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2017-18 South-West Indian Ocean cyclone season

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2017-18 South-West Indian Ocean cyclone season
First storm formed October 5, 2017
Last storm dissipated Season currently active
Strongest storm Cherono — 165 mph, 889 mbar
Total disturbances 13
Tropical depressions 12
Total storms 9
Tropical cyclones 5
Intense cyclones 3
Total damages $4.2 billion (2018 USD)
Total fatalities 770

The 2017-18 South-West Indian Ocean cyclone season was a hyperactive season, with 31 named storms and 23 tropical cyclones. It began on November 1, 2017 and ended on April 30, 2018, dates which conventionally delimit the year in which most tropical cyclones form in the basin. However any tropical cyclone that developed between July 1, 2017, and June 30, 2018 would have count towards the seasonal count. The South-West Indian Ocean basin is defined as being to the south of the equator and between the coast of Africa and 90°E. The basin is monitored by Meteo France in Réunion (MFR), while the Madagascan Weather Service (MWS) and Mauritius Meteorological Service (MMS) name tropical cyclones when they reach moderate tropical storm intensity. The Joint Typhoon Warning Center (JTWC) also issue warnings for the basin, designating tropical cyclones with a number and an "S" suffix.

Season summary

wikipedia:Tropical cyclone scales#Comparisons across basins

Storms

Tropical Disturbance 01

Tropical disturbance (MFR)
01R 2017.jpg
Duration October 5 – October 14
Peak intensity 30 mph (45 km/h) (1-min)  999 mbar (hPa)

A zone of disturbed weather (ZDW) was first mentioned in La Reunion's Tropical Weather Outlook (TWO) on October 3. They said that it would slowly strengthen into a tropical disturbance and then later a tropical depression. The ZDW then strengthened into a tropical disturbance on October 5, less than a month before the official start to the South-West Indian Ocean (SWIO) cyclone season. However, due to strengthening wind shear, the system was no longer forecast to become a tropical depression. The disturbance was stationary until October 14, when a system in the North Indian Ocean absorbed 01.

Tropical Depression 02

Tropical depression (MFR)
02R 2017.jpg
Duration October 31 (moved into basin) – November 3
Peak intensity 35 mph (55 km/h) (1-min)  1002 mbar (hPa)

A tropical low formed north of Exmouth, Australia on October 24 where tropical cyclone watches had been issued. Those were immediately cancelled when the low was then forecast to move into the SWIO basin. Once the system had crossed 90°E, the system was numbered 02 by the MFR and was classified as a tropical depression on October 31. The next day, the depression had turned to the south and started to encounter cooler sea surface temperatures (SST). However, the system maintained intensity until November 3 when it became an extratropical cyclone.

Intense Tropical Cyclone Abele

Intense tropical cyclone (MFR)
03R 2017.jpg
Duration November 12 – November 19
Peak intensity 105 mph (165 km/h) (1-min)  959 mbar (hPa)

A ZDW formed east of Madagascar on November 12 and rapidly strengthened into a tropical depression and was numbered '03'. Hours later, the JTWC had issued a Tropical Cyclone Formation Alert (TCFA) on the system. During the morning hours of November 13, Tropical Depression 06 had strengthened into Moderate Tropical Storm Abele and the JTWC began issuing warnings on 02S. The storm rapidly strengthened on November 15, when Abele became a tropical cyclone. Additional strengthening occurred during the night of November 15–16, when the cyclone became an intense tropical cyclone, with 10-min sustained winds of 105 mph. It began weakening due to cooler SSTs and higher wind shear. By November 18, the storm was just located south-west of Madagascar as a minimal moderate tropical storm. This prompted the JTWC to issue its final warning on Abele. It rapidly weakened to a tropical disturbance on November 19 and dissipated. No watches or warnings were issued due to Abele.

Severe Tropical Storm Bingiza

Severe tropical storm (MFR)
04R 2017.jpg
Duration November 25 – November 29
Peak intensity 70 mph (110 km/h) (1-min)  981 mbar (hPa)

The MFR had noted a small low pressure area located in the Mozambique Channel on November 24, which became a tropical depression the next day. A Cyclone Warning was issued for Mozambique at 0600 UTC on November 26 as the depression strengthened into Moderate Tropical Storm Bingiza. As the storm neared the Mozambique coast, 15,000 people were evacuated from the coastline. Soon after, Bingiza strengthened into a severe tropical storm with winds of 70 mph. At 0745 UTC on November 28, Bingiza made landfall near Beira, causing widespread flooding. The system rapidly weakened into a ZDW and dissipated on November 29.

