WDPN31 PGTW 232100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (PABUK) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.9N 112.1E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 324 NM EAST-NORTHEAST OF HO CHI MINH CITY,
VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED CIRA PROXY VISIBLE SATELLITE IMAGERY DEPICTS A SHALLOW AND 
FULLY EXPOSED VORTEX, JUST RECENTLY MAKING A WESTWARD TURN TOWARDS 
VIETNAM. AS THE SYSTEM LOST ITS VERTICAL EXTENT, IT IS BEING STEERED 
BY THE LOW-LEVEL FLOW, GENERALLY ASSOCIATED WITH A NORTHEASTERLY COLD 
SURGE RUNNING ALONG THE COAST OF EASTERN VIETNAM. AS DEPICTED BY THE 
231409Z METOP-B ASCAT PASS, TD PABUK IS APPROACHING A BAND OF 30 KT 
WINDS ASSOCIATED WITH THAT FLOW, WHILE THE WINDS DIRECTLY ENCOMPASSING 
THE LOW-LEVEL CIRCULATION CENTER (LLCC) REMAIN AT OR BELOW 25 KTS.
ADDITIONALLY, A FLARING AND PERSISTENT PATCH OF CONVECTION IN THE 
CONVERGENT REGION OF THE SURFACE FLOW DIRECTLY TO THE NORTH OF THE 
LLCC HAS DEVELOPED DURING LAST HOUR. TD PABUK IS CURRENTLY IN A 
MARGINAL ENVIRONMENT, WITH RELATIVELY WARM SEA SURFACE TEMPERATURES OF 
27-28 CELSIUS AND MODERATE VERTICAL WIND SHEAR OF 15-20 KTS, HOWEVER 
BOTH OF THOSE FACTORS WILL BECOME INCREASINGLY UNFAVORABLE FOR 
SUSTAINED DEVELOPMENT. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON THE NOTED FULLY EXPOSED LLCC. THE INITIAL 
INTENSITY OF 25 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON AGENCY 
ESTIMATES AND OBJECTIVE INTENSITY AIDS LISTED BELOW AND SUPPORTED BY 
THE EARLIER ASCAT DATA.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: 700 TO 850 MB MEAN LAYER FLOW

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T1.0 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS ADT: 27 KTS AT 231800Z
   CIMSS AIDT: 28 KTS AT 231800Z
   CIMSS D-PRINT: 28 KTS AT 231800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: NORTHEASTERLY COLD SURGE FLOW EXHIBITING 30 KTS
WIND SPEEDS, APPROXIMATELY 100-120 NM TO THE WEST OF LLCC

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TD PABUK IS FORECAST TO CONTINUE TURNING
WEST-SOUTHWESTWARD, FOLLOWED BY A TRACK INFLUENCED BY THE
NORTHEASTERLY LOW-LEVEL FLOW OVER THE NEXT 36 HOURS. AFTER THAT,
THE 700 TO 850 MB MEAN LAYER FLOW TO THE SOUTH OF THE SYSTEM WILL
STEER IT TOWARDS A LANDFALL OVER SOUTHERN VIETNAM. A FORECAST PEAK OF 
30 KTS IS INDICATED, GIVEN THE SLIGHT RESURGENCE OF CONVECTION AND THE 
FORECAST TRACK CLOSER TO THE 30 KT SURGE FLOW. HOWEVER, PAST TAU 24, 
THE ENVIRONMENT WILL BECOME STEADILY AND SIGNIFICANTLY LESS FAVORABLE 
FOR TROPICAL CYCLONE DEVELOPMENT, WITH COOLING SEA SURFACE 
TEMPERATURES, BROAD DRY AIR AND INCREASING VERTICAL WIND SHEAR. 
THEREFORE, TD PABUK IS FORECAST TO WEAKEN JUST PRIOR TO MAKING 
LANDFALL SHORTLY AFTER TAU 36, FOLLOWED BY COMPLETE DISSIPATION OVER 
LAND, COMPLETED BY TAU 48.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN GOOD
AGREEMENT WITH ALL TRACKERS PREDICTING WEST-SOUTHWESTWARD TRACK
WITH RELATIVELY TIGHT CROSS-TRACK SPREAD OF 73 NM THROUGHOUT TAU
36. BY TAU 48 NEARLY ALL MODELS ARE TRACKING THE SYSTEM OVER LAND,
WITH UKMET BEING THE ONLY OUTLIER STILL HAVING THE VORTEX OVER
WATER. JTWC TRACK FORECAST IS LAID WITH MEDIUM CONFIDENCE IN CLOSE 
PROXIMITY TO THE MULTI-MODEL CONSENSUS, JUST A TOUCH FASTER
AND THEREFORE, CLOSER TO GFS AND ECMWF GUIDANCE. JTWC INTENSITY
FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AVAILABLE
GUIDANCE, WITH NEARLY ALL MODELS PREDICTING SLIGHT INTENSIFICATION
OVER THE NEXT 12 HOURS, FOLLOWED BY A STEADYING TREND, ULTIMATELY
LEADING TO SHARP WEAKENING BEGINNING AT TAU 36.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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