WDXS31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (EMNATI) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.9S 64.2E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 543 NM NORTHEAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS
FURTHER CONSOLIDATED AS THE CENTRAL CONVECTION SIGNIFICANTLY
DEEPENED AND BECOME MORE SYMMETRICAL OVER THE LAST 12 HRS. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE USING LOW CLOUD
TRACING AND EXTRAPOLATION FROM SHALLOW RAIN BANDS SPIRALING INTO AN
OBSCURED LOW LEVEL CIRCULATION IN THE 170908Z AMSR2 89GHZ MICROWAVE
IMAGE. THE INITIAL INTENSITY OF 55KTS IS BASED ON AN OVERALL
ASSESSMENT OF AGENCY AND AUTOMATED DVORAK ESTIMATES (SEE BELOW) AND
REFLECTS THE 6-HR CONVECTIVE IMPROVEMENT. ANALYSIS INDICATES A
FAVORABLE ENVIRONMENT WITH WARM ALONG-TRACK SST, MEDIUM WESTWARD
AND POLEWARD OUTFLOW AND LIGHT TO MODERATE VWS. THE CYCLONE IS
TRACKING ALONG THE NORTHERN PERIPHERY OF THE STR TO THE SOUTH.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA.

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS SATCON: 54 KTS AT 170929Z
   CIMSS ADT: 55 KTS AT 170915Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TC EMNATI WILL CONTINUE WESTWARD UP TO TAU 12;
AFTERWARD, IT WILL TRACK MORE WEST-SOUTHWESTWARD TOWARD A WEAKNESS
IN THE STEERING STR WITH THE APPROACH OF A TRANSITORY MID-LATITUDE
TROUGH FROM THE SOUTHWEST. BY TAU 120, TC 13S WILL BE ALMOST MAKING
LANDFALL OVER CENTRAL MADAGASCAR JUST SOUTH OF TOAMASINA. THE
FAVORABLE ENVIRONMENT IS EXPECTED TO CARRY THROUGH THE MID-PORTION
OF THE FORECAST TRACK AND FUEL STEADY INTENSIFICATION TO A PEAK OF
95KTS BY TAU 72. AFTERWARD, LOW OCEAN HEAT CONTENT NEAR MADAGASCAR
CAUSED BY UPWELLING WITH THE PASSAGE OF ANOTHER TROPICAL CYCLONE A
FEW DAYS EARLIER, WILL CONTRIBUTE TO A GRADUAL WEAKENING - DOWN TO
75KTS BY TAU 120. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY GOOD AGREEMENT WITH
NAVGEM THE SOLE LEFT-OF-TRACK OUTLIER AFTER TAU 72, LENDING HIGH
CONFIDENCE IN THE JTWC TRACK FORECAST THAT IS LAID CLOSE TO THE
MODEL CONSENSUS (CONW) UP TO TAU 72 THEN JUST LEFT OF CONW
AFTERWARD TO OFFSET NAVGEM. 

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