Weather Perturbations Associated With The Transit Of Tropical Cyclones In The Coast Of Bangladesh

During the transition of tropical cyclone in the coast of Bangladesh, it is normally observed that there is a noticeable perturbation of weather parameters around the cyclone landfall zone. Through this research the extent of perturbation is assessed. To make the inventory 4 recent cyclones were selected that had made landfall in Bangladesh coast. They are cyclone MORA, cyclone ROANU, cyclone KOMEN and cyclone MAHASEN. Weather parameters selected to check their perturbation are wind speed, temperature, dew point temperature, atmospheric pressure, relative humidity and precipitation. The dispersion of these parameters from their normal state was measured also in accordance of their distance from the landfall area. To perform the task a time scale of 15 days was selected for each cyclone. Middle 3 days window were considered as most affected weather, 6 days prior and after the event were considered as normal (prevailing) weather. The Synop (observed) data was downloaded from the Ogimet.com. The data was then processed and decoded by Synop decoder and then further analyzed in MS Excel. In case of atmospheric pressure perturbation the highest perturbation was found 5.8 mb low on average than prevailing pressure up to 50 km from cyclone landfall. Wind speed perturbation was highest in 50 to 100 km area. Perturbation of temperature was highest in 0 to 50 km (about 2.1 °C low on average). Perturbation of dew point temperature was found negligible and humidity perturbation was found highest 6.63% high on average up to 50 km of landfall. In case of precipitation perturbation highest was found in 0 to 50 km area of landfall (38.76 mm high on average than prevailing weather), however precipitation perturbation was irregular beyond 100 km of landfall. The most perturbed weather parameter was found atmospheric pressure and the least affected was dew point temperature.