The 1991 Bangladesh cyclone was among the deadliest tropical cyclones on record. Forming out of a large area of convection over the Bay of Bengal on April 24, the tropical cyclone initially developed gradually while meandering over the southern Bay of Bengal. On April 28, the storm began to accelerate northeastwards under the influence of the southwesterlies, and rapidly intensified to super cyclonic storm strength near the coast of Bangladesh on April 29. After making landfall in the Chittagong district of southeastern Bangladesh with winds of around , the cyclone rapidly weakened as it moved through northeastern India, degenerating into a remnant low over the Yunnan province in western China.
One of the most powerful tropical cyclones ever recorded in the basin, the tropical cyclone caused a 6.1 m (20 ft) storm surge, which inundated the coastline, causing at least 138,866 deaths and about US$1.7 billion (1991 USD) in damage. As a result of the catastrophic damage, the United States and other countries carried out Operation Sea Angel, one of the largest military relief efforts ever carried out.
Meteorological history
On April 22, 1991, a circulation formed in the southern Bay of Bengal from a persistent area of convection, or thunderstorms, near the equator in the eastern Indian Ocean. Within two days, the cloud mass encompassed most of the Bay of Bengal, focused on an area west of the Andaman and Nicobar Islands. On April 24, the India Meteorological Department (IMD) designated the system as a depression, and the Joint Typhoon Warning Center (JTWC) labeled the system as Tropical Cyclone 02B. Ships in the region reported winds of around around this time.
From its genesis, the storm moved northwestward, and early forecasts from the JTWC anticipated that trajectory would continue toward Andhra Pradesh in southeastern India, due to a westward-moving ridge over India. The cyclone gradually strengthened, amplified by a wind surge from the south. The IMD upgraded the depression to a cyclonic storm on April 25, and to a severe cyclonic storm on the following day. By April 26, wind shear had decreased to near zero as an anticyclone developed aloft the hurricane. Around this time, the cyclone rounded the western periphery of a large subtropical ridge over Thailand, and the storm turned northward between the ridge to the northeast and northwest. The IMD upgraded the system to a very severe cyclonic storm on April 27, estimating winds of 142 km/h (89 mph). By this time, the JTWC anticipated a future track toward the Ganges Delta region of eastern India and Bangladesh.
On April 28, the flow of the southwesterlies caused the cyclone to accelerate to the north-northeast. This flow also amplified the storm's outflow, and the cyclone intensified further. By 12:00 UTC on April 28, or about 31 hours before landfall, the JTWC was correctly forecasting a landfall in southeastern Bangladesh. Early on April 29, the IMD upgraded the system to a super cyclonic storm – the highest category – and estimated peak winds of . The JTWC estimated peak winds of , the equivalent to a Category 5 hurricane on the Saffir–Simpson scale or a super typhoon. The IMD also estimated a minimum barometric pressure of , while the JTWC estimated a minimum pressure of . The cyclone's high winds and low pressure, a rarity for the Bay of Bengal, ranked it among the most intense cyclones in the basin. At 19:00 UTC on April 29, the cyclone made landfall about 55 km (35 mi) south of Chittagong in southeastern Bangladesh while slightly below its peak strength. Moving through the mountainous terrain of the Chittagong Hill Tracts, the cyclone quickly weakened and crossed into northeast India, where it degenerated into a remnant low-pressure area.
Background and preparations
Until 2004, tropical cyclones were not named in the north Indian Ocean. Through its role as Regional Specialized Meteorological Center, the IMD issued warnings on the storm, designating it Super Cyclonic Storm BoB 1. The agency tracked the storm using satellite imagery, radar, and other meteorological stations. The JTWC, providing warnings and support to American military interests, designated the storm as Tropical Cyclone 02B, and also referred to it as a "super cyclone". Although the cyclone was officially unnamed, documents from the United States Agency for International Development and the United States Army referred to the storm as Cyclone Marian. Time magazine referred to the storm as Cyclone Gorky.