In this image, note the huge rainfall footprint produced by Tropical Cyclone 01B as it intensified over the Bay of Bengal. (Here is another, true-color image of the cyclone as it approached the coast of Myanmar in southeast Asia on May 19, 2003.) At first, it would appear that the isolated rainfall pocket located over Sri Lanka bears little relation to the burgeoning tropical storm. However, there is evidence to suggest that the rainstorms that deluged Sri Lanka were associated with an outer “feeder band” of moisture entering the tropical cyclone from the southwest.

The Tropical Rainfall Measuring Mission (TRMM) features a spaceborne weather radar built by the Japanese space agency NASDA. In operation for five years, TRMM has provided unprecedented views of tropical rain events around the globe, and now also provides information on flash flood potential (accessed by visiting the TRMM Web site at http://trmm.gsfc.nasa.gov).