CYCLONES OF SOUTH ASIA: BAY OF BENGAL, TRACKS, DEADLIEST STORMS EVER

CYCLONES

NOAA satellite imagery of 1999 Orissa Cyclone 05B located in the Bay of Bengal east of India.

In April through June and from October through November, tropical cyclones, accompanied by high seas and heavy flooding, occur. Cyclones are defined a storm with winds exceeding 75 mph. About five cyclones a year strike the Bay of Bengal, which stretches from the Bangladesh coast in the North to the latitude of southern Sri Lanka in the south, and from the Indian coast in the west to Myanmar and the Andaman and Nicobar Islands. Cyclones are usually associated with the Bay of Bengal but they can also occur in the Arabian Sea.

Tropical cyclones are warm-core, low pressure systems without any "front" attached, that develop over the tropical or subtropical waters, and have an organized circulation. Depending upon location, tropical cyclones have different names around the world. 1) In the Atlantic and Eastern Pacific Oceans they are called Hurricanes. 2) In the Western Pacific they are called Typhoons. 3) In the Indian Ocean they are called Cyclones. Indian ocean

Cyclones strike South Asia and the Indian subcontinent along two primary ocean basins, with the Bay of Bengal generating approximately 4 times more storms than the Arabian Sea. Eastern South Asia bears the brunt of the activity, with a majority of systems developing in the Bay of Bengal striking states like Odisha, West Bengal, Andhra Pradesh, Tamil Nadu and Bangladesh. Western South Asia sees significantly less activity, typically experiencing one out of every two to four storms that strike India. The majority of Arabian Sea cyclones hit the Gujarat and Maharashtra coasts. [Source: Wikipedia. India Water Portal]

How Cyclones Are Generated and Powered

Cyclonic storms form when large masses of air begin rotating at high speed around a low-pressure area. They are fueled by warm water in the bay and often follow a track that brings them right to Bangladesh, [Source: “Depressions and Cyclones”Inter Sector Coordination Group, May 13, 2019]

different names for cyclones in different parts of the world

Tropical cyclones are powered by heat from the sea. They are products of a warm tropical ocean and a warm, moist atmosphere. Hurricanes are typically steered by easterly winds, generally south of 25 degrees north latitude and by high-level westerly winds north of 25 degrees north latitude.

There are several favorable environmental conditions that must be in place before a tropical cyclone can form. They are: 1) Warm ocean waters (at least 80°F, 27°C) throughout a depth of about 46 meters (150 feet). 2) An atmosphere which cools fast enough with height such that it is potentially unstable to moist convection. 3) Relatively moist air near the mid-level of the troposphere (4,900 meters, 6,000 feet). 4) Generally a minimum distance of at least 480 kilometers (300 miles) from the equator. 5) A pre-existing near-surface disturbance. 6) Low values (less than about 23 mph, 37 kph) of vertical wind shear between the surface and the upper troposphere. Vertical wind shear is the change in wind speed with height.

Cyclones in the Bay of Bengal

"Cyclone" is the name given to a hurricane-like storm when it occurs in the northern Indian Ocean or the Bay of Bengal. Known as typhoons in much of East Asia and hurricanes in the Western hemisphere, they are large-scale rotating storms that generate high winds and typically form at sea before moving inland. Most cyclones in the northern hemisphere hit the Bay of Bengal between Bangladesh and the east coast of India.

Cyclones in the Bay of Bengal affect eastern India, Bangladesh and Myanmar. The region accounts for a disproportionate share of global cyclonic activity and storm-related casualties due to warm waters and a unique funnel-shaped geography. Tropical cyclones in the Bay of Bengal generally head to India and Bangladesh not Myanmar.[Source: IPE Global}

Severe Cyclonic Storm Remal making landfall
in the Ganges Delta on May 26, 2024 Several geographical and atmospheric factors make this basin particularly volatile.Sea surface temperatures consistently remain above 28°C (82°F), the threshold required to sustain tropical cyclones. The V-shape of the Bay forces storm surges and atmospheric activity to concentrate toward the northern coasts, amplifying wind speeds and tidal damage during landfall. Massive freshwater inflow from major rivers (like the Ganges and Brahmaputra) keeps the top layer of the ocean less saline. This freshwater prevents the warmer surface water from mixing with deeper, cooler water, maintaining the intense heat needed to fuel storms.

