|Category 3 severe tropical cyclone (AUS)|
|Category 2 tropical cyclone (SSHS)|
|Duration||3 December – 9 December|
|Intensity||150 km/h (90 mph) (10-min), 968 mbar (hPa)|
Tropical Cyclone Alenga was a strong cyclone that formed in the 2011-12 South-west Indian Ocean and Australian region cyclone seasons. It attained peak intensity on 8 December with 10-min sustained winds of 90 mph.
On 3 December, TCWC Perth and TCWC Jakarta reported that a tropical low had developed about 1220 km (760 mi) to the southwest of Jakarta, Indonesia. Over the next few days the low moved towards the southeast while the systems low level circulation centre gradually developed further in an area of moderate vertical windshear. During the next day the low moved out of the Australian region and moved into the South-West Indian Ocean, where it was named Alenga by the Mauritius Meteorological Service during 5 December. During that day, RSMC La Reunion reported that Alenga reached an initial 10-minute peak windspeeds of intensity of 100 km/h (65 mph), as it started to recurve and move towards the Australian region. The system then weakened slightly before re-intensifying and surpassing its initial peak intensity, as it moved back into the Australian region during 7 December. Later that day, the JTWC reported that Alenga had become equivalent to a category one hurricane on the Saffir-Simpson Hurricane Wind Scale (SSHWS). During the next day, TCWC Perth reported that Alenga had become a Category 3 Severe Tropical Cyclone and reached its 10-minute peak windspeeds of 150 km/h (90 mph) before the JTWC also reported that Alenga had intensified further and peaked with 1-minute windspeeds of 175 km/h (110 mph) and become equivalent to a category 3 tropical cyclone on the SSHWS. Alenga then started to rapidly weaken as it moved into an area of higher vertical windshear, with convection diminishing and the low level circulation centre becoming elongated. On 9 December, TCWC Perth reported that Alenga had degenerated into a tropical low while the JTWC followed suite and issued their final advisory on Alenga. TCWC Perth tracked the remnants of Alenga, for another 2 days before issuing their final advisory on 11 December.
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