WDPN32 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (CHABA) 
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.3N 114.1E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 240 NM SOUTH OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS SPIRAL
BANDS OF FRAGMENTED, DEEP CONVECTION WRAPPING INTO AN ASSESSED LOW
LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON 302323Z SSMIS PASS, MULTI-AGENCY
FIXES AND OTHER SCATTEROMETRY DATA. THE INITIAL INTENSITY OF 50 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED
SCATTEROMETRY DATA, IMPROVING CONVECTIVE STRUCTURE, AND A
COMBINATION OF AGENCY AND AUTOMATED DVORAK ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 55 KTS AT 301803Z
   CIMSS ADT: 59 KTS AT 010140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS CHABA IS FORECAST TO TRACK NORTHWESTWARD
UNDER FAVORABLE ENVIRONMENTAL CONDITIONS BEFORE MAKING LANDFALL
EAST OF THE LUICHOW PENINSULA AFTER TAU 36. THE FAVORABLE
ENVIRONMENTAL CONDITIONS ARE CHARACTERIZED BY MODERATE DIVERGENCE
ALOFT, LOW VERTICAL WIND SHEAR (10-15 KTS), AND VERY WARM SEA
SURFACE TEMPERATURES (SST) (30-31C), WHICH WILL ALLOW CHABA TO
REACH A MAXIMUM INTENSITY OF 65 KNOTS BY TAU 24. IN ADDITION, THERE 
IS ALSO THE POSSIBILITY OF RAPID INTENSIFICATION BY TAU 24. ALSO BY 
TAU 24, TS CHABA WILL BEGIN TO INTERACT WITH BOTH THE ISLAND OF 
HAINAN AND EVENTUALLY MAINLAND CHINA SIGNIFICANTLY DEGRADING THE 
INTENSITY AS THE SYSTEM CONTINUES TO TRACK NORTHWESTWARD. BETWEEN TAU 
48 AND TAU 72 TS CHABA WILL MORE TRACK MORE NORTHWARD AS FALLS UNDER 
THE INFLUENCE OF A MAJOR LONGWAVE TROUGH AND BEGIN TO DISSIPATE DUE 
TO THE OROGRAPHIC IMPACTS OF SOUTHERN CHINA.

MODEL DISCUSSION: THE JTWC TRACK CONSENSUS MEMBERS ARE IN GOOD 
AGREEMENT WITH A 23 NM SPREAD BY TAU 12, GRADUALLY INCREASING TO 90 
NM SPREAD BY LANDFALL AT TAU 36. FOR THIS REASON, THE JTWC FORECAST 
TRACK IS PLACED WITH HIGH CONFIDENCE. RELIABLE INTENSITY GUIDANCE IS 
IN GOOD AGREEMENT WITH ALL MEMBERS SHOWING A STEADY INTENSIFICATION 
THROUGH TAU 36 AFTER WHICH LAND INTERACTION AND EVENTUAL LANDFALL 
OCCURS AND A SHARP DECREASE IN INTENSITY IS REFLECTED. MODEL GUIDANCE 
ALSO AGREES OF THE POSSIBILITY FOR RAPID INTENSIFICATION THROUGH TAUS 
24 THROUGH TAU 36.

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