WTIO30 FMEE 081228



RSMC / TROPICAL CYCLONE CENTER / LA REUNION

TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)



0.A WARNING NUMBER: 9/2/20172018

1.A TROPICAL CYCLONE  2  (IRVING)



2.A POSITION 2018/01/08 AT 1200 UTC:

WITHIN 20 NM RADIUS OF POINT 18.5 S / 77.9 E

(EIGHTEEN    DECIMAL FIVE   DEGREES SOUTH AND SEVENTY SEVEN

DECIMAL NINE   DEGREES EAST)

MOVEMENT : WEST-SOUTH-WEST 17 KT



3.A DVORAK ANALYSIS: 4.5/5.0/S 0.0/12 H



4.A CENTRAL PRESSURE: 966 HPA

5.A MAX AVERAGE WIND SPEED (10 MN): 75 KT

RADIUS OF MAXIMUM WINDS (RMW) :46 KM



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

28 KT NE: 190 SE: 480 SW: 300 NW: 150

34 KT NE: 140 SE: 300 SW: 240 NW: 120

48 KT NE: 90 SE: 170 SW: 110 NW: 90

64 KT NE: 60 SE: 60 SW: 60 NW: 60



7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1004 HPA / 700 KM

8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION : DEEP



1.B FORECASTS:

12H: 2018/01/09 00 UTC: 20.6 S / 75.2 E, MAX WIND=070 KT, TROPICAL

CYCLONE

24H: 2018/01/09 12 UTC: 22.6 S / 72.4 E, MAX WIND=065 KT, TROPICAL

CYCLONE

36H: 2018/01/10 00 UTC: 25.3 S / 69.6 E, MAX WIND=060 KT, SEVERE

TROPICAL STORM

48H: 2018/01/10 12 UTC: 29.3 S / 68.1 E, MAX WIND=050 KT, SEVERE

TROPICAL STORM

60H: 2018/01/11 00 UTC: 35.1 S / 70.5 E, MAX WIND=040 KT,

POST-TROPICAL DEPRESSION





2.B LONGER-RANGE OUTLOOK :







2.C ADDITIONAL INFORMATION:

T=4.5+ CI=5.0-



DURING THE LAST 6 HOURS, THE EFFECTS OF THE NORTHEASTERN CONSTRAINTE

ARE MORE AND MORE VISIBLE ON THE DEEP CONVECTION. LAST MW DATA (AMSR

AT 0652UTC AND SSMIS AT 1019UTC) SHOW A TILT BETWEEN LOW LEVEL AND

UPPER LEVEL, AND A WEAKNESS IN IRVING'S CORE STRUCTURE IS LOCATED IN

THE NORTHEASTERN SEMI-CERCLE.

THIS IS AN ANSWER AT THE GROWING MID-LEVEL SHEAR CONSTRAINT ALREADY

EXISTING OVER THE SYSTEM.



STILL NO CHANGE IN TERMS OF TRACK FORECAST FOR IRVING, ALL NUMERICAL

MODELS ARE IN EXCELLENT AGREEMENT ON ITS EVOLUTION, DEFINING THEN A

GOOD CONFIDENCE IN THIS FORECAST. IRVING'S TRACK IS STEERED BY A

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

ATTRACTED SOUTH-EASTWARDS TOWARD THE MID-LATITUDES BY A TROUGH

ARRIVING FROM THE SOUTH-WEST.



IRVING'S SPEED IS ALWAYS ALLOWING IT TO LIMIT THE EFFECTS OF AN UPPER

NORTH-EASTERLY SHEAR CONSTRAINT. THE VERTICAL WIND SHEAR SHOULD

INCREASE TODAY AND ALSO ON WEDNESDAY AHEAD OF THE UPPER ATMOSPHERIC

DYNAMICS, SO THE SYSTEM SHOULD BEGIN TO WEAKEN SLOWLY DUE TO THE

PERSISTING GOOD POLAR OUTFLOW, THE HIGH SPEED OF IRVING.

ON WEDNESDAY, THE OCEANIC POTENTIAL WILL STRONGLY DECREASE SOUTH OF

27S. IRVING SHOULD THEN BEGIN ITS EXTRATROPICAL TRANSITION BEFORE

MERGING WITH THE SYSTEM EX-AVA, THEN WITH A BAROCLINIC FRONTAL SYSTEM

CIRCULATING SOUTH OF 40S.=