WDPN31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (SANBA) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.5N 108.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 158 NM SOUTHEAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS FLARING DEEP
CONVECTION THAT IS FULLY OBSCURING THE LOW LEVEL CIRCULATION CENTER
(LLCC) BENEATH. AN 182346Z GMI 89GHZ MICROWAVE IMAGE DEPICTS POORLY
ORGANIZED CENTRAL DEEP CONVECTION BEING SHEARED POLEWARD WHILE LOW
LEVEL CLOUD LINES TRACE A BROAD LLC IN THE PERIPHERY. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON MSI AND GMI
IMAGERY. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON A GENERAL AGREEMENT AMONGST AGENCY DVORAK
INTENSITY ESTIMATES OF 35KTS, WHILE CIMSS AUTOMATED INTENSITY
ESTIMATES INDICATE SLIGHTLY HIGHER.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
EAST-NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 45 KTS AT 181847Z
   CIMSS ADT: 51 KTS AT 182330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 16W (SANBA) IS FORECAST TO CONTINUE ITS
GENERALLY POLEWARD MARCH INTO THE GULF OF TONKIN UNDER THE STEERING
INFLUENCE OF THE STR TO THE EAST-NORTHEAST. NEAR TAU 24, AN
ADDITIONAL STR FORMS WEST OF THE SYSTEM, GENERALLY NEGATING FURTHER
POLEWARD MOVEMENT AND BRINGING ABOUT A QS PERIOD. GLOBAL MODELS
GENERALLY AGREE THAT THE RIDGING TO THE WEST AND EAST OF 16W JOIN
FORCES AND PUSH THE SYSTEM EQUATORWARD THROUGH THE REMAINING
FORECAST PERIOD. IN TERMS OF INTENSITY, NOW CLEAR OF HAINAN ISLAND
AND FUELED BY HIGH OHC VALUES, LOW VERTICAL WIND SHEAR (VWS) AND A
MOIST AIR COLUMN, 16W IS FORECAST TO GRADUALLY INTENSIFY TO 45KTS
BY TAU 36. AFTER REACHING ITS APOGEE, INCREASING VWS AND DRY AIR
ENTRAINMENT WILL STEADILY WEAKENING THE SYSTEM AS IT TRACKS
EQUATORWARD AND APPROACHES THE COAST OF TAIWAN, EVENTUALLY
DISSIPATING NEAR TAU 72.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT WITH ALL
MEMBERS INDICATING A SLOW TREK INTO THE GULF OF TONKIN THROUGH TAU
36, AFTER WHICH A SHARP EQUATORWARD TURN THROUGH DISSIPATION. DUE
TO MILD ALONG AND CROSS TRACK SPREADING, THE JTWC FORECAST TRACK IS
PLACED WITH MEDIUM CONFIDENCE. RELIABLE MODEL INTENSITY GUIDANCE IS
IN GOOD AGREEMENT WITH ALL MEMBERS INDICATING A GRADUAL
INTENSIFICATION TO 40-45KTS BY TAU 36 AND EVENTUAL DISSIPATION BY
TAU 72. FOR THIS REASON THE JTWC INTENSITY FORECAST IS PLACED WITH
HIGH CONFIDENCE. 

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