2011-12 South-West Indian Ocean cyclone season

The 2011–12 South-West Indian Ocean cyclone season is an event in the annual cycle of tropical cyclone formation. It began on November 15, 2011, and will end on April 30, 2012, with the exception for Mauritius and the Seychelles, for which it will end on May 15, 2012. These dates conventionally delimit the period of each year when most tropical cyclones form in the basin, which is west of 90°E and south of the Equator. Tropical cyclones in this basin are monitored by the Regional Specialised Meteorological Centre in Réunion.

Severe 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 Mauritus Meteorological service naming it Alenga. Continuing to rapidly intensify, Alenga strengthened into a severe tropical storm later that day.

Storm names
Within the South-west Indian Ocean, Tropical Depressions and Subtropical Depressions that are judged to have 10-minute sustained windspeeds of 65 km/h, (40 mph) by the Regional Specialized Meteorological Center on La Réunion Island, France (RSMC La Réunion) are usually assigned a name. However it is the Sub-Regional Tropical Cyclone Advisory Centers in Mauritius and Madagascar who name the systems. The Sub-Regional Tropical Cyclone Advisory Center in Mauritius names the storm should it intensify into a moderate tropical storm between 55°E and 90°E, if the storm should intensify into a moderate tropical storm between 30°E and 55°E then the Sub-Regional Tropical Cyclone Advisory Center in Madagascar assigns the appropriate name to the storm. For the final year, tropical cyclones that move into this region from the Australian region will be renamed by the Sub-Regional Tropical Cyclone Advisory Center in Mauritius, however tropical cyclones moving into the Australian region will not be renamed. New name lists are used every year, whilst a name is normally only used once so thus no names are retired.

Season effects
This table lists all the storms that developed in the Southern Hemisphere during the 2011–2012 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 in 2012 USD.