WDXS31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04S (FOUR)       
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.5S 91.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 1139 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 04S IS LOCATED WITHIN A MARGINAL ENVIRONMENT WITH PERSISTENT,
MODERATE NORTHEASTERLY FLOW AND SIGNIFICANT DRY AIR ENTRAINMENT
THROUGH THE MID- TO UPPER-LEVELS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY DEPICTS AN EXPOSED, WELL-DEFINED LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH RAPIDLY DISSIPATING DEEP CONVECTION
SHEARED OVER THE SOUTHWEST QUADRANT. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE EIR IMAGERY. A 041925Z GMI 89GHZ
COLOR COMPOSITE MICROWAVE IMAGE REVEALS SHALLOW BANDING WRAPPING
INTO A DEFINED LLCC WITH ISOLATED BURSTS OF CONVECTION DISPLACED
OVER 200NM TO THE SOUTH. A RECENT SCATTEROMETER IMAGE SHOWS A PATCH
OF 30-35 KNOT WINDS OVER THE SOUTHEAST QUADRANT WITH LESS THAN 30
KNOT WINDS ELSEWHERE. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THIS DATA.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 41 KTS AT 041410Z
   CIMSS ADT: 34 KTS AT 041740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: ADJUSTED THE INTENSITY FORECAST WITH
A DISSIPATION SCENARIO AND REDUCED THE FORECAST DURATION TO 72
HOURS.

FORECAST DISCUSSION: TC 04S IS STRUGGLING UNDER MARGINAL CONDITIONS
AND IS EXPECTED TO CONTINUE TO STRUGGLE OVER THE NEXT THREE DAYS AS
IT TRACKS WEST-SOUTHWESTWARD TO WESTWARD. PERSISTENT NORTHEASTERLY
VERTICAL WIND SHEAR (VWS) AND DRY AIR ENTRAINMENT WILL CONTINUE TO
HINDER DEVELOPMENT THROUGH THE NEXT 36 TO 48 HOURS. AFTER THIS
PERIOD, VWS WILL DECREASE HOWEVER THE ENVIRONMENT WILL BECOME
INCREASINGLY DRIER WITH WEAK BAROCLINICITY ASSOCIATED WITH THE
INFUSION OF COOLER, MORE STABLE AIR. THEREFORE, TC 04S IS NOW
FORECAST TO DISSIPATE BY TAU 72 OR PERHAPS SOONER AS INDICATED IN
THE LATEST GFS RUN.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
SUPPORTING THE JTWC FORECAST TRACK WITH HIGH CONFIDENCE. THE JTWC
INTENSITY FORECAST IS MORE UNCERTAIN WITH THE POTENTIAL FOR
DISSIPATION WITHIN THE NEXT 36 TO 48 HOURS.

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