WDXS32 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (GEZANI) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.2S 52.1E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 265 NM EAST OF ANTANANARIVO, MADAGASCAR
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
RAPIDLY INTENSIFYING CYCLONE, WITH A SMALL EYE DEVELOPING DURING
THE PAST SIX HOURS IN CONVENTIONAL AND MICROWAVE IMAGERY. AN
INTERMITTENTLY BROKEN COLD RING OF -70 TO -80C CLOUD TOPS NOW
SURROUNDS A RAGGED, CLOUD-FILLED BUT WARMING EYE ABOUT 20 NM IN
DIAMETER. THE WIND FIELD REMAINS REMARKABLY COMPACT, WITH THE
ENTIRE GALE-FORCE WIND FIELD ESTIMATED TO BE CONTAINED WITHIN 70 NM
OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE STORM RESIDES IN A
HIGHLY FAVORABLE ENVIRONMENT WITH LIGHT VERTICAL SHEAR, WARM SEA
SURFACE TEMPERATURES, AND A COCOON OF DEEP MOISTURE. RADIAL
UPPER-LEVEL OUTFLOW IS OBSERVED IN ALL QUADRANTS, THOUGH RESTRICTED
TOWARDS THE NORTHEAST, WHICH IS THE UP-SHEAR DIRECTION. THE CURRENT
INTENSITY IS DIFFICULT TO ASSESS DURING THIS STAGE OF RAPID
INTENSIFICATION, BUT SUBJECTIVE AGENCY DVORAK ESTIMATES AND
OBJECTIVE SATELLITE-BASED ESTIMATES HAVE SPIKED IN RECENT HOURS.
THE INITIAL INTENSITY IS SET AT 90 KT, IN THE UPPER RANGE OF THESE
ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   CIMSS SATCON: 67 KTS AT 092203Z
   CIMSS ADT: 57 KTS AT 092100Z
   CIMSS AIDT: 54 KTS AT 092000Z
   CIMSS D-MINT: 79 KTS AT 092203Z
   CIMSS D-PRINT: 79 KTS AT 092230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE 21S (GEZANI) HAS JUST OVER 12
HOURS REMAINING BEFORE LANDFALL IN MADAGASCAR AS IT IS GUIDED
WESTWARD BY A SUBTROPICAL RIDGE TO THE SOUTH. GIVEN THE COMPACT AND
COMPLETE INNER CORE THAT HAS DEVELOPED, THE RAPID INTENSIFICATION
THAT IS ALREADY UNDERWAY MAY CONTINUE UNTIL LANDFALL. THE JTWC
FORECAST PRESUMES THIS WILL OCCUR, SHOWING A PEAK INTENSITY OF 110
KT IN 12 HOURS, SUPPORTED BY HAFS-A AND MULTIPLE STATISTICAL RAPID
INTENSITY AIDS. THERE IS ABOVE AVERAGE UNCERTAINTY IN THIS PEAK
INTENSITY VALUE, GIVEN THE RAPID STORM EVOLUTION THAT IS ONGOING.
MODEL GUIDANCE EXPECTS GEZANI TO CROSS MADAGASCAR IN ABOUT 24
HOURS, EMERGING IN THE MOZAMBIQUE CHANNEL BY TAU 48. WHILE THE
STORM WILL WEAKEN DRAMATICALLY OVER THE MOUNTAINS, THE CONCAVE
SHAPE OF THE COASTLINE NEAR THE EXIT POINT MAY FACILITATE QUICK
RECONSOLIDATION OF A COMPACT WIND FIELD AND REINTENSIFICATION OVER
THE CHANNEL, AIDED BY A LOW-SHEAR ENVIRONMENT. MODEL GUIDANCE IS IN
GOOD AGREEMENT ON THIS GENERAL EVOLUTION THROUGH 96 HOURS. DURING
THE 72-96 HOUR PERIOD, THE SUBTROPICAL STEERING RIDGE IS EXPECTED
TO SHIFT TO THE SOUTHEAST OF MADAGASCAR AND WEAKEN, CONCURRENT WITH
A LONGWAVE TROUGH DIGGING INTO SOUTH AFRICA, CAUSING 21S TO TURN
SOUTHWARD. THIS IS WHERE MODEL SPREAD BALLOONS, BASED MOSTLY ON
GEZANI'S LATITUDE. MORE SOUTHERLY TRACKS ACROSS THE CHANNEL RESULT
IN A STRAIGHT-FORWARD SOUTHWARD RECURVATURE, DEPICTED BY THE
MAJORITY OF MODELS. HOWEVER, SOME MODELS LIKE GFS, HAFS, AND
MINORITY ENSEMBLE CLUSTERS DEPICT A MORE NORTHERLY TRACK, CAUSING
THE LONGWAVE TROUGH TO MISS THE STORM, ALLOWING GEZANI TO CONTINUE
WESTWARD OR EVEN TURN NORTHWESTWARD INTO MOZAMBIQUE AS A RIDGE
REPLACES THE TROUGH OVER SOUTH AFRICA. THE JTWC FORECAST STICKS TO
THE RECURVATURE SCENARIO, BUT LOWER THAN AVERAGE TRACK FORECAST 
CONFIDENCE IN THE 72-120 HOUR PERIOD MAY PERSIST UNTIL 21S 
REESTABLISHES ON THE WESTERN SIDE OF MADAGASCAR.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS CLOSE TO THE
MULTI-MODEL CONSENSUS, LEANING TOWARDS A BLEND OF THE ECMWF, AIFS,
AND GOOGLE DEEPMIND ENSEMBLE MEAN. THE JTWC INTENSITY FORECAST IS
ABOVE THE MULTI-MODEL CONSENSUS THROUGH 12 HOURS, THEN NEAR THE
MULTI-MODEL CONSENSUS THROUGH 48 HOURS, AND THEN NEAR THE UPPER
EDGE OF THE MODEL INTENSITY ENVELOPE BEYOND 72 HOURS, PARTIALLY DUE
TO SOME MODELS MOVING INLAND OVER MOZAMBIQUE AND WEAKENING.

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