WDPN31 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) 
WARNING NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.3N 109.3E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 97 NM NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 20 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL DEPRESSION 20W IS CHUGGING ALONG IN THE WESTERN HALF OF
THE SOUTH CHINA SEA AND CONTINUING TO BEHAVE PREDICTABLY. AS
TROPICAL CYCLONES GO IT IS ON THE DULL END OF THE SPECTRUM.
NONETHELESS, THE WARM SURFACE WATERS IN THE REGION AND DEEP
MOISTURE THROUGHOUT THE COLUMN ARE ALLOWING THE SYSTEM TO WHIP UP
10-15FT SEAS AND NEAR-GALE FORCE WINDS. THERE IS SOME SHEAR WORKING
ON THE STORM, BUT THE LATEST WATER VAPOR ANIMATION SHOWS A DISTINCT
LINE DEVELOPING ON THE UPSHEAR SIDE, INDICATING THE SYSTEM IS
MANAGING TO HOLD ITS OWN AGAINST THE 15-20 KNOTS OF NORTHEASTERLY
SHEAR.  ANIMATED INFRARED IMAGERY EVEN SHOWS SIGNS THAT THE LOW
LEVEL CIRCULATION CENTER IS COMING BACK UNDER THE CONVECTIVE
CANOPY. STILL, THE SHEAR IS CAUSING THE DEEP CONVECTION TO BE 
CONCENTRATED IN THE SOUTHERN HEMISPHERE OF THE CIRCULATION.  A
291804Z AMSR2 SERIES SHOWS THE DEARTH OF CONVECTION OVER THE
NORTHWEST QUADRANT AND ALSO WORKS WELL TO CONFIRM SYSTEM PLACEMENT.
A 291417Z SCATTEROMETRY PASS SHOWED THAT THE STRONGEST WINDFIELDS
WERE OVER THE NORTH AND NORTHWEST QUADRANTS, REMOVED FROM THE
DEEPEST CONVECTION, BUT THE DIFFERENCE IN WINDFIELDS FROM ONE
HEMISPHERE TO ANOTHER ARE ONLY 5 TO 10 KNOTS, INDICATING THE CORE
IS ESTABLISHED WELL ENOUGH TO MAINTAIN INTEGRITY.

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

CURRENT STEERING MECHANISM: THE EXTREME SOUTHWESTERN FLANK OF THE
SUBTROPICAL RIDGE. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 39 KTS AT 291804Z
   CIMSS ADT: 35 KTS AT 291730Z
   CIMSS AIDT: 34 KTS AT 291730Z
   CIMSS D-MINT: 27 KTS AT 291804Z
   CIMSS D-PRINT: 27 KTS AT 291830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 17 KTS
   SST: 27-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 10W WILL SUSTAIN 12 TO 18
KNOTS OF SPEED ALONG A STEADY LINE OF BEARING, WITH THE VORTEX
MAKING LANDFALL JUST NORTH OF DONG HOI RIGHT AROUND THE LOCAL SUNSET 
TIME. THE WARM WATERS ALONG TRACK AND A LITTLE BIT OF EASING OF THE 
SHEAR WILL ALLOW THE SYSTEM TO RAMP UP TO LOW GALE FORCE JUST PRIOR 
TO LANDFALL. STORM STRUCTURE INDICATES THE HEAVIEST RAINFALL AND 
CONVECTIVE HAZARDS WILL BETWEEN THE VORTEX AND HUE CITY. ONCE INLAND 
THE SYSTEM WILL WEAKEN RAPIDLY AND LIKELY NOT BE FINDABLE BY THE TIME 
IT CROSSES THE RUGGED 1500-2000 FT HILLS IN LAOS. INTERESTINGLY, 850MB 
VORTICITY FIELDS FROM MULTIPLE MODELS AND THE ECMWF ENSEMBLE CARRY THE 
ENERGY ALL THE WAY INTO THE BAY OF BENGAL, WHICH MAY MAKE FOR A FALL 
KICK OFF IN THE BAY OF BENGAL. ONE CAN ALMOST SMELL THE FOOTBALL IN 
THE AIR.  

MODEL DISCUSSION: MODELS ARE IN TIGHT AGREEMENT ON BOTH TRACK AND
INTENSITY AND HAVE A MORE MINOR INFLUENCE ON THIS FORECAST THAN IS
TYPICAL. SYNOPTIC ANALYSIS AND MOMENTUM PROVIDE THE BEST SOURCE OF
REASONING FOR THE CURRENT FORECAST. 

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