2023–24 South-West Indian Ocean cyclone season

The 2023–24 South-West Indian Ocean cyclone season was an above-average season, including ten named storms (including an unnamed tropical storm), six tropical cyclones and two intense tropical cyclones. Despite its moderate activity, it was the least deadly season in four years, causing only 53 deaths, most of which were caused by cyclones Alvaro and Gamane. It began on 15 November 2023, and ended on 30 April 2024, with the exception for Mauritius and the Seychelles, where it ended on 15 May 2024. These dates conventionally delimit the period of each year when most tropical and subtropical cyclones form in the basin, which is west of 90°E and south of the Equator. However, tropical cyclones can form year-round, and all tropical cyclones that formed between 1 July 2023 and 30 June 2024 would be part of the season. Tropical and subtropical cyclones in this basin are monitored by the Regional Specialised Meteorological Centre in Réunion and unofficially by the Joint Typhoon Warning Center. __TOC__

Seasonal forecasts Records Moderate TropicalStorms Very/IntenseTropical CyclonesRecord high: 15 9 Record low: 3 0 Forecast CenterSystemsMauritius Meteorological Services6–8 tropical cyclonesMétéo-France5–8 tropical cyclonesForecast CenterChance of above averageMétéo-France10%20%70%Source: Seasonal Outlook for Tropical Cyclones. In October 2023, Météo-France issued its seasonal forecast of cyclone activity for the basin, predicting a below-average season with 5–8 moderate tropical storms due to an expected strong El Niño event. The MFR also stated that the chance for a below-average season was 70%. Average cyclone activity was given a 20% chance, while an above-average level of activity was given a 10% chance.

The Mauritius Meteorological Services (MMS) also released their summer outlooks for the season, stating that around six to eight cyclones were expected to form, with the region west of Diego Garcia having environmental conditions more conducive for cyclogenesis.

Seasonal summary

The ACE index for the 2023–24 South-West Indian Ocean cyclone season as calculated by Colorado State University was 106.7 units. Through 2024, five tropical cyclones, four of which became tropical storms, formed outside the cyclone season in the southwest Indian Ocean, tying 2003 with four named storms. Season starts The season officially started on 15 November 2023, however the first system, Alvaro, would not form until 30 December. Alvaro became a tropical depression the next day, traversing the Mozambique Channel, before making landfall in Morombe District, Madagascar on 1 January 2024. After a brief lull in activity, Tropical Cyclone Belal formed on 11 January. Belal would affect Mauritius and Reunion, killing six people. On 22 January, Moderate Tropical Storm Candice formed. On 25 January, Intense Tropical Cyclone Anggrek entered the basin, while Tropical Depression 05 emerging northeast of St. Brandon. After a lull period of about 3 weeks, the strongest storm being Intense Tropical Cyclone Djoungou from 13 February and exited the basin 6 days later. 17 February was the day Severe Tropical Storm Eleanor brought intense rainfall and winds which left at least 2 people injured, 10,000 customers deprived of electricity, several electricity pylons damaged, and toppled trees blocking several roads. It is the northern regions which suffered the greatest damage. Severe Tropical Storm Filipo emerged on 2 March near Mozambique affecting 48,000 people and damaging 8,000 houses. Tropical Depression Neville crossed into the basin on 24 March but MFR discontinued warning issuance. Short-lived Tropical Cyclone Gamane emerged on 25 March north-northeast of Toamasina, Madagascar, causing a total of 19 deaths, 3 people missing and at least 90,000 affected.

Off-season The season ended with 1 tropical cyclone each in April and May. At the very end of April, Tropical Cyclone Hidaya formed near Seychelles and was the third tropical cyclone or depression in recorded history to make landfall in Tanzania, the others being an unnamed cyclone in 1952 and Tropical Depression Atang in 2002. Then on 16 May Tropical Cyclone Ialy formed east-northeast of Comoros, killing 2 people; strong winds tore off the roof of a school, killing a girl and injuring four others, while another person died due to a fallen wall.

Systems Tropical Cyclone Alvaro

In December 2023, the MFR began to monitor the potential for tropical cyclogenesis as Kelvin waves and Rossby waves intersected in the western portion of the agency's area of responsibility, ahead of a wet phase of the Madden–Julian oscillation (MJO). By 29 December, a monsoon trough had produced convection southeast of Beira, Mozambique that spun, as convergence of winds increased within the system's closed surface circulation. The next day, the MFR classified the system as a tropical disturbance. Tracking southeast under the influence of a ridge, the disturbance was further upgraded to a tropical depression by the MFR on 31 December. The warm core consolidated, causing the system to intensify into a moderate tropical storm and receive the name Alvaro, with JTWC designated as Tropical Cyclone 04S.

During 1 January 2024, Alvaro's maintenance of a curved band and the emergence of an eye prompted the MFR to upgrade the system to a severe tropical storm, as Alvaro continued to strengthen under favorable conditions despite vertical wind shear in the mid-level troposphere. Alvaro later made landfall in Morombe District, Madagascar, bringing sustained winds of and gusts of . Alvaro rapidly weakened due to the mountainous terrain of the island nation, with rainbands around the core no longer present. Alvaro re-entered the Indian Ocean on 3 January, re-intensifying back into a moderate tropical storm. By 18:00 UTC, the MFR classified Alvaro as a post-tropical depression after the storm had lost its tropical characteristics. The MFR issued its final bulletin on Alvaro on 4 January, as the system interacted with the baroclinic zone. Total damages are estimated to be greater than US$1 million.