Bingiza caused $3.2 billion in damage and killed 129 people. Due to this, Bingiza was retired during the summer of 2018.

Very Intense Tropical Cyclone Cherono

Very intense tropical cyclone (MFR)
Counterclockwise vortex
Duration December 8 – December 24
Peak intensity 165 mph (270 km/h) (1-min)  889 mbar (hPa)

A low pressure system formed about 1,015 miles east of La Reunion on December 8, and gained a circulation hours later. At 1200 UTC on December 28, RSMC La Reunion classified this system as a Moderate Tropical Storm, and Mauritius named the storm Cherono. The system rapidly strengthened to tropical cyclone strength in 12 hours, and strengthened again to an intense tropical cyclone six hours later. In the afternoon hours of December 9, the JTWC had issued a TCFA on the system, while only hours later designating the system as '03S'. At the same time, RSMC La Reunion had upgraded Cherono to a Very Intense Tropical Cyclone, with winds of 150 mph and a central pressure of 901 mb. It strengthened even further on December 12, when it had become the strongest South-West Indian Ocean cyclone ever recorded with a central pressure of 889 mb.

Tropical Depression 06

Tropical depression (MFR)
Counterclockwise vortex
Duration December 11 – December 12
Peak intensity 35 mph (55 km/h) (1-min)  1006 mbar (hPa)

A tropical depression formed on December 11 south of La Reunion with 10-min sustained winds of 35 mph. However, early on December 12, the depression was absorbed by much larger Cyclone Cherono.

Tropical Cyclone Dalilou

Tropical cyclone (MFR)
Counterclockwise vortex
Duration December 16 (moved into basin) – December 19
Peak intensity 75 mph (120 km/h) (1-min)  988 mbar (hPa)

A tropical low formed in the Australian region on December 3, and then on December 11, made landfall near Darwin. The storm caused 13 deaths and $6.4 billion in damage in Australia. The storm then moved across Western Australia and into the SWIO on December 16. It already had sustained winds of 35 mph, and was classed as a tropical depression. It slowly strengthened into a moderate tropical storm on December 17, with Mauritius naming it Dalilou. It strengthened more in twelve hours, and became a severe tropical storm. On December 18, Dalilou strengthened into a tropical cyclone with winds of 75 mph. The next day, Dalilou became extratropical, however, it still had winds equivalent to a tropical cyclone. The extratropical remnants of the storm moved southwards rapidly until dissipating north of Vostok, Antarctica on December 24.

Moderate Tropical Storm Elvire

Moderate tropical storm (MFR)
Counterclockwise vortex
Duration December 20 – December 22
Peak intensity 45 mph (75 km/h) (1-min)  997 mbar (hPa)

A tropical disturbance formed on December 20 just off the coast of Mauritius and strengthened into a tropical depression. Over 23 inches of rain was recorded in Bel Air, Mauritius, while 20 inches was recorded in Goodlands. Three people died due to the floods, according to officials. By December 21, the depression had strengthened into Moderate Tropical Storm Elvire. Shortly after, the storm made landfall on Mauritius and weakened significantly and dissipated the next day.

Severe Tropical Storm Francis

Main article: Tropical Storm Francis
Severe tropical storm (MFR)
Counterclockwise vortex
Duration December 28 – January 3
Peak intensity 65 mph (100 km/h) (1-min)  969 mbar (hPa)

On December 28, RSMC La Reunion reported that a tropical disturbance had developed about 71 miles north-west of Anorotsangana. Six hours later, it had strengthened into a depression, and later a moderate tropical storm and was named Francis. The RSMC began issuing Cyclone Warnings for the northwestern Madagascar coast and cyclone watches for the west coast. The storm maintained its strength until January 3, when it strengthened into a Severe Tropical Storm. It made landfall near Antananabe, Madagascar at 1923 UTC. It weakened rapidly and dissipated by the next advisory at 0000 UTC on January 4.

Tropical Depression 10

Tropical depression (MFR)
Counterclockwise vortex
Duration December 30 – January 2
Peak intensity 35 mph (55 km/h) (1-min)  994 mbar (hPa)

The RSMC La Reunion reported that a tropical depression had formed about 620 miles northeast of Mauritius on December 30. However, an area of thunderstorms that had developed earlier in the day had absorbed the depression on January 2.