Historically, the Bay of Bengal is responsible for a vast majority of the world's cyclone-related fatalities, largely due to dense coastal populations in India and Bangladesh. In recent years, climate patterns have caused a shift in these seasons, yielding stronger, more intense pre-monsoon super-cyclones as surface temperatures continue to rise.

Cyclone Season in the Bay of Bengal

The cyclone season in the northern hemisphere is from June to October. Cyclones are most likely to strike in the spring and fall. The cyclone season in the Bay of Bengal spans two primary periods: the pre-monsoon season from April to early June and the highly active post-monsoon season from October to December. While the number of cyclones before the summer monsoon. is lower than in the post-monsoon period, they are often extremely powerful and destructive. These storms generally track northward, making landfall on the eastern coast of India, Bangladesh, or Myanmar. [Source: IPE Global}

The Post-Monsoon Season (October–December) is the primary cyclone season, seeing nearly double the frequency of severe storms compared to the pre-monsoon. The retreating monsoon creates perfectly stagnant winds and low-pressure zones, producing peak activity in October and November.

Cyclonic activity drops significantly between June and September, the heart of the monsoon season. While low-pressure systems form during the monsoon, strong vertical wind shear tears them apart before they can organize into severe tropical cyclones.

Storms and typhoons originating in the Pacific Ocean often track westward across the South China Sea, entering the Bay of Bengal through the Strait of Malacca to re-intensify. The typhoon season in the Pacific is from June to October.

Cyclone Damage

Cyclone Hudhud destruction in Visakhapatnam, Andhra Pradesh, India on October 14, 2014

Cyclones are large storm systems affecting weather conditions well beyond their center before, during and after landfall. Cyclones have destructive winds but the most of the damage is caused by water and rain. The most devastating "super-cyclones" pack 200 kph winds, hit at high tide and stall over one area. The islands in the Bay of Bengal usually the hardest hit. They are densely populated with fishermen and rice farmers. After the cyclones go they often leave believed salt contaminations

Hazards associated with depressions and cyclones include: 1) Strong winds — between 62 and 200 km/hour in the cyclone itself; 2) Heavy rainfall — with potential to trigger landslides and flash floods; 3) Storm surge — mounds of seawater driven towards the shore due to winds, wave and pressure. [Source: “Depressions and Cyclones”Inter Sector Coordination Group, May 13, 2019]

Although cyclones are well known for their strong and destructive winds, a cyclone’s storm surge is by far the greatest threat to life and property along the immediate coast. Storm surge is simply water that is pushed toward the shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the storm tide, which can increase the mean water level five meters or more. In addition, wind driven waves are superimposed on the storm tide. This rise in water level can cause severe flooding in coastal areas, particularly when the storm tide coincides with the normal high tides. Because much of India’s densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level, the danger from storm tides is tremendous.

South Asia and Bay of Bengal Cyclone Tracks

Bay of Bengal Cyclone Tracks Tropical cyclones in the Bay of Bengal usually move toward the north, northwest, or north-northeast. Their paths are influenced by warm sea surface temperatures, seasonal wind patterns, and the funnel-shaped coastline of the northern Bay of Bengal, which can intensify storm surges. Most cyclones develop during the pre-monsoon season from April to May and the post-monsoon season from October to December. [Source: Researchgate]

Pre-Monsoon Tracks During the pre-monsoon season, cyclones that form in the central or southern Bay of Bengal often move northwestward before curving sharply to the northeast. These storms commonly make landfall along the eastern coast of India, particularly in Odisha and West Bengal, or continue toward Bangladesh or Myanmar.

Post-Monsoon Tracks During the post-monsoon season, cyclones frequently travel west-northwest toward the southeastern coast of India, affecting states such as Tamil Nadu and Andhra Pradesh. Other storms curve north-northeast into the northern Bay of Bengal, where they often strike Bangladesh and the Indian state of West Bengal.

Cyclone Predictions and Warnings

According to one academic paper: It can be difficult to predict the development and path of a cyclone with a high level of certainty until it comes near to the coast. The strength and path of a cyclone is affected by atmospheric conditions, and have been known to turn in unexpected directions. [Source: “Depressions and Cyclones”Inter Sector Coordination Group, May 13, 2019]

Meteorologists run models that project how the cyclone can develop, including possible paths, intensity of wind, rain and storm surge, and when those hazards will affect human settlements. Those models are then compared to see if they tend towards the same projected development or if there are a lot of possible directions the cyclone can move and develop. Because of the chaotic nature of the earth’s atmosphere, certainty is difficult to achieve.

