WDPN31 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (PABUK) WARNING 
NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.4N 111.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 291 NM EAST OF HO CHI MINH CITY, VIETNAM
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A HIGHLY
ASYMMETRIC SYSTEM, WITH A PARTIALLY EXPOSED LOW LEVEL CIRCULATION
CENTER (LLCC) MOVING BACK OUT FROM UNDER THE CIRRUS SHIELD
ASSOCIATED WITH DEEP CONVECTION ALONG THE COAST OF VIETNAM. THE
LLCC IS EXTREMELY WEAK AND ONLY EVIDENT IN HIGH RESOLUTION
SHORTWAVE INFRARED (SWIR) IMAGERY, HAVING DETERIORATED
SIGNIFICANTLY DURING ITS TIME UNDER THE CIRRUS SHIELD. A LACK OF
RECENT SCATTEROMETER DATA PRECLUDES A FULL UNDERSTANDING OF THE
WIND FIELD, BUT GLOBAL AND HURRICANE MODEL FIELDS SUGGEST SOME
POSSIBLE GALE-FORCE WINDS MAY BE EMBEDDED IN THE COASTALLY TRAPPED
NORTHERLY SURGE FLOW TO THE WEST OF THE CENTER. THIS IS MADE ALL
THE MORE LIKELY DUE TO THE DEEP CONVECTION THAT HAS PERSISTED IN
THAT PORTION OF THE CIRCULATION FOR THE PAST SIX HOURS. HOWEVER,
THE REMAINDER OF THE WIND FIELD IS SIGNIFICANTLY WEAKER BASED ON
EARLIER SCATTEROMETER DATA AND JUDGING FROM THE OVERALL STRUCTURAL
APPEARANCE OF THE SYSTEM. THE INITIAL POSITION IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC AND ANALYSIS OF
A 241054Z SSMIS 91GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS
ASSESSED WITH MEDIUM CONFIDENCE, BASED ON THE AVERAGE OF THE
SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED BELOW. THE
ENVIRONMENT CONTINUES TO REMAIN UNFAVORABLE, WITH MODERATE
SOUTHEASTERLY SHEAR, LIMITED OUTFLOW ALOFT AND MARGINAL (26-27C)
SSTS.

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

CURRENT STEERING MECHANISM: COMBINATION OF THE LOW- TO MID-LEVEL
FLOW ON THE WESTERN SIDE OF A DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED FAR TO THE EAST AND THE LOW-LEVEL SURGE FLOW TO THE WEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 35 KTS AT 240830Z
   CIMSS ADT: 37 KTS AT 241200Z
   CIMSS AIDT: 34 KTS AT 241200Z
   CIMSS D-MINT: 31 KTS AT 241056Z
   CIMSS D-PRINT: 35 KTS AT 241200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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: TROPICAL DEPRESSION (TD) 28W (PABUK) CONTINUES
TO TRACE AN ERRATIC MOTION OVER THE PAST 12 HOURS, WITH THE
GENERALLY LIGHT STEERING INFLUENCE OF THE STR FAR TO THE EAST
COMPETING WITH THE BLOCKING EFFECT OF THE NORTHERLY SURGE FLOW
TRAPPED ALONG THE COAST OF VIETNAM. GLOBAL MODELS ARE STILL SHOWING
THAT WHILE THE NORTHERLY SURGE FLOW WILL REMAIN IN PLACE, IT WILL
RAPIDLY WEAKEN OVER THE NEXT 12-18 HOURS. AT THE SAME TIME, IN THE
LOW- TO MID-LEVELS, THE STEERING PATTERN SHIFTS AS A NEW
ANTICYCLONE DEVELOPS OVER MYANMAR AND MOVES QUICKLY EASTWARD,
RESULTING IN A DEEPER NORTHEASTERLY STEERING LAYER. TD 28W IS THUS
EXPECTED TO CONTINUE TRACKING TOWARDS THE SOUTHWEST ALONG THIS
MODERATELY DEEP NORTHEASTERLY STEERING VECTOR, THROUGH THE DURATION
OF THE FORECAST PERIOD. WINDS IN THE UPPER-LEVELS HOWEVER ARE
COMING STRAIGHT OUT OF THE SOUTHEAST AND INCREASING IN SPEED. AN
UPSTREAM OUTAGE HAS RESULTED IN AN ATMOSPHERIC MOTION VECTOR (AMV)
OUTAGE, AND THUS MEASURED SHEAR VALUES, BUT MODEL-DERIVED SOUNDINGS
SUGGEST SHEAR IS CURRENTLY RUNNING AT AROUND 25 KNOTS AND THESE
VALUES ARE FORECAST TO CONTINUE TO INCREASE OVER THE NEXT 12 TO 24
HOURS. A SLIVER OF RELATIVELY DRY MID-LEVEL AIR IS ALSO PRESENT TO
THE SOUTHEAST OF THE SYSTEM AND WILL BE PUSHED IN WITH THE STRONG
SOUTHEASTERLY FLOW, IN EFFECT SMOTHERING THE SYSTEM. WITH STRONG
SHEAR AND DRY AIR ALOFT, THE SYSTEM WILL NOT BE ABLE TO RECOVER AND
WILL QUICKLY DISSIPATE AS IT MOVES ALONG THE COAST OF VIETNAM. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL TRACK SOUTHWESTWARD THROUGH THE FORECAST
PERIOD AND REMAIN OFFSHORE AS IT DISSIPATES BELOW WARNING CRITERIA.
AFTER THE FINAL POINT IN THE FORECAST, THE REMNANT VORTEX IS LIKELY
TO PASS OVER THE SOUTHERN PORTION OF THE MEKONG DELTA AND MOVE INTO
THE SOUTHERN GULF OF THAILAND BUT IS EXPECTED TO REMAIN VERY WEAK.
INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH ALL GUIDANCE
EXCEPT THE HWRF (WHICH REDEVELOPS THE SYSTEM IN THE GULF OF
THAILAND) INDICATING DISSIPATION WITHIN THE NEXT 24 TO 48 HOURS. 

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