WTIO30 FMEE 070815



RSMC / TROPICAL CYCLONE CENTER / LA REUNION

TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)



0.A WARNING NUMBER: 4/2/20172018

1.A SEVERE TROPICAL STORM  2  (IRVING)



2.A POSITION 2018/01/07 AT 0600 UTC:

WITHIN 30 NM RADIUS OF POINT 13.9 S / 85.7 E

(THIRTEEN    DECIMAL NINE   DEGREES SOUTH AND EIGHTY FIVE    DECIMAL

SEVEN   DEGREES EAST)

MOVEMENT : WEST-SOUTH-WEST 14 KT



3.A DVORAK ANALYSIS: 3.5/3.5/D 0.5/12 H



4.A CENTRAL PRESSURE: 985 HPA

5.A MAX AVERAGE WIND SPEED (10 MN): 50 KT

RADIUS OF MAXIMUM WINDS (RMW) :46 KM



6.A EXTENSION OF WIND BY QUADRANTS (KM):

28 KT NE: 220 SE: 330 SW: 330 NW: 220

34 KT NE: 150 SE: 190 SW: 190 NW: 110

48 KT NE: 90 SE: 110 SW: 110 NW:





7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1006 HPA / 800 KM

8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION : DEEP



1.B FORECASTS:

12H: 2018/01/07 18 UTC: 15.5 S / 82.6 E, MAX WIND=055 KT, SEVERE

TROPICAL STORM

24H: 2018/01/08 06 UTC: 17.6 S / 79.7 E, MAX WIND=065 KT, TROPICAL

CYCLONE

36H: 2018/01/08 18 UTC: 20.3 S / 76.9 E, MAX WIND=070 KT, TROPICAL

CYCLONE

48H: 2018/01/09 06 UTC: 22.6 S / 73.7 E, MAX WIND=060 KT, TROPICAL

CYCLONE

60H: 2018/01/09 18 UTC: 25.3 S / 70.9 E, MAX WIND=050 KT, SEVERE

TROPICAL STORM

72H: 2018/01/10 06 UTC: 29.4 S / 69.1 E, MAX WIND=040 KT, MODERATE

TROPICAL STORM



2.B LONGER-RANGE OUTLOOK :

96H: 2018/01/11 06 UTC: 39.1 S / 73.0 E, MAX WIND=040 KT,

POST-TROPICAL DEPRESSION





2.C ADDITIONAL INFORMATION:

T=CI=3.5+



DURING THE LAST HOURS, CLOUDS TOPS GOT WARMER WHILE A BROAD EYE

APPEARED ON INFRARED IMAGERY. MICROWAVE DATA CONFIRMED THE

STRENGTHENING OF THE INNER CORE. DVORAK ESTIMATES ARE AROUND 3.5 AND

4.0 BUT LAST ASCAT SWATHS DO NOT EXCEED 45KT. ITS LARGE STRUCTURE MAY

EXPLAIN THAT DIFFERENCE. IRVING IS SO UPGRADED TO SEVERE TROPICAL

STORM STATUS WITH 50KT FOR MAXIMUM WINDS .



NO CHANGE IN TERMS OF FORECAST ON THE IRVING SYSTEM, ALL NUMERICAL

MODELS ARE WELL IN AGREEMENT ON ITS EVOLUTION, DEFINING THEN A GOOD

CONFIDENCE IN THE FORECAST. IRVING'S TRACK IS STEERED BY A STRONG

RIDGE IN THE SOUTH-EAST. FROM WEDNESDAY, IRVING SHOULD BE ATTRACTED

TOWARDS THE MID-LATITUDES BY A TROUGH ARRIVING FROM THE SOUTH-WEST.



THE SYSTEM IS LIKELY TO KEEP CONDUCIVE ENVIRONMENTAL CONDITIONS UP TO

TOMORROW EVENING WITH A VERY GOOD UPPER DIVERGENCE. IT SHOULD REACH

TROPICAL CYCLONE STATUS IN THE NEXT MORNING. THEN, AHEAD OF THE UPPER

ATMOSPHERIC DYNAMICS DESPITE ITS SIGNIFICANT SPEED, SHEAR NEGATIVE

IMPACTS ARE LIKELY TO LIMIT ITS DEEPENING POTENTIAL AND THEN WEAKEN

IRVING FROM TUESDAY. ON THURSDAY, THE OCEANIC POTENTIAL AS WELL WILL

DECAY SOUTH OF 27S. IRVING SHOULD THEN BEGIN ITS EXTRATROPICAL

TRANSITION.=