Tropical Storms and Hurricanes

Abstract

The tropical disturbances having wind speeds below 63 knots are known as depressions, cyclonic storms and severe cyclonic storms. More intense cyclonic storms with winds over 63 knots around a low pressure center spirally form over the tropical oceans at latitudes between 7° and 15°. Such systems are known as cyclones in India, hurricanes in North America and the Caribbean area, and typhoons in Japan. After their formation they start moving at a speed of around 15 km per hour generally to the west over the open waters of the oceans. The tropical cyclones produce heavy clouds, rough seas and very heavy rainfall. A well-developed hurricane is a hazard to ships in its proximity as well as to the coastal area where it strikes. The storm piles up a huge sheet of sea water in its forward sector which can inundate low lying coastal areas causing large scale death and destruction. This is known as storm surge, which can be 80 km wide and four meters deep and is the most devastating feature associated with a hurricane. Nine out of ten hurricane fatalities are caused by storm surges. For example, the infamous tropical cyclone, which struck Bangladesh in November 1970, was responsible for killing nearly 300,000 people as a result of storm surge, while hurricane Mitch that struck central America in October, 1998, caused fatalities in excess of 11000 and the total damage was worth millions of U.S. dollars.