What Is A Tropical Storm?
A tropical storm is essentially a very intense thunderstorm which involves extremely low pressure and cyclonic wind rotation. Sometimes, tropical storms are referred to as tropical cyclones, but this term also embraces other weather systems such as tropical depressions; typhoons and hurricanes. A tropical storm requires a sustained wind speed of 39 miles per hour – if this increases to 74 miles per hour it is classified as a hurricane. So much for definitions, but just how do tropical storms start? Well, as you'll see, a number of conditions all have to be met before nature can unleash its destructive power.
The warm waters over which the tropical storm forms generate a lot of warm moist air (through the process of evaporation of the surface waters). The heat in the system causes the moisture laden air to rise. As it does so, a low pressure zone (depression) is created, which causes surrounding air to flow in to balance the pressure difference, generating a spinning weather system. As the warm air rises into the atmosphere, it cools and the moisture condenses out, forming clouds.
For a tropical storm to form, there need to be surface level winds blowing from various directions which converge and assist the process of warm, moist air rising. An additional condition is that there should be little wind shear at higher altitudes as this allows the storm clouds to rise vertically to high levels. A tropical storm system may be six miles in height and up to 400 miles across. The storm will cause very large waves if the storm remains at sea, but its full destructive force is unleashed when the very strong winds, waves and torrential rain associated with the storm encounter land and human habitations.
In a tropical cyclone, as little as 3% of the heat energy, contained in the rising moist air, may be converted into mechanical energy of the circulating winds. This relatively small amount of mechanical energy equates to a power supply of 1.5x1012 Watts - equivalent to about half the world-wide electrical generating capacity. No wonder tropical storms and hurricanes can be so destructive!