WTPS12 NFFN 171200
TROPICAL DISTURBANCE ADVISORY NUMBER B18 ISSUED FROM RSMC NADI
Dec 171342 UTC.

SEVERE TROPICAL CYCLONE YASA CENTRE 920HPA WAS LOCATED NEAR 16.9S
179.8E AT 171200 UTC. POSITION POOR BASED ON HR HIMAWARI EIR IMAGERY
AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING EAST SOUTHEAST AT
ABOUT 10 KNOTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE
ESTIMATED AT ABOUT 120 KNOTS.

EXPECT WINDS OVER 63 KNOTS WITHIN 60 NAUTICAL MILES IN NE QUADRANT
AND WITHIN 60 NAUTICAL MILES IN SE QUADRANT
AND WITHIN 35 NAUTICAL MILES IN SW QUADRANT
AND WITHIN 50 NAUTICAL MILES IN NW QUADRANT

EXPECT WINDS OVER 47 KNOTS WITHIN 100 NAUTICAL MILES IN NE QUADRANT
AND WITHIN 100 NAUTICAL MILES IN SE QUADRANT
AND WITHIN 70 NAUTICAL MILES IN SW QUADRANT
AND WITHIN 90 NAUTICAL MILES IN NW QUADRANT

EXPECT WINDS OVER 33 KNOTS WITHIN 200 NAUTICAL MILES IN NE QUADRANT
AND WITHIN 180 NAUTICAL MILES IN SE QUADRANT
AND WITHIN 150 NAUTICAL MILES IN SW QUADRANT
AND WITHIN 150 NAUTICAL MILES IN NW QUADRANT

DEEP CONVECTION CONTINUES TO PERSIST WITH A CLOUD FILLED EYE.
ORGANISATION REMAINS GOOD. TC YASA LIES UNDER AN UPPER DIFFLUENT
REGION IN A MODERATE SHEARED ENVIRONMENT MOVING INTO A HIGH SHEARED
ENVIRONMENT WHICH MAY CAUSE WEAKENING. YASA IS BEING STEERED EAST-SOUTHEASTWARDS ALONG THE SOUTHERN PERIPHERY OF A NEAR EQUATORIAL
RIDGE TO THE NORTH. CYCLONIC CIRCULATION EXTENDS UPTO 500HPA. SST IS
AROUND 28 DEGREES CELSIUS. DVORAK ANALYSIS BASED ON EMBD PATTERN IN B
WITH 0.5 CF, 1.0 BANDING FEATURE YIELDING DT OF 6.0. MET 6.5 AND PT
6.0. FT BASED ON DT THUS, YIELDING T6.0/7.0/W1.0/24HRS


FORECASTS :
AT 12 HRS VALID AT 180000 UTC 18.2S 178.7W MOV SE AT 10 KT WITH 110
KT CLOSE TO CENTRE
AT 24 HRS VALID AT 181200 UTC 19.5S 177.7W MOV SE AT 09 KT WITH 110
KT CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 190000 UTC 20.7S 177.1W MOV SE AT 08 KT WITH 100
KT CLOSE TO CENTRE
AT 48 HRS VALID AT 191200 UTC 21.9S 177.6W MOV SSE AT 07 KT WITH 90
KT CLOSE TO CENTRE

THE NEXT TROPICAL DISTURBANCE ADVISORY ON YASA WILL BE ISSUED AROUND
152030 UTC.
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