The 2010–11 South-West Indian Ocean cyclone season was the least active cyclone season on record in the basin, tied with 1982–83, producing only three systems of gale intensity. This was due to cooler than normal water temperatures and the Walker circulation – a broad atmospheric circulation – causing unusually moist conditions in the eastern Indian Ocean and unusually dry conditions in the western Indian Ocean. The basin includes the waters of the ocean south of the equator and west of 90º E to the eastern coast of Africa.
There were nine tropical or subtropical cyclones during the season, including five weak tropical disturbances or depressions, mostly in the northeastern portion of the basin or to the east of Madagascar. The first of these systems developed on 25 October 2010, which had its origins in the northeastern portion of the basin. On 29 November, the first named storm – Abele – also formed in the same area, strengthening to become one of the season's two tropical cyclones – storms with maximum sustained winds of at least . The strongest system of the season was Cyclone Bingiza, which attained peak winds of off the northeastern coast of Madagascar in February. Bingiza was also the only storm to cause severe effects on land, causing heavy damage and 34 fatalities across Madagascar. Moderate Tropical Storm Cherono developed in March and traversed much of the ocean, only brushing by the island of Rodrigues. The final system was a subtropical depression that intensified south of Madagascar, becoming extratropical on 16 April to end the season.
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Season forecast and summary
On 22 October 2010, the MMS released their seasonal outlook and predicted that there would be 8–10 named storms within the basin during the season. At the end of December, the MMS issued an updated seasonal outlook, predicting that only 6–8 named storms would develop.
As the season began, strong La Niña conditions persisted across the Pacific and Indian oceans, causing an increase in cyclonic flow near the equator over the Indian Ocean. However, atmospheric conditions over the basin significantly decreased tropical cyclogenesis. The Walker circulation – a broad atmospheric circulation – caused unusually moist conditions in the eastern Indian Ocean while producing an increase in subsidence and unusually dry conditions in the western Indian Ocean. In addition, sea surface temperatures were below normal from 5°–15° S and west of 90° E, which limited storm formation near the Chagos Archipelago, typically a common area of formation. By the end of the season, there were only three named storms, the fewest in 50 years, although there was also a subtropical cyclone with gale-force winds that could have been named. In terms of total days in which cyclones were active, the season was slightly behind the 1982–83 season, thus making the 2010–11 season the second-quietest on record. The season also marked a global trend of decreasing tropical cyclone activity over the preceding five years, although the basin experienced a sudden shift toward increased activity in the subsequent season.
Météo-France's meteorological office in Réunion (MFR) – the official Regional Specialized Meteorological Center for the South-West Indian Ocean – tracked and named all tropical cyclones from the east coast of Africa to 90° E. The Joint Typhoon Warning Center (JTWC), which is a joint United States Navy – United States Air Force task force that issues tropical cyclone warnings for the region, also issued advisories for storms during the season.
Systems Tropical Depression 01
For two days toward the end of October, an area of convection persisted within the equatorial trough, east-southeast of the Chagos Archipelago. With a ridge to the south, the system moved generally southwestward. Initially, strong wind shear exposed the circulation, although the system had good inflow from the south. At 12:00 UTC on 25 October, the MFR designated the system as Tropical Disturbance 01, and on the next day upgraded it to a tropical depression, estimating winds of . Also on 26 October, the JTWC classified the system as Tropical Cyclone 01S about 1,575 km (980 mi) east-southeast of Diego Garcia, estimating peak winds of , or a minimal tropical storm. This followed a decrease in wind shear and an increase in convection over the center. Persistent wind shear prevented the system from organizing, causing the thunderstorms to be removed from the center. The JTWC discontinued advisories on the cyclone on 27 October, and on the same day the MFR downgraded it to a tropical disturbance. On 29 October, the MFR issued their final advisory on the system. The remnants continued to the west-southwest, occasionally producing thunderstorms through early November.
Tropical Cyclone Abele
On 23 November, an area of convection persisted southwest of Sumatra within the Intertropical Convergence Zone (ITCZ), accompanied by a poorly defined circulation. Initially the system remained nearly stationary, although it began drifting to the southwest due to a weakness in the subtropical ridge. Decreasing wind shear and improved inflow favored further development. On 28 November, the MFR designated the system as a zone of disturbed weather in the far northeastern portion of the basin. Early the next day, the agency upgraded the system to Tropical Disturbance 02 after the convection organized further. Also on 29 November, the TCWC Perth classified the disturbance as Tropical Low 02U, and the JTWC designated it as Tropical Cyclone 03S about 1,295 km (805 mi) west of the Cocos (Keeling) Islands.
