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).

Daily Weather in Bangladesh

As I have mentioned before, the capitol of Bangladesh is the city of Dhaka.  For the city of Dhaka, I have created a three-day weather forecast that will cover Tuesday through Thursday, November 11^th -13^th.  On Tuesday, the forecasted high is 88*F and the forecasted low is 73*F, with a 1% chance of precipitation.  For Wednesday, the forecasted high is 90*F and the forecasted low is 71*F, with a 2% chance of precipitation. Lastly, Thursday is forecasted to have a high of 90*F and a low of 70*F, with a 1% chance of precipitation as well.  The average pressure of the three day period is predicted to be 29.81, and stay relatively the same over the three days.  The average wind speed over the three day period is predicted to be 3.16mph, and stay the same throughout the three day period.

The image above shows clouds, precipitation and weather stations in Bangladesh.  There are a few clouds but they are not very close.  The closest clouds are off the coast of Bangladesh over the Bay of Bengal.   There are a few warm clouds, but the majority of the clouds are cold.   There is no precipitation anywhere near the city of Dhaka or the country of Bangladesh as a whole for that matter.  There aren’t clear defined areas of either vegetation or city. There is however countless areas with rivers and what looks like swamp like environments. This could be a result of lingering water from the monsoon season. There are no mountains nearby either.

In this map you can identify isobars of 1008, 1012, and 1016.  There are no fronts to be observed in this image. There are no high pressure areas in this particular map either.  However, the 1008 isobar is surrounding a low pressure, directly south of Bangladesh.  All in all there does not seem to be much going on near Bangladesh.

In this map you can identify a large range of isobars, varying from 1008 to 1028.  There are also a few fronts in the northeast of Asia. There is one stationary front to the east of Bangladesh near a cyclone, and another stationary front to the north east of Bangladesh.  There is also a cold front to the northeast, but won’t be much concern to Bangladesh because it is heading southeast.

Global and Local Winds in Bangladesh

          There are multiple ways the location of Bangladesh affects the winds it receives.  Bangladesh is located 24°N and 90°E in the northern hemisphere.  This is located within the Hadley Cell in the three-cell atmospheric model, near the top by the horse latitudes where trade winds originate.  One of the global winds impacting Bangladesh is the north-easterly trade winds, which are coming from the north-east and blowing towards the south-west.  Bangladesh is also impacted by the subtropical jet stream located at 25°N, which tends to be weaker in the summer.  The location of Bangladesh is also near the subtropical high pressure belt.  So there are multiple global winds that have an effect on Bangladesh.
          The country of Bangladesh’s location plays a major role in determining what the weather and climate will be like.  In general, I think Bangladesh would have a fairly windy climate, considering there are so many types of global and local winds affecting the country.  One of the major winds that would affect the climate is the trade winds, which are consistently blowing south-west (see Global Wind Map below).

Also, because it is located between the subtropical high pressure belt, and the equatorial low, there should be a windy climate where the winds are travelling north to south.  This also, causes the air to converge at the subtropical pressure belt (horse latitudes), decrease in altitude, and then diverge out. (see Pressure Patterns Map below).

However, the subtropical jet stream could affect the weather conditions. This jet stream tends to be weaker in the summer, roughly around the El Nino season where the trade winds weaken as well. Sense the cause the north to south winds to weaken, the sea breeze is given an opportunity to bring moist clouds over the country of Bangladesh, and cause a lot of rain. This change in wind patterns in Bangladesh is referred to as a monsoon season.  The monsoon season is what prevents the country from having a dessert climate like many other countries around it, which have dessert climates due to being near the subtropical high pressure belt and the Coriolis Effect.  
          There are also some local winds that can affect Bangladesh.  There are no mountains in the country of Bangladesh.  Of the five winds and breezes that are associated with mountains -which includes mountain breeze, valley breeze, Chinook Winds, Katabatic Winds, and Foehn Winds- none of them have an effect on the weather in Bangladesh.  This is because Bangladesh is not located in the mountains or in a valley.  Local winds associated with coastlines have an impact on Bangladesh.  Bangladesh is located on the coastline of the Bay of Bengal in the Indian Ocean.  The 2 breezes associated with coastlines are sea breeze and land breeze, and both have an impact on Bangladesh.

