WDXS31 PGTW 191500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (EMNATI) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.4S 58.1E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 227 NM NORTH-NORTHEAST OF PORT LOUIS,
MAURITIUS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
OVER THE PAST SIX TO TWELVE HOURS ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY HAS SHOWN BRIEF PERIODS WHEN AN WEAK EYE FEATURE
ATTEMPTED TO FORM, BUT WAS UNABLE TO SUSTAIN ITSELF. AT PRESENT,
THE CORE CIRCULATION IS NOT CLEARLY EVIDENT IN THE EIR, WITH DEEP
CONVECTION LIMITED TO A SMALL REGION NORTHWEST OF THE ASSESSED
CENTER.  LATE RECEIPT OF A 191254Z SSMIS PASS SHOWED THAT THE LOW
LEVEL CIRCULATION CENTER (LLCC) AS DEPICTED IN THE 37GHZ BAND IS
DISPLACED UPSHEAR (EAST) OF THE UPPER-LEVEL EYE FEATURE, AND
PROVIDED HIGH CONFIDENCE TO THE INITIAL POSITION. THE MICROWAVE
IMAGERY ALSO SHOWS AN IRREGULAR INNER EYEWALL, BROKEN ON THE
EASTERN SIDE, WITH HINTS OF A MUCH BROADER SECONDARY EYEWALL
BEGINNING TO FORM, WRAPPING IN TOWARDS THE CENTER IN A BROAD ARC
ACROSS THE NORTHERN SIDE OF THE SYSTEM. THE INITIAL INTENSITY OF 70
KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED, SLIGHTLY LOWER THAN
THE AGENCY DVORAK ESTIMATES IN LIGHT OF THE SIGNIFICANTLY LOWER ADT
ESTIMATE AND EXTRAPOLATION OF A 190137Z SENTINEL-1A SAR BULLSEYE
PASS. ANALYSIS REVEALS AN OVERALL FAVORABLE ENVIRONMENT, WITH
RELATIVELY LOW SHEAR AND GOOD OUTFLOW BEING OFFSET BY LOW OCEAN
HEAT CONTENT DUE TO UPWELLING EXACERBATING THE ALREADY COOLER
WATERS IN THE WAKE OF PREVIOUS CYCLONES TRANSITING THE REGION.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHWEST PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   FMEE: T4.5 - 77 KTS
   FIMP: T4.5 - 77 KTS
   CIMSS SATCON: 86 KTS AT 190943Z
   CIMSS ADT: 63 KTS AT 191215Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: SIGNIFICANT UPWELLING OF COOLER WATERS.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: OVER THE NEXT 12 TO 24 HOURS TC 13S IS
EXPECTED TO TRACK SOUTHWESTWARD ALONG THE NORTHWEST SIDE OF THE STR
TO THE SOUTHEAST. A SECONDARY RIDGE DEVELOPS TO THE SOUTHEAST OF
MADAGASCAR BY TAU 12 AND QUICKLY SLIDES BY TO THE SOUTH, ALLOWING
FOR A SLIGHT FLATTENING OUT OF THE TRACK THROUGH TAU 36. THIS NEW
RIDGE MOVES TO A POSITION TO THE SOUTHEAST OF THE SYSTEM AND
BECOMES THE DOMINATE STEERING MECHANISM BY TAU 48 AND THE TC WILL
SHIFT ONCE AGAIN TO A MORE SOUTHWESTWARD TRACK THROUGH THE
REMAINDER OF THE FORECAST PERIOD. THE SYSTEM IS EXPECTED TO MAKE
LANDFALL ALONG THE COAST OF SOUTH-CENTRAL MADAGASCAR AT OR NEAR TAU
72, QUICKLY CROSS THE ISLAND AND REEMERGE OVER WATER BY TAU 120.
OVERALL THE ENVIRONMENT IS FAVORABLE FOR INTENSIFICATION WITH GOOD
OUTFLOW AND LOW SHEAR, THOUGH THE RATE OF INTENSIFICATION WILL BE
LIMITED FIRST BY THE CONTINUED UPWELLING OF COOLER WATERS AND
SECOND BY THE POSSIBILITY OF AN EYEWALL REPLACEMENT CYCLE (ERC) AS
THE SYSTEM CONTINUES TO INTENSIFY. THE SYSTEM IS STILL FORECAST TO
PEAK AT 95 KNOTS BY TAU 48, WITH SLIGHT WEAKENING EXPECTED PRIOR TO
LANDFALL AS THE SYSTEM MOVES OVER COOLER SSTS ALONG THE COAST AND
ENTRAINS SOME DRY AIR FROM THE ISLAND. ONCE OVER LAND THE SYSTEM
WILL RAPIDLY WEAKEN DUE TO INTERACTION WITH THE RUGGED TERRAIN OF
MADAGASCAR, DOWN TO A MINIMUM NEAR 45 KNOTS. ONCE THE SYSTEM MOVES
BACK OVER WATER IT IS EXPECTED TO BEGIN TO REINTENSIFY. HOWEVER, BY
TAU 120 TC 13S WILL BEGIN TO TRANSITION TO A SUBTROPICAL CYCLONE AS
IT CROSSES THE 26C ISOTHERM.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT ONLY THROUGH
TAU 12, WITH A SIGNIFICANT DELTA BETWEEN THE GFS AND NAVGEM
SOLUTIONS AND THE REMAINDER OF THE GUIDANCE PACKAGE THEREAFTER.
WHILE SPREAD IN THE ENVELOPE HAS DECREASED SINCE THE LAST RUN, THE
NAVGEM HAVING MOVED CLOSER TO THE OTHER MEMBERS, IT STILL REMAINS
ABOVE 390NM BY TAU 120, WITH GFS AND NAVGEM ON THE POLEWARD SIDE
AND ECMWF MARKING THE EQUATORWARD BOUNDARY. THE JTWC FORECAST IS
SHIFTED SOUTHWARD FROM THE PREVIOUS FORECAST, AND HUGS THE SOUTHERN
SIDE OF THE MAIN GROUPING OF MODEL TRACKERS WITH MEDIUM CONFIDENCE
THROUGH TAU 48 AND LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE IS
IN FAIRLY GOOD AGREEMENT THROUGH LANDFALL WITH A TIGHT 10 KNOT
ENVELOPE THROUGH TAU 72. AFTER LANDFALL MODELS DIVERGE WITH THE
JTWC FORECAST HEDGED TOWARD THE MESOSCALE COUPLED MODELS, WHICH
SHOW MAJOR WEAKENING THEN REINTENSIFICATION AFTER EMERGENCE OVER
WATER. CONFIDENCE IS MEDIUM THROUGH LANDFALL AND LOW THEREAFTER. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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