WDPN31 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 
023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.3N 112.3E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 253 NM EAST-SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 33W (KOTO) WITH A WEAK CENTRAL CONVECTION WITH DEFINED
LOW-LEVEL CLOUD LINES TIGHTLY WRAPPING INTO THE CENTER. DRY AIR CAN
BE SEEN STREAMING FROM THE NORTH AND BEING PULLED INTO THE CORE OF
33W, LIKELY THE CAUSE OF THE WEAK CONVECTIVE STRUCTURE. A 300202Z
METOP-B ASCAT IMAGE REVEALED THAT THE EXTENT OF GALE-FORCE WINDS
HAS SIGNIFICANTLY SHRUNK OVER THE PAST 24 HOURS. THE ASCAT ALSO
REVEALED THAT THE STRONGEST WINDS ARE CONFINED TO THE NORTHEASTERN
QUADRANT, WITH AN ISOLATED PATCH OF 40 KNOT WIND BARBS IN THAT AREA. 
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
ANIMATED MSI. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED ASCAT IMAGE.
ADDITIONALLY, AGENCY DVORAK ESTIMATES OF T3.0-3.5 FURTHER SUPPORT
THE INITIAL INTENSITY ESTIMATE.

INITIAL WIND RADII BASIS: 300202Z METOP-B ASCAT DATA

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS SATCON: 51 KTS AT 300538Z
   CIMSS ADT: 37 KTS AT 300540Z
   CIMSS AIDT: 35 KTS AT 300540Z
   CIMSS D-MINT: 35 KTS AT 300538Z
   CIMSS D-PRINT: 45 KTS AT 300600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD AND EQUATORWARD
   OTHER FACTORS: UPWELLING AND DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 33W IS FORECAST TO REMAIN IN A WEAK
STEERING ENVIRONMENT THROUGH TAU 48. THE SYSTEM IS FORECAST TO
SLOWLY DRIFT GENERALLY WESTWARD THROUGH TAU 36 UNDER THE WEAK
INFLUENCE OF A SUBTROPICAL RIDGE (STR) CENTERED OVER THAILAND. NEAR
TAU 48, THE STR IS EXPECTED TO EXTEND EASTWARD AND MERGE WITH
ANOTHER STR WITHIN THE SOUTH CHINA SEA. ONCE THE RIDGING COMPLEX
BUILDS TO THE NORTH OF THE VORTEX, THE STEERING PATTERN WILL BECOME
MORE DEFINED, CAUSING 33W TO ACCELERATE SOUTHWESTWARD TOWARD THE
COAST OF VIETNAM. LANDFALL IS FORECAST TO OCCUR AROUND TAU 72.
AFTER TAU 72, 33W WILL CONTINUE TRACKING SOUTHWESTWARD AS IT TRACKS
TOWARD EASTERN CAMBODIA. REGARDING INTENSITY, 33W IS FORECAST TO
MAINTAIN INTENSITY THROUGH TAU 12 AS SHEAR REMAINS LOW. AFTER TAU
12, DRY AIR ENTRAINMENT FROM THE NORTH IS EXPECTED TO FURTHER
INCREASE, CAUSING 33W TO BEGIN STEADILY WEAKENING. NEAR TAU 48,
SOUTHEASTERLY SHEAR IS EXPECTED TO INCREASE TO AROUND 15-20 KTS,
AIDING IN ADDITIONAL WEAKENING AS THE VORTEX APPROACHES THE VIETNAM
COAST. AFTER LANDFALL, RUGGED TERRAIN INTERACTION WILL CAUSE 33W TO
DISSIPATE NO LATER THAN TAU 96. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN RELATIVELY
GOOD AGREEMENT THROUGH TAU 48 WITH THE EXCEPTION OF JGSM, WHICH
DEPICTS A MUCH FASTER TRACK SPEED THAN THE REMAINDER OF GUIDANCE.
AFTER TAU 48, MODELS DIVERGE WITH TO MAIN GROUPS OF MODELS. ECMWF,
AC-AIFS, AND GDM MAKE UP ONE GROUP AND TAKE THE SYSTEM NEARLY
STRAIGHT SOUTHWARD THROUGH TAU 72 BEFORE TURNING SOUTHWESTWARD,
KEEPING THE SYSTEM OVER WATER FOR A LONGER PERIOD. THE OTHER GROUP,
WHICH MAKES UP THE MAJORITY OF MODELS, TAKE A MORE
WEST-SOUTHWESTWARD TRACK TOWARD VIETNAM. THE JTWC TRACK FORECAST IS
HEDGED CLOSER TO THE SECOND GROUPING, AND CLOSE TO THE ECMWF
ENSEMBLE MEAN, WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND LOW
CONFIDENCE THEREAFTER. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON A
STEADY WEAKENING TREND AFTER TAU 12 (EXCEPT DECAY-SHIPS). THE JTWC 
INTENSITY FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS 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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