Five people that were aboard a ship died due to the ship sinking.

Very Intense Tropical Cyclone Haingo

Main article: Cyclone Haingo
Very intense tropical cyclone (MFR)
Haingo 2018 track.png
Duration January 4 – January 8
Peak intensity 145 mph (230 km/h) (1-min)  903 mbar (hPa)

A Moderate Tropical Storm formed on January 4, and six hours later, strengthened into a Very Intense Tropical Cyclone with winds of 145 mph, making it the fastest intensifying SWIO storm ever recorded. It maintained its peak strength until January 5, when it weakened to a Category 2 due to an eyewall replacement cycle. However, this did not last long as Haingo restrengthened back to a Category 4. Due to increasing wind shear, the cyclone began to weaken during that evening and was down to a Tropical Cyclone by January 5. Slight restrengthening occurred later that day, where Haingo reached a third peak of 115 mph winds. The system then weakened as it picked up forward speed, and dissipated on January 8 as a Moderate Tropical Storm.

Tropical Cyclone Igor

Tropical cyclone (MFR)
Counterclockwise vortex
Duration January 12 – January 21
Peak intensity 85 mph (140 km/h) (1-min)  949 mbar (hPa)

A deep low pressure system had formed north-east of Mauritius, and developed into a moderate tropical storm six hours later, assigning the name Igor. The storm strengthened further on January 15, when it became a severe tropical storm with sustained winds of 70 mph. The next day, Igor became a tropical cyclone and made landfall on Mauritius, bringing power outages that lasted for over a week. It maintained its intensity until January 19, when it began to weaken due to increasing wind shear. Igor eventually dissipated on January 21.

Moderate Tropical Storm Jani

Moderate tropical storm (MFR)
Jani 2018 track.png
Duration January 22 – January 25
Peak intensity 50 mph (85 km/h) (1-min)  992 mbar (hPa)

RSMC La Reunion noted that an area of convection had persisted in the northern Mozambique Channel. A few hours later, the center upgraded the area of convection to Tropical Depression 13. However, the system was shortly downgraded to a tropical disturbance as wind shear increased.

The system regained its convection and reattained its circulation, and was upgraded to a Moderate Tropical Storm, with NWS Madagascar naming it Jani.

Season effects

This table lists all the storms that developed in the Southern Hemisphere during the 2017–2018 South-West Indian Ocean cyclone season. It includes their intensity, duration, name, landfalls, deaths, and damages. All data is taken from Météo-France. The damage figures are all from 2018 USD.

Storm
Name
Dates active Storm category
at peak intensity
Peak 10-min
sustained winds
Pressure
hPa
Areas affected Damage
(USD)
Deaths
01 N/A October 5 –14 Tropical Disturbance 45 km/h (30 mph) 999 None None None
02 N/A October 31 – November 3 Tropical Depression 55 km/h (35 mph) 1002 None None None
03/02S Abele November 12 – 19 Intense Tropical Cyclone 165 km/h (105 mph) 959 Madagascar None None
04 Bingiza November 25 – 29 Severe Tropical Storm 110 km/h (70 mph) 981 Madagascar, Mozambique $3.2 billion 129
05/03S Cherono December 8 – 24 Very Intense Tropical Cyclone 265 km/h (165 mph) 889 None None None
06 N/A December 11 – 12 Tropical Depression 55 km/h (35 mph) 1006 Reunion None 1
07/06S Dalilou December 16 – 19 Tropical Cyclone 120 km/h (75 mph) 988 None None None
08 Elvire December 20 – 22 Moderate Tropical Storm 75 km/h (45 mph) 997 Mauritius, Reunion $600 million 3
09/11S Francis December 28 – January 3 Severe Tropical Storm 100 km/h (65 mph) 969 Madagascar $300 million 631
10 N/A December 30 – January 2 Tropical Depression 55 km/h (35 mph) 994 None None 5
11/14S Haingo January 4 – January 8 Very Intense Tropical Cyclone 230 km/h (145 mph) 903 Reunion None None
12/17S Igor January 12 – 21 Tropical Cyclone 140 km/h (85 mph) 949 Reunion $100 million 1
13/19S Jani January 22 – 25 Moderate Tropical Storm 85 km/h (50 mph) 992 Mozambique, Madagascar None None
Season Aggregates
12 systems October 5 – active 265 km/h (165 mph) 889 $4.2 billion 770

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