WDPN31 PGTW 301500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (KOTO) WARNING NR 
024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.4N 112.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 245 NM EAST-SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 33W (KOTO) WITH WEAK FLARING CONVECTION DISPLACED TO THE
SOUTH OF A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC).
SIGNIFICANT DRY AIR ENTRAINMENT AND UPWELLING EFFECTS HAVE TAKEN A
TOLL ON 33W OVER THE PAST 6 HOURS, WITH 33W APPEARING CONSIDERABLY
WEAKER. A 301050Z F16 SSMIS 91 GHZ MICROWAVE IMAGE REVEALED EXPOSED
LOW-LEVEL CLOUD LINES TO THE NORTH OF A SMALL POCKET OF DEEP
CONVECTION. ENVIRONMENTAL ANALYSIS INDICATES THAT 33W IS NOW IN A
MARGINAL ENVIRONMENT CHARACTERIZED BY WEAK OUTFLOW ALOFT, LOW
(10-15 KTS) VERTICAL WIND SHEAR, DRY AIR, AND UPWELLING. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
PARTIALLY EXPOSED LLCC IN ANIMATED EIR IMAGERY. THE INITIAL
INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
LOW END OF THE AGENCY DVORAK FIXES AND CIMSS OBJECTIVE INTENSITY
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS SATCON: 43 KTS AT 301050Z
   CIMSS ADT: 39 KTS AT 301200Z
   CIMSS AIDT: 33 KTS AT 301200Z
   CIMSS D-MINT: 39 KTS AT 301050Z
   CIMSS D-PRINT: 39 KTS AT 301200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD AND EQUATORWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT AND UPWELLING

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE SYSTEM IS FORECAST TO WEAKEN MORE
QUICKLY AND TAKE A SHARPER TURN TO THE SOUTHWEST THAN THE PREVIOUS
FORECAST. 33W IS NOW FORECAST TO DISSIPATE OVER WATER WITHOUT
MAKING A DIRECT LANDFALL IN VIETNAM.

FORECAST DISCUSSION: TS 33W IS FORECAST TO REMAIN IN A WEAK
STEERING ENVIRONMENT THROUGH TAU 48. THE SYSTEM IS FORECAST TO
SLOWLY DRIFT WESTWARD THROUGH TAU 24 BEFORE TURNING SOUTHWESTWARD
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
THROUGH TAU 72. THE TRACK OF 33W IS NOW ENTIRELY OVER WATER AS
MODELS DEPICT THE SHALLOW VORTEX TRACKING ALONG THE LOW-LEVEL
STEERING, WHICH HAS A MORE NORTH-SOUTH ORIENTATION. REGARDING
INTENSITY, 33W IS FORECAST TO MAINTAIN INTENSITY OVER THE NEXT 24
HOURS AS A BORDERLINE TROPICAL STORM STRENGTH SYSTEM. NEAR TAU 24,
DRY AIR ENTRAINMENT IS EXPECTED TO INCREASE EVEN FURTHER, CAUSING
33W TO STEADILY WEAKEN AND SHALLOW OUT. NEAR TAU 48, SOUTHEASTERLY
SHEAR IS EXPECTED TO INCREASE TO AROUND 15-20 KTS, AIDING IN
ADDITIONAL WEAKENING AS THE VORTEX ACCELERATES SOUTHWESTWARD.
DISSIPATION IS FORECAST TO OCCUR AROUND TAU 72, JUST OFF THE COAST
OF VIETNAM. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN POOR
AGREEMENT WITH CONSIDERABLE CROSS-TRACK AND ALONG-TRACK SPREAD. GDM
AND EC-AIFS ARE BOTH MUCH SLOWER THROUGH TAU 48 THAN THE REMAINDER
OF GUIDANCE. AT TAU 72, CROSS-TRACK SPREAD INCREASES TO AROUND 200
NM WITH NAVGEM MAKING UP THE WESTERNMOST MEMBER WHILE GDM MAKES UP
THE EASTERNMOST MEMBER. THE JTWC TRACK FORECAST IS PLACED CLOSE TO
THE GFS AND ECMWF ENSEMBLE MEANS WITH LOW CONFIDENCE. INTENSITY
GUIDANCE IS IN MODERATE AGREEMENT ON STEADY WEAKENING THROUGHOUT
THE FORECAST PERIOD. DECAY-SHIPS CONTINUES TO BE A MAJOR OUTLIER,
DEPICTING INTENSIFICATION, AND IS DISREGARDED FOR THIS MODEL RUN.
THE JTWC INTENSITY FORECAST IS PLACED IN LINE WITH THE BULK OF
GUIDANCE THROUGHOUT THE FORECAST PERIOD WITH MEDIUM CONFIDENCE.

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