETING STEERING PATTERN,
CAUGHT BETWEEN A SUBTROPICAL RIDGE (STR) IN THE PHILIPPINE SEA AND
A STR OVER SOUTHERN MYANMAR. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS SATCON: 50 KTS AT 282236Z
   CIMSS ADT: 37 KTS AT 290030Z
   CIMSS AIDT: 37 KTS AT 290030Z
   CIMSS D-MINT: 38 KTS AT 282354Z
   CIMSS D-PRINT: 40 KTS AT 290100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR IN THE EASTERN FLANK. 

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: TS 33W IS DRIFTING NORTHWARD, EMBEDDING WITHIN
A WEAK AND COMPETING STEERING PATTERN. OVER THE NEXT 12 TO 24
HOURS, RIDGING IS EXPECTED TO SLOWLY BUILD OVER THE NORTH-CENTRAL
PHILIPPINES, EVENTUALLY CONNECTING UP WITH THE BUILDING NER OVER
BORNEO AND ESTABLISHING A NORTHEAST-SOUTHWEST ORIENTED RIDGE
COMPLEX. TS 33W WILL TRACK STEADILY, BUT SLOWLY, NORTHWARD FOR THE
NEXT 36 TO 48 HOURS ALONG THE WESTERN SIDE OF THE BUILDING RIDGE
OVER LUZON. BY TAU 48, THE RIDGE CENTER BEGINS TO SLIDE WESTWARD
WHILE SIMULTANEOUSLY EXTENDING WEST OVER HAINAN AND ESTABLISHING A
BLOCKING RIDGE TO THE NORTH OF TS 33W. THE EVOLUTION OF THE RIDGING
PATTERN WILL BLOCK TS 33W FROM TRANSITING FURTHER NORTH AFTER TAU
36, WITH THE SYSTEM SLOWING TO QUASI-STATIONARY SPEEDS AS IT
REACHES AN INFLECTION POINT IN ITS TRACK MOTION BETWEEN TAU 36 AND
TAU 48. BY TAU 48, THE PRIMARY STEERING INFLUENCE SHIFTS TO THE STR
CENTERED OVER SOUTHERN MYANMAR, NORTHERN THAILAND BORDER REGION AND
QUICKLY TRANSITIONS FROM A QUASI-STATIONARY TO A SOUTHWESTWARD
TRACK MOTION. THE SYSTEM THEN ACCELERATES SOUTHWESTWARD THROUGH THE
REMAINDER OF THE FORECAST PERIOD AS THE STEERING GRADIENT
STRENGTHENS ON THE WESTERN FLANK OF TS 33W. LANDFALL ALONG THE
COAST OF SOUTHERN VIETNAM IS EXPECTED AROUND TAU 96 WITH THE SYSTEM
CONTINUING INLAND ROUGHLY PARALLEL TO THE COAST THROUGH THE END OF
THE FORECAST PERIOD. WITH THE ENVIRONMENTAL CONDITIONS OFFSETTING
ONE ANOTHER, NO SIGNIFICANT CHANGE IN INTENSITY IS EXPECTED FOR THE
NEXT 24 HOURS. A BRIEF WINDOW OF OPPORTUNITY FOR INTENSIFICATION
OPENS UP AROUND TAU 36, AS THE SYSTEM TAPS INTO SOME WEAK
DUAL-CHANNEL OUTFLOW AND MOVES AWAY FROM THE UPWELLING INDUCED
COLD-POOL, BUT THE WINDOW WILL BE FLEETING AND THE SYSTEM IS NOT
EXPECTED TO INTENSIFY BEYOND 50 KNOTS. SHEAR INCREASES SHARPLY,
ALONG WITH AN INFLUX OF DRY AIR AFTER TAU 72, LEADING TO STEADY
WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD. BY TAU 120,
THE SYSTEM WILL BE NEARING DISSIPATION OVER SOUTHERN VIETNAM. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN RELATIVELY GOOD
AGREEMENT THROUGH TAU 48, WITH ALL MODELS INDICATING A SLOW
NORTHWARD PROGRESSION AND AN INFLECTION POINT BETWEEN TAU 36 AND
TAU 48. THE GALWEM MODEL IS POSITIONED ON THE WESTERN EDGE OF THE
MODEL PACKAGE, WITH THE ECMWF-AIFS ON THE EASTERN EDGE. UP TO THIS
POINT, THE JTWC FORECAST IS POSITIONED CLOSE TO THE CONSENSUS MEAN
WITH MEDIUM TO HIGH CONFIDENCE, THOUGH MORE ERRATIC MOTION AND
WOBBLING IS A POSSIBILITY DUE TO THE LACK OF A COHERENT AND STRONG
STEERING MECHANISM. AFTER TAU 48, THE MODELS RAPIDLY DISPERSE
ACROSS A VERY WIDE RANGE. THE NAVGEM AND GFS TRACK THE SYSTEM
ACROSS SOUTHEAST ASIA AND REACH THE GULF OF THAILAND BY TAU 120,
WHILE THE EGRR AND AIFS TURN THE SYSTEM EAST THEN SOUTHWEST, AND
KEEP THE 33W WELL OFFSHORE IN THE SOUTH CHINA SEA, OPENING UP A
CROSS-TRACK SPREAD OVER 600NM. THE REMAINDER OF THE GUIDANCE IS
ROUGHLY EQUALLY SPACED BETWEEN THE TWO OUTLIERS, LEADING TO A
HIGHLY UNCERTAIN FORECAST TRACK. THE JTWC TRACK IS POSITIONED NEAR
THE PREVIOUS FORECAST, AND THE CONSENSUS MEAN FROM TAU 48 TO 120,
WITH LOW CONFIDENCE. INTENSITY GUIDANCE IS IN GENERAL AGREEMENT ON
A FLAT INTENSITY FOR THE FIRST 24 HOURS, FOLLOWED BY A BRIEF PERIOD
OF INTENSIFICATION (PEAK BETWEEN 50-60 KNOTS), FOLLOWED BY STEADY
WEAKENING. THE JTWC FORECAST IS PLACED NEAR THE CONSENSUS MEAN
THROUGH THE FORECAST PERIOD WITH MEDIUM CONFIDENCE. 

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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