The 2011–12 South-West Indian Ocean cyclone season was a slightly above average event in tropical cyclone formation. It began on November 15, 2011, and ended on April 30, 2012, with the exception for Mauritius and the Seychelles, for which it ended on May 15, 2012. These dates conventionally delimit the period of each year when most tropical cyclones form in the region; however, Severe Tropical Storm Kuena developed in early June, after the season had officially ended. The basin is defined as the area west of 90°E and south of the Equator in the Indian Ocean, which includes the waters around Madagascar westward to the east coast of Africa. Tropical cyclones in this basin are monitored by the Regional Specialised Meteorological Centre in Réunion.
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Timeline
Systems
Moderate Tropical Storm Alenga
On December 5, a rapidly developing area of low pressure crossed 90°E and entered La Réunion's area of responsibility. Within hours of moving into the region, the Joint Typhoon Warning Center (JTWC) classified it as Tropical Cyclone 01S. By this time, a banding eye feature was apparent on satellite imagery. Favorable atmospheric conditions allowed convection to increase in intensity and coverage over its center and good outflow. Several hours later, La Réunion reported that the system had intensified into a Moderate Tropical Storm, with the Mauritius Meteorological service naming it Alenga. The name was contributed by Kenya. Continuing to rapidly intensify, Alenga strengthened into a severe tropical storm later that day. Although predicted to intensify into a tropical cyclone, Alenga weakened near midday December 6, and was downgraded to moderate tropical storm status before it moved out of the South-West Indian Ocean (SWIO) and into the Australian region, early on December 7.
Tropical Depression 02
On December 6, Météo-France declared a tropical disturbance a tropical depression. On December 7, the cyclone entered an area of strong vertical wind shear causing the low level circulation centre to become exposed. Soon afterwards, Tropical Depression 02 dissipated to a remnant low. However, early on December 8, the system regenerated into a weak tropical depression. Later on December 8, convection redeveloped, and wrapped around the low level center, even as the storm continued moving westward, as it slowly weakened. Late on December 9, Météo-France issued their last advisory on the storm as it weakened below tropical depression intensity.
Subtropical Depression 03
An area of low pressure located near the southeastern coast of Madagascar, that was previously being tracked by the JTWC as Invest 93S, was designated a subtropical depression by Météo-France, on December 19. The system did not move much, and persisted through the 20th. However, on December 21, the subtropical depression began to weaken as it moved southward very slowly. Late on December 23, Météo-France issued their last advisory on the storm as it dissipated.
Heavy rainfall related to the depression killed 43 people in Madagascar.
Tropical Cyclone Benilde
On December 28, RSMC La Réunion reported that Tropical Disturbance 04 had moved into the region from the Australian region, where it had been monitored for about a week. During that day the disturbance gradually developed further which prompted the JTWC to start issuing advisories on the system and designate it as Tropical Cyclone 04S. On December 29, La Réunion upgraded the system to a moderate tropical storm, which was then named Benilde by Mauritius, a name contributed by Mozambique. Benilde moved in a general westward direction and quickly intensified into a tropical cyclone by December 31. The storm then took turned onto a more southwesterly path as it continued to strengthen. This period of continued strengthening did not last long. On January 1, dry air began to make its way into the southern area of the storm. Convection increased for a short period of time, but later in the day La Réunion noted that Benilde's northern eyewall had collapsed and the system was weakening after reporting 10-minute sustained peak wind speeds of . On January 3, Benilde weakened into a Severe Tropical Storm. Suffering from severe wind shear, the system continued weakening and it became a tropical depression on January 4, while completely absorbing a weak disturbance to the north, late during that day. Early on January 5, Benilde weakened some more, as its northern structure collapsed completely, and the convection was displaced, to the south of the storm's center as it degenerated into an extratropical cyclone.
Moderate Tropical Storm Chanda
On January 4, Météo-France noted an area of strong convective activity in the Mozambique Channel embedded within the Intertropical Convergence Zone and identified the genesis of a low level circulation near the coastline of Mozambique. The zone of disturbed weather persisted over the next several days and on the morning of January 8, Météo-France declared that a tropical disturbance had formed. Six hours later, the system was upgraded to a Tropical Depression as it drifted southeastwards towards Morondava, Madagascar, and after a further six hours it was named Moderate Tropical Storm Chanda, a name contributed by Mauritius. But after making landfall on Madagascar, late on January 8, Chanda began to weaken, as it moved further inland, towards Southern Madagascar. Early on January 10, Chanda emerged off the coast of southeastern Madagascar, and into the Indian Ocean. Chanda then slightly restrengthened, but soon began to weaken, as it encountered more wind shear. Early on January 11, Chanda's northern structure began to collapse, as it continued to move east-southeast slowly. Chanda soon transitioned into an extratropical cyclone, which prompted the last advisory on the storm to be issued.
