WDXS31 PGTW 250900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04S (CHENGE) WARNING 
NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 7.8S 51.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 706 NM NORTH-NORTHEAST OF ANTANANARIVO,
MADAGASCAR
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 04S (CHENGE) IS BEING HEAVILY SHEARED WITH
ASSOCIATED CONVECTION DISPLACED TO THE SOUTHWEST AS DEPICTED IN
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY. ENVIRONMENTAL
CONDITIONS REMAIN UNFAVORABLE WITH HIGH VERTICAL WIND SHEAR (25-30
KTS), SEA SURFACE TEMPERATURES OF 26 C TO 27 C, AND MODERATE
EQUATORWARD OUTFLOW. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON A 250612Z METOP-B ASCAT DATA AND A 250204Z
RCM-3 SAR PASS. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE AFOREMENTIONED ASCAT AND SAR PASSES.

INITIAL WIND RADII BASIS: 250204Z RCM-3 SAR DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS ADT: 49 KTS AT 250300Z
   CIMSS AIDT: 43 KTS AT 250500Z
   CIMSS D-MINT: 31 KTS AT 250200Z
   CIMSS D-PRINT: 30 KTS AT 250500Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS CHENGE WILL REMAIN ON A WEST-NORTHWESTWARD
TRACK FOR THE REMAINDER OF THE FORECAST PERIOD UNDER THE INFLUENCE
OF A SUBTROPICAL RIDGE TO THE SOUTH. LITTLE CHANGE IS EXPECTED IN
THE CIRCULATION TILL AFTER TAU 12 AT WHICH TIME PROLONGED EXPOSURE
TO HIGH WIND SHEAR WILL START TO WEAKEN TS CHENGE BELOW TROPICAL
STORM INTENSITY. BY TAU 36 TS CHENGE WILL HAVE FULLY DISSIPATED
OVER WATER.

MODEL DISCUSSION: CROSS TRACK SPREAD IS UNDER 45 NM FOR THE ENTIRE
FORECAST PERIOD SIGNIFYING GOOD CONSENSUS BETWEEN THE MODELS. THE
OFFICIAL JTWC TRACK IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS
WITH HIGH CONFIDENCE. THE INTENSITY SPREAD IS AROUND 10 KNOTS WITH
HAFS-A DROPPING THE STORM BELOW WARNING CRITERIA BEFORE THE REST OF
THE GUIDANCE. THE OFFICIAL JTWC INTENSITY FORECAST REFLECTS THE
MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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