Tropical Cyclone Bijli came ashore over eastern Bangladesh on April 17, 2009. The storm caused little damage, according to news reports, but did dump heavy rain on Bangladesh and neighboring Burma (Myanmar). This image, made with data captured by the Tropical Rainfall Measuring Mission (TRMM) satellite on April 17, shows the rainfall associated with the storm.

As much as 50 millimeters of rain fell per hour in the regions where rainfall was heaviest, shown in red. Outside the area of concentrated heavy rain, the rainfall was relatively light, as shown by the wide field of blue. The measurements shown in this image are from a variety of sensors on the TRMM satellite. Rain rates in the center of the swath (lighter area) are from the TRMM Precipitation Radar, the first precipitation radar in space, and those in the outer part of the swath are from the TRMM Microwave Imager. The rain rates were overlaid on infrared data from the TRMM Visible Infrared Scanner.

Designed to measure rainfall from space, the Tropical Rainfall Measuring Mission satellite has been in service for over 11 years and continues to provide valuable images and information on tropical cyclones around the tropics using a combination of passive microwave and active radar sensors

PASADENA, Calif. – A “pre-existing condition” in the North Indian Ocean stoked the sudden intensification of last year’s Tropical Cyclone Nargis just before its devastating landfall in Burma, according to a new NASA/university study. The cyclone became Burma’s worst natural disaster ever and one of the deadliest cyclones of all time.

Scientists at the National Taiwan University, Taipei; and NASA’s Jet Propulsion Laboratory, Pasadena, Calif., used data from satellite altimeters, measurements of ocean depth and temperature and an ocean model to analyze the ocean conditions present at the time of the catastrophic storm. Nargis intensified from a relatively weak category 1 storm to a category 4 monster during its final 24 hours before making landfall on May 2, 2008.

Lead author I-I Lin of National Taiwan University and her team found the ocean conditions Nargis encountered created the perfect recipe for disaster. Cyclones thrive on warm layers of ocean water that are at least 26 degrees Celsius (79 degrees Fahrenheit). As they traverse the ocean, they typically draw deep, cold water up to the ocean surface, a process that limits their ability to strengthen, and even weakens them as they evolve. However, Nargis passed over a pre-existing warm ocean feature in the Bay of Bengal where upper ocean warm waters extended deeper than normal, from 73 to 101 meters (240 to 331 feet).

“This abnormally thick, warm water layer, which formed about a month earlier, kept deeper, colder waters from being drawn to the surface, increasing the energy available to fuel Nargis’ growth by 300 percent,” said Lin. “Combined with other atmospheric conditions conducive to strengthening, this warm ocean feature allowed Nargis to reach speeds of 115 knots [213 kilometers, or 132 miles, per hour] at landfall. Had Nargis not encountered this warm ocean feature, it would likely not have had sufficient energy to intensify rapidly.”

Lin said the research will contribute to improving our understanding of and ability to forecast catastrophic events like Nargis in the future, reducing loss of life and property. “Such a capability is particularly needed in developing countries, where less advanced cyclone monitoring and warning systems can leave people with little time to escape from disaster,” she said.