Across Madagascar, Chanda produced heavy rains. In a 48‑hour period, of rain fell. Significant flooding in the country isolated several communities and inundated numerous homes. At least one person drowned in Miandrivazo.
Subtropical Depression Dando
An extratropical disturbance formed east of Madagascar on January 11, and transitioned into a subtropical depression the next day. It retained subtropical characteristics as it moved towards the African mainland, but by January 15, it reached the equivalent of cyclone strength and was allocated the name Dando by NWS Madagascar. The name was provided by Tanzania. On January 16, the last advisory was issued for Dando, as the system weakened to a remnant low. After making landfall on January 17, the remnants of Dando moved inland, before dissipating on January 18.
Dando was the first storm since Tropical Storm Domoina in 1984 to hit southern Mozambique. Heavy rains across southern parts of the country triggered significant flooding, prompting officials to urge residents in flood-prone areas to evacuate. Along the coast, waves up to prevented fishermen from leaving port. Rains from the storm also impacted parts of Zimbabwe and Swaziland. In Kruger National Park in South Africa hundreds of tourists and locals were left stranded and at least 30 people had to be airlifted after flash floods washed away bridges and damaged numerous buildings and roads in the area. The final death toll from the storm stood at 10, including six in South Africa's Mpumalanga province after heavy rains fueled by its remnants burst the banks of the Olifants River.
Severe Tropical Storm Ethel
On January 18, RSMC La Réunion started to monitor a tropical disturbance that had developed to the northeast of Rodrigues. During that day the disturbance gradually developed further before during the next day it was named as Ethel by the Mauritius Meteorological Service as it reached tropical storm strength. Late on January 19, Ethel intensified into a severe tropical storm, and continued to intensify into a category 1 equivalent tropical cyclone, on January 20,. Cool sea surface temperatures and not very favorable wind shear made Ethel unable to intensify further, with the system weakening back to a Moderate Tropical Storm on January 22,. Soon, convection was displaced, to the south of the storm's center, as it degenerated into an extratropical cyclone, on January 23,. As a result, the JTWC issued their last warning on the system.
Passing near Rodrigues, the storm produced high winds and heavy rains across the island. In a 24‑hour span, of rain fell on the island. Significant damage was reported on the island and communication was disrupted. Injuries were also reported in the wake of the storm. One person died from electrocution in an event related to the cyclone.
Intense Tropical Cyclone Funso
On January 17, RSMC La Réunion started to monitor an area of low pressure that had developed within the Mozambique Channel about 620 km (365 mi) to the northwest of Antananarivo, Madagascar. Over the next two days the area of low pressure rapidly developed further in an area of favourable conditions.
During the overnight hours of January 18, a ship carrying 54 people sank on its way from Anjouan to Mayotte amidst rough seas produced by Funso. At least 15 passengers drowned while dozens remain missing. The Mpumalanga and Limpopo regions of South Africa, which were hit by flooding from Dando, was at risk of further flooding and waterborne diseases by January 20.
Early on January 19, RSMC La Réunion declared the disturbance Tropical Depression 08, shortly before the JTWC also initiated advisories and declared the depression "Tropical Cyclone 08S" as it became equivalent to a tropical storm. Later that day the Malagasy national weather service named the storm Funso before early the next day as it continued to intensify quickly, RSMC La Réunion declared that Funso had intensified into a tropical cyclone. Due to land interaction, Funso weakened slightly on January 22–23, but soon reintensified into an intense tropical cyclone as it started heading south. Although the core of the storm remained offshore, over three million people were affected by tropical storm-force winds. Funso strengthened a little more on January 24, as it continued to move southward slowly. However, early on January 25, Funso began to weaken, due to an eyewall replacement cycle. remarked that Funso weakened below intense tropical cyclone intensity early on January 25. At the same time, the JTWC estimated the cyclone intensified further to peak 1 minute sustained winds of , based on estimates via the Dvorak technique. The agency noted that the eyewall replacement cycle finished and produced a well-defined eye 28 km (17 mi) in diameter. At 1200 UTC on January 25, MF again upgraded Funso to an intense tropical cyclone, and later that day, the cyclone began another eyewall replacement cycle, and started to develop a larger eye, measuring 55 km across. On January 27, Funson underwent yet another eyewall replacement cycle on January 27, as it started weakening. On the next day, Funso became extratropical, due to strong wind shear and colder waters. For the next few days, Funso's remnants moved eastward, before dissipating on February 1.
On January 23, national television in Mozambique announced 12 deaths in the northern Zambezia Province, following the intense cyclone's passage close to land. Seven of the fatalities occurred in the Maganja da Costa District and one was in the provincial capital Quelimane. More than 5000 people were displaced by the weather conditions and the only road connecting the capital Maputo to the north was reported to be seriously damaged when the Komati River flooded its banks, cutting off the capital city. At least 70,000 people were without a clean drinking water supply following the storm, and more than 56,000 were left homeless in Mozambique.