Severe Weather in Bangladesh

There are multiple steps to a tornado forming. The first object that appears is a rotating body of air at the ground that forms because of wind sheer. The wind speeds are higher with altitude and drag and friction on the ground cause the air on the ground to move more slowly. The horizontal rotating air is lifted off the ground by the updraft of a thunderstorm. Once the rotating column of air is nearly vertical it is considered a mesocyclone. The mesocyclone is then fully developed in the updraft of the thunderstorm.  A funnel cloud then descends from the slowly rotating “wall cloud” and as soon as the funnel cloud touches ground it is considered a tornado. In the United States most tornadoes travel from southwest to northeast. This happens because the warm, moist air from the gulf meets the cool, dry air from Canada, and you add in a dry breeze from the Rockies, and thunderstorms are formed. On average there are 1,253 tornadoes observed in the United States (source). These usually stretch in a moving band bowing from Texas to the great lakes. Tornadoes also occur in Bangladesh, and on average 179 tornadoes are observed each year, yet the average deaths due to tornadoes is the highest in the world (source). The country of Bangladesh is located right in a tornado hot spot next to the Himalayan Mountains, see map below.

http://www.pbs.org/wgbh/nova/earth/tornado-country.html

 It appears that tornadoes observed has increased over the last 30 years. There is evidence showing that global warming has case an increase in very heavy precipitation events. Knowing that tornadoes form in extreme thunderstorms, global warming could be a cause for the increase in tornado occurrence. With the temperature in the tropics getting warmer, warmer temperatures coming from the south and forming a low pressure area with cold temperatures coming from the north could be causing more thunderstorms, and therefore more tornadoes.

There are three things required in order for a hurricane to form; warm ocean temperatures, deep warm ocean layer, and the Coriolis Effect. Bangladesh has the warm water of the Indian Ocean, which is near the equator and evenly heated by the sun causing a deep warm ocean layer, and obviously the Coriolis Effect is present. There are three main regions where hurricanes form, and they have a different name in each region. In the Atlantic and East Pacific region they are called Hurricanes, in the Indian Ocean and Australia region they are called Cyclones, and in the coast of China and Indonesia they are called Typhoons (see map below).

http://www.learnnc.org/lp/editions/nchist-recent/6248

In the United States the hurricanes come from the Atlantic Ocean in the east, makes landfall on the east coast, and after making landfall friction caused by the large land mass and its terrain cuts off the hurricane's circulation, and squeezes out the storm's moisture. The storm being weakened results in the hurricane forming a C shape and eventually brings them over cold waters which causes dissipation. On average the United States experiences 6 hurricanes annually (source). Bangladesh also experiences hurricanes. The annual average is unclear, however I did find that since 2005 five SEVERE cyclonic storms have hit, and on average a severe cyclonic storm hits the coast of Bangladesh every 3 years (source).