Cyclone Sidr slams into Bangladesh

Tropical Cyclone Sidr made landfall at 1430 GMT in western Bangladesh as a mighty Category 4 storm with 150 mph winds. Sidr is the second strongest cyclone to make landfall in Bangladesh since reliable record keeping began in 1877. The only stronger storm was the 1991 Bangladesh Cyclone, which struck eastern Bangladesh as a Category 5 cyclone. The 30 foot storm surge of that storm killed at least 140,000 people. Sidr is the Arabic word for the jujube tree.


Figure 1. Image of Tropical Cyclone Sidr as a Category 4 storm (928 mb) with 155 mph winds. Image taken at 4:57am EST 11/15/07. The cyclone made landfall at 1430 GMT in the Sundarbans Forest area of Bangladesh, just east of Calcutta, India. Image credit: Navy Research Lab.

Sidr's storm surge
The big killer in Bangladesh cyclones is the storm surge. The triangular shape of Bengal Bay funnels high surges into the apex of the triangle where Bangladesh sits, and the shallow bottom of the bay allows extraordinarily high storm surges to pile up. The maximum theoretical storm surge from a worst-case Category 5 cyclone is thought to be 41 feet in western Bangladesh (Islam, 2006). Sidr's maximum storm surge to the right of where the eye makes landfall is likely to be in the 20-25 foot range. Of critical importance is the timing of landfall with respect to high tide, since there is a 1.5 meter (5 foot) difference between low and high tide in western Bangladesh. According to mobilegeographics.com, high tide is at approximately 1am local time tonight, and Sidr made landfall about halfway between low and high tide. Thus, Bangladesh did have a little luck, as the storm tide could have been about 2-3 feet higher had Sidr hit at high tide.

The coast in western Bangladesh has the Sundarbans Forest, the world's largest forest of mangrove trees. This region is the least populated coastal area in the country, and has been part of a major reforestation effort in recent years. The portion of coast likely to receive the highest storm surge levels of 20-25 feet is virtually unpopulated. However, storm surge levels of 10-20 feet are still likely to affect areas with a population of at least a million, to the east of the Sundarbans forest, and inland from the forest. The last major cyclone to hit western Bangladesh occurred in November 1988. This Category 3 cyclone with 125 mph winds had a 5-10 foot storm surge, and killed 2,000 people.

Hurricane shelters in Bangladesh
Since the Great Bhola Cyclone of 1970, a Category 4 cyclone that brought a storm surge of up to 27 feet and killed an estimated 350,000-550,000 people, Bangladesh embarked on program to build concrete cyclone shelters (Figure 2). After the 1991 cyclone, this process accelerated, thanks in part to foreign assistance. Bangladesh now has over 2500 multi-purpose cyclone shelters that can also be used as primary schools. The warning system in Bangladesh is fairly effective at notifying the population of an approaching cyclone, but many residents choose not to evacuate to the shelters, since most of them are in poor condition with minimum or no maintenance at all (Karim, 2001). In any case, these shelters can accommodate less than 3% of the population of western Bangladesh (Islam, 2006).


Figure 2. A Bangladesh cyclone shelter built after the devastating 1970 cyclone. Image credit: Harry M. Jol, professor at University of Wisconsin, Eau Claire.

The Bangladesh newspaper The Daily Star is already reporting that 300 fishing boats have sunk in Sidr, with 1,000 fishermen missing. While I don't expect we'll see anything approaching the 1991 cyclone with its death toll of 140,000, since Sidr is hitting a relarively unpopulated region of the coast, the storm has the potential to kill several thousand people in Bangladesh. Also of concern is India. The eastern portion of the Calcutta metropolis will receive winds near hurricane force, and these winds could cause major destruction of poorly built housing. Flash flooding from heavy rains could also affect both India and Bangladesh. It's a bad night to be in Bangladesh.

Links to follow for Sidr
Dhaka, Bangladesh current conditions
Calcutta, India current conditions

References

Islam, T., "Integrated Approach to Cyclone Wind Analysis and disaster planning for the Benladesh coast," Ph.D. Dissertation, Texas Tech University, December 2006.

Karim, N., (1999) Options for cyclone protection: Bangladesh context".

Paul, A., and M. Rahman, "Cyclone Mitigation Perspectives in the Islands of Bangladesh: A Case of Sandwip and Hatia Islands", Coastal Management, 34, Issue 2 April 2006, p, pp 199-215.

Jeff Masters