WDPN32 PGTW 230300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.5N 111.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 225 NM SOUTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS
SLIGHTLY IMPROVED WITH DEEPENED CENTRAL CONVECTION THAT IS OFFSET
NORTHWESTWARD OF THE LOW LEVEL CIRCULATION THAT REMAINS OBSCURED.
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON LOW
CLOUD TRACING IN THE MSI LOOP AND TRIANGULATED FROM NEARBY SURFACE
WIND OBSERVATIONS.  THE INITIAL INTENSITY IS PLACED WITH MEDIUM
CONFIDENCE BASED ON OVERALL ASSESSMENT OF AGENCY AND AUTOMATED
DVORAK ESTIMATES AND THE SURFACE OBSERVATIONS, INCLUDING ONE FROM A 
SHIP JUST TO THE NORTHEAST REPORTING A 230000Z EASTERLY WIND OF 
28KTS, AND REFLECTS THE SLIGHT IMPROVEMENT. THE SYSTEM IS
IN A FAVORABLE ENVIRONMENT WITH LOW-MEDIUM VWS AND WARM SSTS OFFSET
BY WEAK OUTFLOW. THE CYCLONE IS TRACKING ALONG THE SOUTHERN
PERIPHERY OF THE LOW- TO MID-LEVEL REFLECTION OF THE  STR TO THE
NORTH.

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

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF THE LOW- TO
MID-LEVEL REFLECTION OF THE SUBTROPICAL RIDGE (STR) TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 222350Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND 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: TD 21W IS EXPECTED TO CONTINUE ON ITS CURRENT
TRACK AND MAKE LANDFALL SOUTH OF DANANG JUST AFTER TAU 12 AND DRAG
ACROSS RUGGED TERRAIN OF VIETNAM AND INTO CAMBODIA AND THAILAND.
THE FAVORABLE ENVIRONMENT WILL FUEL INTENSIFICATION TO A PEAK OF
35KTS BY TAU 12 PRIOR TO LANDFALL. AFTERWARD, LAND INTERACTION WILL
ERODE THE SYSTEM TO DISSIPATION BY TAU 36 AS IT REACHES VIETNAM. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT; HOWEVER,
GIVEN THE WEAK, ALBEIT FORMATIVE NATURE OF THE SYSTEM, THERE IS
ONLY MEDIUM CONFIDENCE IN THE JTWC TRACK AND INTENSITY FORECASTS. 

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