Typical Weather and Tourism in Bangladesh

    The weather in Bangladesh is surprisingly warm during the Winter. For the month of December, the average maximum temperature is 32*C (79*F), and the average minimum temperature is 26*C (57*F). The Winter Solstice in Bangladesh occurs on December 22nd. Most likely there would be no precipitation on the Winter Solstice. The average rainfall in the month of December is 5mm (0 in.), which means there is a 3% chance that it will rain that month at all, and if it does it will only be on one day out of the whole month.

   Summer in Bangladesh is fairly warm, but not unbearable. For the month of June, the average maximum temperature is 32*C (89.6*F), and the average minimum temperature is 26*C (78.8*F). In Bangladesh the Summer Solstice  occurs on June 21st. The chances of there being rain on the Summer Solstice is very high. The average rainfall in the month of June is 315mm (12in.). There is a 70% chance of rain for the whole month, and on average it will rain 21 days just in the month of June alone.

    Spring seems to be more pleasant than Summer in Bangladesh. The month of March has an average maximum temperature of 32*C (90*F), and an average minimum temperature of 20*C (68*F). Bangladesh's Spring Equinox occurs on March 20th. There is a chance of rain on the Spring Equinox, but it is small. The average rainfall in the month of March is 61mm (2in.). On average it rains 5 days in the month of March, which means a 16% chance.

    Summer and Autumn in Bangladesh are almost identical in weather. The month of September has an average maximum temperature of 31*C (88*F), and an average minimum temperature of 26*C (79*F). The Autumnal Equinox in Bangladesh occurs on September 23. Like the Summer Solstice, the chances of there being rain on the Autumnal Equinox is very high. The average rainfall in the month of September is 248mm (10in.). There is a 63% chance of rain for the whole month, and on average it will rain 19 days in the month of September.

    The best time of year for tourists to visit Bangladesh is in the Winter. There are no potential weather hazards during the winter season. The average temperature is a nice cool 20*C (68*F). Another plus during the Winter is that there is almost no rain or wind. There are all kinds of activities for a tourist to do during this time of the year. Tourists can go to the beach sense the beaches will be calmer due to no wind or rain. They can also do hiking to see beautiful waterfalls and streams that are still flowing after the monsoon season.

Happiness comes when you go with the flow, so come float along our rivers and join us in our joy.

Here are just a few of the wonderful scenic spots in Bangladesh:

Here are some videos about visiting Bangladesh that make the country seem irresistible.
https://www.youtube.com/watch?v=OpVtkC8XCY4
https://www.youtube.com/watch?v=SJgMZE5G9yA

Temperature Controls in the city of Dhaka in Bangladesh

     The capitol city of Bangladesh is Dhaka. The latitude and longitude of Dhaka is 23.7° N, 90.3750° E. The warmest month of the year in Dhaka id May, with a mean temperature of 29°C (84.2°F), and the coldest month of the year in Dhaka is December, with a mean temperature of 20°C (68°F). The annual range of temperature in Bangladesh is 9°C (48.2°F). This information was found at:
http://www.dhaka.climatemps.com/temperatures.php
     A temperature control that has an impact on the city of Dhaka is ocean currents. Warm water is being blown by the wind up towards the poles. The wind then travels from the ocean, in this case the Indian Ocean, northward up from the coast of Bangladesh, and towards Dhaka. This contributes to the low range of temperature in Dhaka.
See map below: (Bangladesh is highlighted in red and yellow)

This map is from: http://www.vagaries.in/2012_08_01_archive.html

     Altitude is not a temperature control in Dhaka, or for most of Bangladesh, because the altitude for the whole country remains relative the same, and close to sea level. See map below:

This map if from: http://www.maps.com/map.aspx?pid=2123

It is predicted that within the next fifteen years the annual average temperature will go up about 4°C. While this may not seem like much, that small change could actually cause many problems for the city of Dhaka, and the country of Bangladesh. A ride in the average temperature causes sea levels to rise. If the sea level were to rise a few feet, the city of Dhaka, which is already a common flood zone, would suffer from more flooding. This could also possibly cause even more hurricanes with the warming water. Bangladesh already suffers from many natural disasters (flooding, hurricanes, tornadoes), and it seems will endure even more in the future. To read more visit:  http://www.preventionweb.net/files/574_10370.pdf or http://thecityfix.com/blog/pitfalls-potential-climate-change-vulnerability-dhaka-bangladesh-john-sinden/