WDXS32 PGTW 150300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (GEZANI) WARNING 
NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.7S 38.6E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 284 NM SOUTH-SOUTHWEST OF EUROPA ISLAND
   MOVEMENT PAST 6 HOURS: EASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
THE STRUCTURE OF TROPICAL CYCLONE (TC) 21S (GEZANI) CONTINUES TO
STEADILY DETERIORATE AS DRY AIR ENTRAINMENT ERODES CONVECTIVE
BANDING AROUND THE LOW LEVEL CIRCULATION CENTER (LLCC), AS DEPICTED
BY ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY.
ENVIRONMENTAL CONDITIONS HAVE REMAINED MARGINAL OVER THE LAST FEW
HOURS, AS INCREASING DRY-AIR ENTRAINMENT AND VERTICAL WIND SHEAR
(VWS) APPROACHING 20 KTS COMPETES WITH WARM SEA SURFACE
TEMPERATURES BETWEEN 27-28 C AND SUPPORTIVE RADIAL OUTFLOW ALOFT.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
ANIMATED EIR AND A 150024Z GPM GMI 89 GHZ IMAGE. THE INITIAL
INTENSITY OF 85 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON A
141607Z RCM-3 SAR PASS.

INITIAL WIND RADII BASIS: 141607Z RCM-3 SAR DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTHEAST, INTERRUPTED BY A PASSING LONG-WAVE
BAROCLINIC TROUGH TO THE SOUTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   FMEE: T4.5 - 77 KTS
   CIMSS SATCON: 65 KTS AT 150030Z
   CIMSS ADT: 61 KTS AT 150030Z
   CIMSS AIDT: 77 KTS AT 150030Z
   CIMSS D-MINT: 60 KTS AT 150022Z
   CIMSS D-PRINT: 69 KTS AT 150030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK RADIAL
   OTHER FACTORS: DRY AIR SURROUNDING THE SYSTEM

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: TC 21S IS NOW TRACKING EASTWARD DUE TO
INTERACTION WITH THE DEEP-LAYER LONG-WAVE BAROCLINIC TROUGH TO THE
SOUTHWEST. THE SYSTEM IS FORECASTED TO CONTINUE EASTWARD OVER THE
NEXT 36 HOURS WHILE STEADILY WEAKENING FROM A PROLONGED BATTLE WITH
DRY AIR PRESSURING THE VORTEX FROM THE WEST AND INCREASING VWS (30+
KTS). FOLLOWING TAU 36, THE SUBTROPICAL RIDGE EAST OF MADAGASCAR
WILL RESUME STEERING THE CYCLONE, DRIVING THE VORTEX SOUTHWARD OVER
COOLER SEA SURFACE TEMPERATURES, CONTRIBUTING TO A SHALLOWING OUT
OF THE CIRCULATION. FOLLOWING TAU 36, AN EXTENSION OF THE STR TO THE 
EAST WILL BUILD SLIGHTLY SOUTHWESTWARD, SLOWING POLEWARD PROGRESSION 
BETWEEN UNTIL TAU 48. REGARDING INTENSITY, TC 21S IS EXPECTED TO
RAPIDLY DECAY TOWARD 55 KTS BY TAU 72 AS THE ENVIRONMENT BECOMES
INCREASINGLY UNFAVORABLE. NEAR TAU 48, THE SYSTEM IS FORECASTED TO
BEGIN EXTRATROPICAL TRANSITION AS IT BECOMES TRACKS CLOSER TO THE
THE MID-LATITUDE WESTERLIES TO THE SOUTH, WHILE FULLY COMPLETING
EXTRATROPICAL TRANSITION BY THE END OF THE FORECAST PERIOD. 

MODEL DISCUSSION: MODEL GUIDANCE HAS SHIFTED EASTWARD WITH THE
TRACK OF THE SYSTEM. CROSS TRACK SPREAD AMONGST THE GUIDANCE IS
SPREAD UP TO 180 NM DUE TO VARYING DEGREES OF SHARPNESS IN REGARDS
TO THE SOUTHWARD PUSH OF TC 21S AS THE STR EAST OF MADAGASCAR
RESUMES STEERING. THE JTWC FORECASTED TRACK LIES BETWEEN THE MULTI
MODEL CONSENSUS AND AI SOLUTIONS WITH MEDIUM CONFIDENCE. INTENSITY
GUIDANCE IS SPREAD UP TO 25 KTS AT TAU 24. THE MAJORITY OF THE
GUIDANCE AGREES ON THE STEADY WEAKENING OF THE SYSTEM AS THE
ENVIRONMENT BECOMES INCREASINGLY UNFAVORABLE. THE JTWC FORECASTED
INTENSITY LIES JUST BELOW THE MULTI MODEL CONSENSUS, ACCOUNTING FOR
THE FORECASTED INCREASED VWS AND DRY-AIR ENTRAINMENT WITH MEDIUM
CONFIDENCE. 

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