WDPN32 PGTW 020900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 04W (CHABA) WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.2N 111.2E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 180 NM WEST-SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS SPIRAL BANDS
OF DEEP CONVECTION WRAPPING INTO A WELL DEFINED LOW LEVEL
CIRCULATION CENTER (LLCC). ANIMATED RADAR IMAGERY INDICATES THAT
DESPITE INCREASING LAND INTERACTION THE SYSTEMS STRUCTURE REMAINS
COHESIVE AND A DEFINED LLCC IS CLEARLY EVIDENT. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED RADAR
IMAGERY. THE INITIAL INTENSITY OF 70 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON AGENCY DVORAK INTENSITY ESTIMATES REFLECTING AN
EXPECTED DROP IN INTENSITY, WHILE CIMSS SATCON AND ADT REMAIN HIGH.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.5 - 77 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 80 KTS AT 020237Z
   CIMSS ADT: 84 KTS AT 020540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: LAND INTERACTION WITH SOUTHERN CHINA

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: TY 04W (CHABA) IS FORECAST TO MAKE LANDFALL
WITHIN THE HOUR JUST EAST OF ZHANJIANG, CHINA UNDER THE STEERING
INFLUENCE OF THE STR TO THE EAST. AS THE SYSTEM TRACKS INLAND ON A
NORTH-NORTHWESTWARD TRAJECTORY THROUGH TAU 24 THE SYSTEM IS
FORECAST TO RAPIDLY DECREASE IN INTENSITY DUE TO THE OROGRAPHIC
IMPACTS OF SOUTHERN CHINA. AS THE SYSTEM CONTINUES TO WEAKEN 04W
WILL TURN NORTH AND EVENTUALLY NORTH-NORTHEASTWARD BEFORE
DISSIPATING FULLY BY TAU 48.

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, NUMERICAL MODELS
ARE IN GOOD AGREEMENT THAT 04W WILL TRACK INLAND AND MAKE A GRADUAL
EASTWARD TURN BEFORE FULLY DISSIPATING. RELIABLE MODEL INTENSITY
GUIDANCE ALSO SHOWS GOOD AGREEMENT WITH ALL MEMBERS INDICATING A
SHARP DECLINE IN INTENSITY DUE TO LAND THROUGH TAU 24 AFTER WHICH A
MORE GRADUAL DECLINE UNTIL EVENTUAL DISSIPATION AT TAU 48. FOR
THESE REASONS JTWC TRACK AND INTENSITY FORECAST IS PLACED WITH
MEDIUM CONFIDENCE.

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