WDXS32 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (GEZANI) WARNING NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.3S 38.2E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 124 NM WEST-NORTHWEST OF EUROPA ISLAND
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 21S (GEZANI) WITH A CLOUD-FILLED EYE AND COLD CLOUD TOPS
CIRCLING THE CENTER. GEZANI HAD A PEAKED AT AROUND 1500Z BUT HAS
SINCE DEGRADED IN APPEARANCE OVER THE PAST 10 HOURS OR SO. SOME
ENHANCED WESTERLY VERTICAL WIND SHEAR APPEARS TO BE THE MAIN
CULPRIT FOR THE BRIEF DEGRADATION. THE SYSTEM ALSO TRACKED THROUGH
AN AREA OF LOW OCEAN HEAT CONTENT (OHC) VALUES, COINCIDING WITH THE 
STRUCTURAL WEAKENING. A 121552Z RCM-3 SAR IMAGE SHOWED A VMAX OF 97 
KTS, HOWEVER, THE APPEARANCE HAS WORSENED SINCE THE PASS, CAUSING THE
INITIAL INTENSITY ESTIMATE TO BE HELD STEADY AT 90 KTS WITH MEDIUM
CONFIDENCE. DVORAK CURRENT INTENSITY (CI) VALUES ALL AGREE ON T5.0,
SUPPORTING THE INITIAL INTENSITY ASSESSMENT. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE CLOUD-FILLED EYE IN
ANIMATED EIR IMAGERY WITH NO RECENT MICROWAVE IMAGERY TO ASSIST.
ENVIRONMENTAL ANALYSIS INDICATES THAT 21S IS IN A MARGINALLY
FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE RADIAL OUTFLOW
ALOFT, MODERATE (15-20 KTS) WESTERLY VERTICAL WIND SHEAR, AND WARM
(28-29 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   DEMS: T5.0 - 90 KTS
   FMEE: T5.0 - 90 KTS
   CIMSS ADT: 77 KTS AT 130000Z
   CIMSS D-PRINT: 88 KTS AT 130000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: POOL OF LOW OHC WATERS UNDERNEATH THE SYSTEM

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 21S IS FORECAST TO TRACK SOUTHWESTWARD,
ALONG THE NORTHWESTERN PERIPHERY OF THE STR THROUGH TAU 24. NEAR
TAU 24, 21S WILL BEGIN TO TURN SOUTHEASTWARD AS IT ATTEMPTS TO
ROUND THE RIDGE AXIS. HOWEVER, A MAJOR SHORTWAVE TROUGH IS EXPECTED
TO QUICKLY WEAKEN THE RIDGE AROUND TAU 48, WHILE A SEPARATE RIDGE
OVER SOUTHEASTERN AFRICA SIMULTANEOUSLY FORMS. THE FORMATION OF
THIS SECOND RIDGE WILL HINDER POLEWARD PROGRESSION, AND ULTIMATELY
PUSH 21S EASTWARD THROUGH TAU 72. MODELS HAVE COME INTO AGREEMENT
ON A TRACK THAT STAYS OFF THE COAST OF MOZAMBIQUE, CAUSING THE
TRACK NORTHWARD THROUGH THE CHANNEL TO BECOME MORE UNLIKELY. AFTER
TAU 72, A THIRD RIDGE TO THE EAST OF MADAGASCAR WILL BUILD AND
GUIDE 21S POLEWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD.
THERE REMAINS A CONSIDERABLE AMOUNT OF UNCERTAINTY REGARDING THE
TIMING OF THE FORMATION OF THE RIDGE EAST OF MADAGASCAR AND THE
INFLUENCE OF THE TROUGH THAT PASSES TO THE SOUTH. REGARDING
INTENSITY, 21S IS FORECAST TO CONTINUE INTENSIFYING THROUGH TAU 24
TO A PEAK OF AROUND 105 KTS DUE TO LESSENING SHEAR AND INCREASING
OHC. AFTER TAU 24, INCREASING WESTERLY SHEAR INDUCED BY THE
INCOMING TROUGH WILL WEAKEN THE VORTEX THROUGH TAU 96. AFTER TAU
96, 21S WILL BEGIN TO ENTER COOLER WATERS, WHICH WILL FURTHER
WEAKEN THE SYSTEM. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE, THOUGH IN BETTER
AGREEMENT, STILL REMAINS IN VERY POOR AGREEMENT AFTER TAU 48.
THROUGH TAU 48, THERE IS A CROSS-TRACK SPREAD OF 115 NM AND AN
ALONG-TRACK SPREAD OF 190 NM. AT TAU 120 ALONG-TRACK SPREAD
INCREASES TO OVER 700 NM. ECMWF HAS STOPPED SHOWING THE SHARP TURN
BACK THROUGH THE MOZAMBIQUE CHANNEL, CAUSING CONFIDENCE TO BE
SLIGHTLY HIGHER COMPARED TO THE PREVIOUS FORECAST, BUT IT REMAINS
THE SLOWEST AND NORTHERNMOST MODEL. GFS CONTINUES TO BE THE
FASTEST MODEL AND SHOWS A FAST TRACK STRAIGHT SOUTHEASTWARD. AI
MODELS ARE NOW CLOSELY ALIGNED, AND THE JTWC TRACK FORECAST FOLLOWS
MORE CLOSELY TO THOSE SOLUTIONS AFTER TAU 48. INTENSITY GUIDANCE
(WITH THE EXCEPTION OF GFS) AGREES ON INTENSIFICATION THROUGH TAU
24 BEFORE STEADY WEAKENING. PEAK INTENSITIES RANGE FROM 95-110 KTS
WITH HAFS-A BEING THE MOST AGGRESSIVE MODEL. THE JTWC INTENSITY
FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS THROUGHOUT
THE FORECAST PERIOD WITH OVERALL MEDIUM CONFIDENCE.

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