Aila recently became the first cyclone of the 2009 cyclone season in the North Indian Ocean just before making landfall in far eastern India in the northern Bay of Bengal. So far the storm is being blamed for 275 deaths in India and Bangladesh, but more are expected. Tropical Storm Bijli, which made landfall in eastern Bangladesh, was the first and only other named storm of the season back in mid April. Although the cyclone season in the North Indian Ocean is long, stretching from April through December, there are typically just over 5 named storms per year with 2 becoming full tropical cyclones.

Aila evolved from a tropical disturbance in the central Bay of Bengal. The disturbance slowly organized over a period of 2 to 3 days and became a tropical storm on the morning (local time) of May 23rd as it moved northward. The Tropical Rainfall Measuring Mission satellite (known as TRMM) was placed into service in November of 1997. From its low-earth orbit, TRMM can provide valuable images and information on tropical cyclones around the Tropics using a combination of passive microwave and active radar sensors.

The first image shows Aila just as it was becoming a tropical storm. The image was taken at 21:20 UTC 23 May 2009 (2:50 am 24 May local time) and shows the horizontal pattern of rain intensity within the storm. Rain rates in the center swath are from the TRMM Precipitation Radar (PR), the first precipitation radar in space, while rain rates in the outer swath are from the TRMM Microwave Imager (TMI). The rain rates are overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS). At this stage, the center is not very well defined; however, the developing cyclonic circulation is evident by the curvature in the rain bands. Aila would officially became a tropical storm less than 3 hours after this image was taken.