The 1991 Bangladesh cyclone (IMD designation:BOB 01, JTWC designation:02B) was among the deadliest tropical cyclones on record. On the night of 29 April 1991 a powerful tropical cyclone struck the Chittagong district of southeastern Bangladesh with winds of around 250 km/h (155 mph). The storm forced a 6-metre (20 ft) storm surge inland over a wide area, killing at least 138,000 people and leaving as many as 10 million homeless.
During April 22, 1991, an area of westerly winds and persistent cloudiness within the equatorial regions of the North Indian Ocean spawned a large tropical disturbance over the Bay of Bengal. The system was subsequently declared a depression by the India Meteorological Department (IMD) early on April 24, as the cloud mass associated with the system encompassed most of the Bay.
The tropical storm continued slowly northwestward, slowly strengthening to a cyclone-strength storm on the 27th. The cyclone moved between a high pressure system to its northwest and east, and as mid-level westerlies met up with the storm, the cyclone moved northeastward. The westerlies enhanced upper level outflow, and in combination with warm water temperatures the cyclone steadily strengthened to a major hurricane on the 28th.
On the 28th and 29th, as the system increased its speed to the north-northeast, the cyclone rapidly intensified to 1-minute sustained winds of 160 mph (260 km/h), the equivalent to a Category 5 hurricane. Late on the 29th, Cyclone 02B made landfall a short distance south of Chittagong as a slightly weaker 155 mph (250 km/h) Category 4 cyclone. The storm rapidly weakened over land, and dissipated on the 30th over southeast Asia.
At least 138,000 people were killed by the storm, with around 25,000 dead in Chittagong, 40,000 dead in Banshkali and 8,000 dead in Kutubdia . Most deaths were from drowning, with the highest mortality among children and the elderly. Although cyclone shelters had been built after the 1970 Bhola cyclone, many had just a few hours of warning and did not know where to go for shelter. Others who knew about the storm refused to evacuate because they did not believe the storm would be as bad as forecast. Even so, it is estimated over 2 million people did evacuate from the most dangerous areas, possibly mitigating the disaster substantially.
On the island of Sonodia its inhabitants were suffering from diarrhea from drinking contaminated water, respiratory and urinary infections, scabies and various injuries with only rice for food and contaminated drinking water. Out of the ten wells on the island only 5 were functional of which only one providing pure water with the rest contaminated by sea water.
The storm caused an estimated $1.5 billion (1991 US dollars) in damage. The high velocity wind and the storm surge devastated the coastline. Although a concrete levee was in place near the mouth of the Karnaphuli River in Patenga, it was washed away by the storm surge. The cyclone uprooted a 100-ton crane from the Port of Chittagong, and smashed it on the Karnaphuli River Bridge, effectively breaking it into two partitions. A large number of boats and smaller ships ran aground. Bangladesh Navy and Bangladesh Air Force, both of which had bases in Chittagong, were also heavily hit. The Isha Khan Naval Base at Patenga was flooded, with heavy damages to the ships. Most of the fighter planes belonging to the air force were damaged. Approximately 1 million homes were destroyed, leaving about 10 million people (a substantial portion of Bangladesh's population) homeless. The extensive damage caused the price of building materials to greatly increase.
The storm surge subsequently caused the embankment, as well as whole villages, to be swept away. For an additional three to four weeks after the storm had dissipated, mass land erosion resulted in more and more farmers losing their land, and therefore, the number of unemployed rose. In several areas up to 90 percent of crops had been washed away. The shrimp farms and salt industry were left devastated.
The United States amphibious task-force, consisting of 15 ships and 2,500 men, returning to the US after the Gulf War was diverted to the Bay of Bengal to provide relief to an estimated 1.7 million survivors. This was part of Operation Sea Angel, one of the largest military disaster relief efforts ever carried out, with the United Kingdom, China, India, Pakistan and Japan also participating.
Operation Sea Angel began on May 10, 1991, when President Bush directed the US military to provide humanitarian assistance. A Contingency Joint Task Force under the command of Lieutenant General Henry C. Stackpole, consisting of over 400 Marines and 3,000 sailors, was subsequently sent to Bangladesh to provide food, water, and medical care to nearly two million people. The efforts of U.S. troops, which included 3,300 tons of supplies, are credited with having saved as many as 200,000 lives. The relief was delivered to the hard-hit coastal areas and low-lying islands in the Bay of Bengal by helicopter, boat and amphibious craft.
The US military also provided medical and engineering teams to work with their Bangladeshi counterparts and international relief organisation to treat survivors and contain an outbreak of diarrhea, caused by contaminated drinking water. Water purification plants were built and prevalence of diarrhea amongst the population was reduced to lower than pre-cyclone levels.
After the departure of the task force, 500 military personal, two C-130 cargo planes, five Blackhawk helicopters and four small landing craft from the task force remained to help finish off relief operations in outlying districts and rebuild warehouses. The amphibious landing ship USS St. Louis (LKA-116) delivered large quantities of intravenous solution from Japan to aid in the treatment of cyclone survivors.
As a result of the 1991 cyclone, Bangladesh improved its warning and shelter systems. Also, the government implemented a reforestation program to mitigate future flooding issues.