After the storm's development, the convection pulsed around the circulation, and was initially disrupted by wind shear in the region. Despite the circulation being exposed from the thunderstorms, the MFR upgraded the disturbance to a depression on 30 November, and further to Moderate Tropical Storm Abele on 1 December. By that time, the convection had consolidated over the center, which developed an eye amid lower wind shear. The MFR upgraded Abele to a severe tropical storm and later a tropical cyclone on 2 December, estimating peak 10 minute winds of . The JTWC assessed 1 minute winds of . By that time, Abele had turned to the south and southeast ahead of an approaching trough. Cooler water temperatures and increased wind shear caused the convection to weaken, and the winds dropped accordingly. Late on 2 December, Abele crossed 90°E into the Australian region; the storm continued weakening and later became extratropical on 4 December, dissipating the next day.
Tropical Depression 03
On December 28, the ITCZ spurred an increase in convection in the northeastern portion of the basin. An elongated low-pressure area developed by 31 December, accompanied by intermittent thunderstorms. The system slowly consolidated, and the circulation center was exposed but well-defined. Despite moderate wind shear, the convection organized into rainbands on the system's southern periphery. On 2 January, the MFR classified the system as Tropical Disturbance 03, and later that day upgraded it to a tropical depression. However, persistent shear caused the convection to diminish on 3 January, which exposed the circulation. As a result, the MFR discontinued advisories on the system that day. The remnants produced scattered convection while moving west-southwestward. By 10 January, the circulation was still observed, although it was difficult to track. Two days later, the system turned southward, and by 15 January, the convection became more persistent as the system approached northeastern Madagascar. That day, the JTWC issued a Tropical Cyclone Formation Alert based on the improved appearance on satellite imagery. At around 05:00 UTC on 16 January, the remnants of the depression struck Madagascar near Fenoarivo Atsinanana, and the system rapidly dissipated over land.
Tropical Cyclone Bingiza
A zone of disturbed weather developed on 6 February well northeast of Madagascar. For the next few days, the system meandered southwestward, becoming Tropical Disturbance 05 on 8 February. By late the next day, the system had intensified into Moderate Tropical Storm Bingiza, and the JTWC classified it as Tropical Cyclone 13S. After two days of meandering without strengthening, the storm turned to the southwest on 12 February due to a ridge to the south building toward Madagascar, Later that day an eye became apparent on satellite imagery, and Bingiza intensified to tropical cyclone status. Early on 13 February, the cyclone attained peak 10 minute winds of , and the JTWC estimated peak 1 minute winds of . The cyclone moved ashore in northeastern Madagascar on 14 February and quickly weakened as it crossed the country. It emerged into the Mozambique Channel as a weak tropical disturbance, but almost immediately turned southward and moved ashore western Madagascar. The storm again reached open waters on 16 February, and briefly reintensified into a tropical storm. On 17 February, Bingiza made its final landfall near Morondava, and once again weakened over land. Late on 18 February the system reached open waters, which became extratropical two days later.
Cyclone Bingiza was the only main storm to affect Madagascar during the season. It dropped heavy rainfall, peaking at , in addition to the strong winds near the landfall point. In Vinanivao, located along the Masoala peninsula, the cyclone destroyed half of the buildings as well as the roads and bridges, leaving it only accessible by boat. The high winds caused heavy crop damage, including to rice and banana, which left minimal food supplies in some areas. Overall, the cyclone destroyed 405.23 km2 (156.46 mi2) of rice fields, as well as 101.67 km2 (39.26 mi2) of other crops. Across its path, Bingiza destroyed 25,464 houses and damaged 36 schools, and caused 34 deaths in the country. The storm's outer circulation also dropped heavy rainfall in the Comoros, peaking at in the capital Moroni, and increased moist air over Malawi, Mozambique, and Tanzania.
Moderate Tropical Storm Cherono
On 10 March, Tropical Low 23U developed in the Australian basin southwest of Sumatra, and proceeded to move west. After crossing 90ºE, the MFR classified the system as a zone of disturbed weather late on 13 March, followed by an upgrade to Tropical Disturbance 07 on 14 March. The system had a poorly defined circulation but persistent convection, despite strong easterly wind shear. By 16 March however, the shear had relaxed, allowing the convection to organize as the circulation became better defined. Good outflow and warm waters favored further intensification. At 00:00 UTC on 17 March, the MFR upgraded the system to a tropical depression, and a few hours later, the JTWC initiated advisories on the system as Tropical Cyclone 18S about 925 km (575 mi) southeast of Diego Garcia, an island in the central Indian Ocean.