Cyclone Aila (RSMC Designation: BOB02, JTWC Designation: 02B, also known as Severe Cyclonic Storm Aila) was the second tropical cyclone to form within the Northern Indian Ocean during 2009. The disturbance that was to become Cyclone Aila formed on 21 May 2009 about 950 kilometres (590 mi) to the south of Kolkata, in India. Over the next couple of days the disturbance slowly developed before a Tropical Cyclone Formation Alert was issued by the Joint Typhoon Warning Center early on 23 May 2009 and being designated as a depression by RSMC New Delhi. As of 27 May 2009, 330 people have been killed by Aila and at least 8,208 more are missing, while about 1 million are homeless. Health officials in Bangladesh confirmed a deadly outbreak of diarrhea on 29 May, with more than 7,000 people being infected and four dying. In Bangladesh, an estimated 20 million people were at risk of post-disaster diseases due to Aila. Damage totaled $40.7 million (USD).
The Sunderbans, a region which houses 265 of the endangered Bengal Tigers, was inundated with 6.1 m (20 ft) of water. Dozens of the tigers are feared to have drowned in Aila's storm surge along with deers and crocodiles. As of 27 May 2009, one tiger has been found alive; it was found in a waterlogged cowshed following the cyclone's landfall. Additionally the forest remains under an estimated 2.4 m (7.9 ft) of water. On 27 May, conservationists have begun a search for the tigers throughout the forest. The search teams were supplied with fresh drinking water for the tigers as their natural water source was inundated with salt water from Aila's storm surge.