WDXS32 PGTW 110300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (GEZANI) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.2S 48.3E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 62 NM NORTHEAST OF ANTANANARIVO,
MADAGASCAR
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: XX FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 21S (GEZANI) WITH INCREASINGLY DISORGANIZED CONVECTIVE
STRUCTURES WRAPPING AROUND THE LOW-LEVEL CIRCULATION CENTER (LLCC)
AS THE SYSTEM TRACKS WESTWARD ACROSS MADAGASCARS ANKARATRA MASSIF.
TC 21S MADE LANDFALL AROUND 101800Z, WHERE ITS ONCE WELL-DEFINED
EYE-FEATURE QUICKLY COLLAPSED DUE TO TOPOGRAPHICAL INTERACTION. THE
ENVIRONMENT HAS BECOME MARGINAL SINCE THE PREVIOUS WARNING, WITH
LOW VERTICAL WIND SHEAR (VWS) OF LESS THAN 10 KTS, SUPPORTIVE
UPPER-LEVEL POLEWARD OUTFLOW, AND PERSISTENT INTERACTION WITH
MADAGASCARS RUGGED TERRAIN. THE INITIAL POSITION HAS BEEN PLACED
WITH MEDIUM CONFIDENCE BASED ON ANIMATED MSI IMAGERY. THE INITIAL
INTENSITY HAS BEEN ASSESSED WITH MEDIUM CONFIDENCE BASED ON
STATISTICAL DYNAMICAL MODEL DATA. OVER THE LAST FEW HOURS, TC 21S
HAS RAPIDLY WEAKENED AS THE LOW-LEVEL VORTEX CONTINUES TO DECOUPLE
FROM THE SYSTEMS UPPER-LEVEL SUPPORT STRUCTURE.

INITIAL WIND RADII BASIS: WIND RADII VALID OVER OPEN WATER ONLY

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: OVER LAND
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE TRACK FORECAST DURING THE LATER
TAUS HAS STARTED TO SLOW AND TRACK GENERALLY EASTWARD INTO THE END
OF THE FORECAST PERIOD.

FORECAST DISCUSSION: TC 21S IS FORECASTED TO TRACK
WEST-SOUTHWESTWARD THROUGH CENTRAL MADAGASCAR OVER THE NEXT 18
HOURS ALONG THE NORTHWEST EXTENT OF THE STR CENTERED TO THE
SOUTHEAST. AS THE SYSTEM RE-EMERGES OVER OPEN WATER, THE CYCLONE
WILL CONTINUE SOUTHWESTWARD TOWARD THE STR AXIS NEAR TAU 72.
FOLLOWING TAU 72, TC 21S WILL BEGIN ROUNDING THE WESTERN PERIPHERY
OF THE STR AXIS AS THE TRACK BECOMES GENERALLY SOUTHWARD FOR 24
HOURS UNTIL TAU 92. TC GEZANI IS THEN FORECASTED TO ENTER A PERIOD
OF COMPETING STEERING MECHANISMS, WITH AN UPPER-LEVEL CUT-OFF LOW
JUST EAST OF MADAGASCAR ADDING A SOUTHERLY CHANNEL OF GRADIENT
WINDS THROUGH THE MID-LEVELS, DRIVING THE CYCLONE EASTWARD INTO TAU
120 AS THE ASSOCIATED HEIGHT GRADIENT TIGHTENS AGAINST A
DEEP-LAYER STR CENTERED TO THE WEST OVER SOUTHERN AFRICA. REGARDING 
INTENSITY, TC 21S IS FORECASTED TO CONTINUE RAPIDLY WEAKENING OVER THE 
NEXT 12-18 HOURS DUE TO PERSISTENT FRICTIONAL INFLUENCES AS THE 
CYCLONE 
TRACKS THROUGH CENTRAL MADAGASCAR. AS THE CYCLONE RE-EMERGES OVER OPEN
WATER BETWEEN TAU 12 AND TAU 18, TC GEZANI IS FORECASTED TO BEGIN
GRADUALLY INTENSIFYING THROUGH A FAVORABLE ENVIRONMENT, WITH LOW VWS,
WARM SEA SURFACE TEMPERATURES, AND SUPPORTIVE OUTFLOW ALOFT. AS THE
CYCLONE BEGINS ROUNDING THE STR AXIS, CONTINUED INTENSIFICATION TO
80 KTS IS FORECASTED WITH ENHANCED UPPER-LEVEL DUAL-CHANNEL
OUTFLOW. FOLLOWING TAU 72, VWS IS FORECASTED TO BEGIN INCREASING TO
MORE THAN 15 KTS AS SEA SURFACE TEMPERATURES BEGIN TO COOL,
INITIATING A SLIGHT WEAKENING TREND TO 65 KTS BETWEEN TAU 96 AND
TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE AND ARTIFICIAL
INTELLIGENCE (AI) GUIDANCE REMAIN IN VERY TIGHT AGREEMENT THROUGH
THE INITIAL 72 HOURS OF THE FORECAST PERIOD, WITH A CROSS-TRACK
SPREAD OF JUST 77 NM. FOLLOWING TAU 72, NUMERICAL MODEL AND AI
SOLUTIONS BEGIN TO DIVERGE, INDICATING A POTENTIAL BIFURCATION
TREND DUE TO UNCERTAINTIES IN THE COMPETING STEERING MECHANISMS
BETWEEN TAU 72 AND TAU 120. THE CROSS-TRACK SPREAD INCREASES
SIGNIFICANTLY BETWEEN TAU 96 AND TAU 120, WITH THE BULK OF GUIDANCE
SHOWING AN EASTWARD TRACK UNTIL THE END OF THE FORECAST PERIOD. A
FEW OUTLIERS REMAIN, WITH NAVGEM INDICATING A WESTWARD TRACK INTO
MOZAMBIQUE AFTER TAU 96 AND THE UKMET DETERMINISTIC SOLUTION
SHOWING POLEWARD PROGRESSION AFTER TAU 72. THE JTWC TRACK FORECAST
HAS BEEN PLACED WITH HIGH CONFIDENCE AND NEAR THE JTWC MULTI-MODEL 
CONSENSUS UNTIL TAU 72, AND LOW CONFIDENCE THEREAFTER DUE TO 
UNCERTAINTIES IN THE AFOREMENTIONED STEERING FLOW. REGARDING 
INTENSITY, THE JTWC INTENSITY FORECAST HAS BEEN ASSESSED WITH MEDIUM 
CONFIDENCE THROUGHOUT THE FORECAST PERIOD AS THE BULK OF THE JTWC 
MULTI-MODEL CONSENSUS GUIDANCE CHARACTERIZES GRADUAL INTENSIFICATION 
AS THE SYSTEM RE-EMERGES OVER WATER, WITH A STEADY WEAKENING TREND 
BETWEEN TAU 72 AND TAU 120. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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