Tropical Cyclone Belal

On 11 January, the MFR marked a zone of disturbed weather, citing the conducive conditions induced by the MJO and an equatorial Rossby wave. The monsoon trough north-northeast of Madagascar had intensified several days prior, as convergence transferred moisture aloft. Concentration of convection near the center increased, particularly in the western section, as the system moved south. By the next day, the JTWC issued a Tropical Cyclone Formation Alert (TCFA) on the potential disturbance, since it was in an environment of very warm sea surface temperatures, high ocean heat content, low vertical shear, and excellent outflow. At 12:00 UTC, the MFR categorized the system as a tropical depression. Additionally, microwave imagery indicated an eye in the lower-layer while the storm steered more westward, and the JTWC began issuing advisories on the system as a tropical cyclone. By 13 January, it intensified to a moderate tropical storm, prompting the MMS to name it Belal. Intense lightning activity within the center further signaled a period of rapid intensification, leading to Belal becoming a severe tropical storm. As the storm developed a well-defined eye, the MFR upgraded Belal to a tropical cyclone early on 14 January. However, while Belal recurved southeastward, wind shear began to deteriorate the storm's structure into becoming asymmetrical. The eyewall then struck the island of Réunion during the next day. The storm briefly weakened back into a severe tropical storm, before again becoming a tropical cyclone on 16 January after organization of the CDO. Weakening then continued from dry air intrusion, causing Belal to become a moderate tropical storm on the next day. By the end of 18 January, Belal had degenerated into a remnant low.

As the system developed, the MFR issued a yellow cyclone pre-alert for Réunion on 13 January, which was upgraded to an orange cyclone alert on 15:00 UTC the next day. On 13 January, the MMS raised a class I cyclone warning for Mauritius. On 14 January, the MFR upgraded the orange alert into a red alert for Réunion as Belal neared the island. The next day, the MFR hoisted a purple alert for Réunion as Belal neared the coast. The eyewall of Belal remained just offshore the northern coast of Réunion during the storm's closest passage. Four people died during the storm in Réunion. Around 150,000 electricity customers lost power, representing more than a third of the island's population. Around 37,000 people lost access to water. Two people died in Mauritius.. After the storm's passage, Mauritius' head of meteorology stepped down after his institution was accused of "not giving adequate warning about the storm’s impact."

Severe Tropical Storm Candice

On 17 January, the MFR noted in its daily bulletin that a strong surge of monsoon flow northeast of the Mascarenes could produce a precursor vortex. By 22 January, the MFR began releasing warnings on a broad but ill-defined circulation. Convection was offsetted far from the center as the system turns from south to southwest under the influence of a low-level ridge. Upper-level divergence in conjunction with warm sea surface temperatures subdued the effects of vertical shear, enabling consolidation of the disturbance. On 23 January, the JTWC issued a TCFA for the system. The next day, the MFR reported that the system intensified into a tropical depression at 06:00 UTC on 24 January, before the MMS upgraded the system to a moderate tropical storm two hours later, naming it Candice. On 25 January, the JTWC followed suit in recognising the system as Tropical Cyclone 08S. Candice eventually encountered more hostile environmental conditions, as wind shear began to increase dramatically. Convective activity associated with Candice became limited to the cyclone, the MFR estimated that the system had peaked as a severe tropical storm with 10-minute sustained winds of . Environmental conditions and increasingly strong wind shear displaced the storm's convection, weakening it further. Candice degenerated into a post-tropical depression on 27 January as deep convective had ceased, and the final advisory was then issued by MFR. The same day, the JTWC issued its final warning on the system as it became a weakly defined system with an exposed low-level circulation center (LLCC).

Intense Tropical Cyclone Anggrek

On 25 January, Severe Tropical Cyclone Anggrek moved into the basin from the Australian region and was classified as a tropical cyclone. Anggrek strengthened into a Category 3 equivalent cyclone around 09:00 UTC on 26 January, after eye had emerged on satellite imagery, surrounded by a ring of cloud tops. Six hours later, the cyclone maintained a well-defined eye, and the MFR later upgraded the system to an intense tropical cyclone. The cyclone was highly compact, with a distinct eye. The cyclone weakened and bottomed out at on 28 January. Later the next day, the JTWC stated that Anggrek peaked with one-minute sustained winds of —equivalent to a Category 4 hurricane. Around the same time, the convection decreasingly organized and wrapped around the LLCC. The system was moving quickly southeastwards, steered by a ridge to its east. Shortly afterward, Anggrek's cloud pattern slightly deteriorated; it then weakened due to strong wind shear. Soon after, Anggrek's eye gradually disappeared from infrared and visible satellite imagery. The MFR issued its last advisory on the storm as the convective structure weakened further at 18:00 UTC on 30 January. Later the next day, the JTWC discontinued warnings.

Tropical Depression 05