Tropical cyclone is a general term for all circulating weather systems with sustained winds over tropical waters. Tropical cyclones form only over warm water that is between five and twenty degress latitude. In order for a tropical cyclone to form, there must be a light wind, and the humidity must be high. First, an area of low pressure called a disturbance develops thunderstorms, that become organized and spiral inwards, forming the storm's center, called the "eye." The highest winds and the heaviest rain occur just outside the eye. There are three kinds of tropical storms: tropical depression, tropical storm, and hurricane (called a typhoon in the western Pacific Ocean, and a cyclone in the India Ocean).
A tropical depression is an organized system of clouds and thunderstorms that have a certain wind circulation, the wind speed must be sustained at thirty eight miles per hour or less. Tropical storms and hurricanes have a higher air pressure than a tropical depression, and tropical depressions also do not create a storm surge. A lot of heavy rain usually accompanies a tropical depression.
A tropical storm is a basically a hurricane, with less powerful winds. Like hurricanes, they have counter-clockwise winds, low pressure, and heavy rains. The only difference between a category 1 hurricane and the strongest tropical storm is one mile per hour. Tropical storms have winds of thirty nine to seventy three miles per hour, a category one hurricane has winds of seventy four miles per hour. There may be a little bit of storm surge flooding from a tropical storm in the area just to the right of where the center of the strom hits shore, the flooding will be even worse if the storm has a fast forward speed.
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Above is a table of the number of tropical storms per month that have formed between 1886 and 1997. September is the peak month for tropical storms to form, very few form in May and December.
Although tropical depressions aren't named, tropical storms and hurricanes are. Storms first started being officially named in 1953. In 1979, male names were added to the lists of names, up to that time, only female names were used. There are six lists of names, that we rotate through every six years. The first storm to form each year gets a name that starts with A, the second B, the third C, and so on through the alphabet. If a tropical storm or hurricane causes a lot of death or destruction, the name that it was given is taken off the lists and replaced with another.
This is a picture of tropical storm Isidor on September 26, 2002, courtesy of http://www1.ncdc.noaa.gov/pub/data/images/ts-isidore-20020926-0645- g82km.gif