WDXS32 PGTW 160900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (GEZANI) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.9S 41.9E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 187 NM SOUTH-SOUTHEAST OF EUROPA ISLAND
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) IMAGERY REVEALS A LOW-LEVEL
CIRCULATION CENTER (LLCC) NEARLY FULLY OBSCURED BY A RECENTLY
DEVELOPED CENTRAL DENSE OVERCAST (CDO) ASSOCIATED WITH TROPICAL
CYCLONE (TC) 21S (GEZANI). HIGH (25+ KTS) NORTHEASTERLY VERTICAL
WIND SHEAR (VWS) IS BECOMING INCREASINGLY MORE APPARENT AS THE
DEEP-CONVECTION IS BEING COMPLETELY SHEARED OFF TO THE SOUTHEAST. 
COLD-AIR STRATOCUMULUS BANDING CAN BE SEEN THROUGHOUT THE WESTERN AND
NORTHERN QUADRANTS INDICATING PERSISTENT DRY AIR INTRUSION. THE
OTHERWISE UNFAVORABLE ENVIRONMENTAL CHARACTERISTICS ARE CURRENTLY
OFFSET BY STRONG POLEWARD OUTFLOW AND WARM (28-29 C) SEA SURFACE
TEMPERATURES, RESULTING IN OVERALL MARGINALLY UNFAVORABLE CONDITIONS 
FOR STRENGTHENING AND RE-DEVELOPMENT. A HIGH-CONFIDENCE INITIAL 
POSITION IS PREDICATED UTILIZING A 160528Z METOP-B ASCAT PASS, WHILE 
THE INITIAL INTENSITY OF 75 KTS IS ASSESSED WITH MEDIUM CONFIDENCE,
FUSING AVAILABLE AGENCY DVORAK, OBJECTIVE ESTIMATES LISTED BELOW,
AND AN EARLIER 160224Z RCM-1 SAR PASS.

INITIAL WIND RADII BASIS: 160528Z METOP-B ASCAT PASS

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE EAST WITH RESIDUAL INFLUENCE FROM A PASSING
LONG-WAVE TROUGH POSITIONED TO THE SOUTHEAST AND PASSING EASTWARD

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   CIMSS SATCON: 57 KTS AT 160351Z
   CIMSS ADT: 57 KTS AT 160300Z
   CIMSS AIDT: 56 KTS AT 160500Z
   CIMSS D-MINT: 54 KTS AT 160350Z
   CIMSS D-PRINT: 61 KTS AT 160530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR INTRUSION EVIDENT OVER THE WESTERN
SEMICIRCLE

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: AS THE EASTWARD-PROPAGATING BAROCLINIC TROUGH
IS MOVING AWAY FROM TC 21S, A STRENGTHENING DEEP-LAYER STR CENTERED TO 
THE EAST IS FORECAST TO ESTABLISH ITSELF AS THE PRIMARY STEERING 
MECHANISM FOR THE SYSTEM. SIMULTANEOUSLY, HIGH AND INCREASING VWS IS 
EXPECTED TO DECOUPLE MOST OF THE REMAINING DEEP-LAYER CONVECTION OVER 
THE NEXT 12 HOURS, RESULTING IN TC GEZANI BECOMING INCREASINGLY MORE 
SHALLOW, WHILE RECURVING POLEWARD. OVER THE NEXT 24 HOURS, THE SEA 
SURFACE TEMPERATURES WILL REMAIN WARM AND POLEWARD OUTFLOW CHANNEL IS 
EXPECTED TO REMAIN IN PLACE, RESULTING IN ONLY SLIGHT WEAKENING. 
ADDITIONALLY, DURING THIS TIMEFRAME, TC 21S IS EXPECTED TO BE ABLE TO 
SHIELD ITS CIRCULATION FROM OTHERWISE PERSISTENT DRY AIR INTRUSION. 
HOWEVER, AS THE SYSTEM ACCELERATES AND HEADS FURTHER SOUTHWARD, THE 
SSTS WILL RAPIDLY COOL AND EXTRATROPICAL TRANSITION (ETT) WILL BEGIN 
AS SOON AS TAU 36. THE FULL TRANSFORMATION INTO A COLD-CORE SYSTEM IS 
EXPECTED TO BE COMPLETE BY TAU 48, WITH THE PEAK INTENSITY DROPPING TO 
50-55 KTS.

MODEL DISCUSSION: CONFIDENCE IN THE OVERALL TRACK FORECAST IS GOOD,
AS ALL MODELS INDICATE IMMINENT POLEWARD TURN. RESIDUAL UNCERTAINTY
IS PRIMARILY ATTRIBUTED TO CROSS-TRACK DISPERSION OF APPROXIMATELY
115 NM NEAR THE TAU 24 FORECAST POINT, DRIVEN BY THE WESTERNMOST
POSITIONS PREDICTED BY NAVGEM. OTHERWISE, THE ENVELOPE SPREAD REMAINS
WITHIN 60 NM THROUGHOUT THE FORECAST PERIOD. THE OFFICIAL JTWC
FORECAST IS LAID IN CLOSE PROXIMITY TO THE MULTI-MODEL CONSENSUS MEAN,
WITH A MINOR DEVIATION TO ACCOUNT FOR THE ANOMALOUS NAVGEM SOLUTION. 
THE INTENSITY GUIDANCE IS IN STRONG AGREEMENT, UNANIMOUSLY PROJECTING 
A STEADY WEAKENING TREND, BRIEFLY PAUSED BETWEEN TAUS 24 AND 36, AS 
REFLECTED IN THE FORECAST. CONSEQUENTLY, THE JTWC INTENSITY ASSESSMENT 
IS POSITIONED IN CLOSE PROXIMITY TO THE MULTI-MODEL CONSENSUS WITH
HIGH CONFIDENCE.

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