WDPN31 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.0N 113.2E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 383 NM EAST OF HO CHI MINH CITY, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING SYSTEM, WITH IMPROVED DEEP CONVECTIVE BANDING WRAPPING 
FROM THE NORTHERN QUADRANT INTO THE SOUTHERN QUADRANT OF AN IMPROVED 
LOW-LEVEL CIRCULATION CENTER (LLCC). TROPICAL DEPRESSION 28W HAS 
FORMED SLOWLY WITHIN A COMPLEX, LATE SEASON ENVIRONMENT, ADJACENT TO 
A STRONG NORTHEAST SURGE EVENT AND EXTENSIVE SWATH OF 25-30 KNOT 
NORTH-NORTHEASTERLY TO NORTHERLY WINDS. INVEST 98W, WHICH FORMED IN 
CLOSE PROXIMITY TO THIS SYSTEM, IS WEAKENING RAPIDLY AND GETTING 
ABSORBED INTO THE SOUTHEAST PERIPHERY OF 28W. THE INITIAL POSITION IS 
PLACED WITH MEDIUM CONFIDENCE BASED ON EIR IMAGERY. THE INITIAL 
INTENSITY OF 25 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE 
AGENCY DVORAK ESTIMATES AND THE CIMSS D-PRINT ESTIMATE OF 27 KNOTS.

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

CURRENT STEERING MECHANISM: LOW-LEVEL SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   CIMSS D-PRINT: 27 KTS AT 221200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 28W IS TRACKING ALONG
THE SOUTHWESTERN PERIPHERY OF THE LOW-LEVEL STR AND IS FORECAST TO
CONTINUE TRACKING NORTHWESTWARD THROUGH TAU 24. MODEST 
INTENSIFICATION IS ANTICIPATED THROUGH TAU 24, WITH A PEAK INTENSITY 
OF 40 KNOTS FORECAST BY TAU 24 DUE TO MARGINALLY FAVORABLE 
CONDITIONS. AFTER TAU 24, THE SYSTEM WILL SLOW AS IT ENCOUNTERS 
STRONG LOW-LEVEL SURGE FLOW THEN WILL TURN SHARPLY WEST-SOUTHWESTWARD 
WHILE WEAKENING DUE TO SLIGHTLY COOLER SST VALUES (25-26C) AND 
INFUSION OF COOLER, MORE STABLE AIR ASSOCIATED WITH THE SURGE EVENT. 
AFTER TAU 48, THE SURGE EVENT WILL GRADUALLY WEAKEN ALLOWING THE 
SYSTEM TO TRACK WEST-SOUTHWESTWARD INTO SOUTHERN VIETNAM UNDER THE 
LOW-LEVEL RIDGE OVER SOUTHEAST ASIA. TD 28W WILL QUICKLY DISSIPATE 
OVER VIETNAM BY TAU 72 DUE TO LAND INTERACTION.      

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT WITH 
DETERMINISTIC TRACKERS INDICATING A WESTWARD TO SOUTH-SOUTHWESTWARD 
TRACK. THE 220000Z GFS ENSEMBLE (GEFS) SHOWS A SIMILAR SPREAD OF 
SOLUTIONS, WITH THE BULK OF THE SOLUTIONS TRACKING THE DISSIPATING 
SYSTEM JUST SOUTH OF VIETNAM. THE 220000Z ECMWF ENSEMBLE (EPS) 
SUPPORTS A MORE WESTWARD TO WEST-SOUTHWESTWARD TRACK INTO SOUTHERN 
VIETNAM. WITH THE EXCEPTION OF HAFS-A, RELIABLE INTENSITY GUIDANCE 
SUPPORTS THE JTWC INTENSITY FORECAST WITH MEDIUM CONFIDENCE.      

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