Because of the difficulty in predicting the strength, timing and path of a cyclone, cyclone warnings and advisories mainly come in stages and can change quickly. Meteorological departments issue advisories when they are confident that the information is reliable and actionable. Narrative bulletins from meteorological departments are issued on a running basis and will be dated and numbered. Visual cyclone path projections from meteorological departments are updated on a running basis and will usually show a “cone of uncertainty” around the projected path.

Deadliest Tropical Cyclones Ever

Rank — Name — Areas of Largest Impact — Year — Ocean Area — Deaths
1) Great Bhola Cyclone — Bangladesh — 1970 (Nov 12) — Bay of Bengal — 300,000 - 500,000
2) Hooghly River Cyclone — India and Bangladesh — 1737 — Bay of Bengal — 300,000
3) Haiphong Typhoon — Vietnam — 1881 — West Pacific — 300,000
4) Coringa — India — 1839 — Bay of Bengal — 300,000

5) Backerganj Cyclone — Bangladesh — 1584 — Bay of Bengal — 200,000
6) Great Backerganj Cyclone — Bangladesh — 1876 — Bay of Bengal — 200,000
7) Chittagong — Bangladesh — 1897 — Bay of Bengal — 175,000
8) Super Typhoon Nina — China — 1975 (Aug 5) West Pacific — 171,000
9) Cyclone 02B — Bangladesh — 1991 (May 5) Bay of Bengal — 138,866
10) Cyclone Nargis — Myanmar — 2008 (May 3) Bay of Bengal — 138,366
Death counts from large killer cyclones are highly uncertain, particulary for those before 1900) The above rankings are somewhat speculative. [Source: wunderground.com]

11) Swatlow — China — 1922 (Jul 27) West Pacific — 100,000
12) Great Bombay Cyclone — India — 1882 — Arabian Sea — 100,000
13) Hakata Bay Typhoon — Japan — 1281 — West Pacific — 65,000
14) Bangladesh — 1942 (Oct 14) Bay of Bengal — 61,000
15) India — 1935 — Bay of Bengal — 60,000
16) Calcutta — India — 1864 — Bay of Bengal — 60,000
17) Barisal — Bangladesh — 1822 — Bay of Bengal — 50,000
18) Sundarbans coast — Bangladesh — 1699 — Bay of Bengal — 50,000
19) India — 1833 — Bay of Bengal — 50,000
20) India — 1854 — Bay of Bengal — 50,000

21) Wenchou — China — 1912 (Aug) West Pacific — 50,000
22) Bengal Cyclone — Calcutta — India — 1942 — Bay of Bengal — 40,000
23) Bangladesh — 1912 — Bay of Bengal — 40,000
24) Bangladesh — 1919 — Bay of Bengal — 40,000
25) Canton — China — 1862 — West Pacific — 37,000
26) Bangladesh — 1965 (May 11) Bay of Bengal — 36,000
27) Backerganj (Barisal) Bangladesh — 1767 — Bay of Bengal — 30,000
28) Barisal — Bangladesh — 1831 — Bay of Bengal — 22,000
29) Great Hurricane — Lesser Antilles Islands — 1780 — Atlantic — 22,000
30) Chittagong — Bangladesh — 1963 (May 28) Bay of Bengal — 22,000
31) Great Coringa Cyclone — India — 1789 — Bay of Bengal — 20,000
32) Nagasaki Typhoon — Japan — 1828 — Western Pacific — 15,000
33) Urir — Bangladesh — 1985 (May 28) Bay of Bengal — 15,000
33) Tacloban — Philippines — November 1912 — Western Pacific — 15,000
35) Devi Taluk — Southeast India — 1977 (Nov 12) Bay of Bengal — 14,204
36) Bangladesh — 1965 (May 31) Bay of Bengal — 12,047

Image Sources: Wikimedia Commons

Text Sources: “Encyclopedia of World Cultures Volume 3: South Asia,” edited by Paul Hockings, 1992, National Geographic, Ministry of Tourism, Government of India,, CIA World Factbook, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Encyclopedia.com, Library of Congress, Live Science, The Conversation, The New Yorker, Time, BBC, CNN, Reuters, Associated Press, AFP, Lonely Planet Guides, Google AI, Wikipedia, The Guardian and various websites, books and other publications.

Last updated June 2026