The hurricane works like a simple steam machine, with hot and humid air providing its fuel.

When the sun ray heat the ocean waters, the humid air heats, expands and begins to elevate like a hot air balloon. More humid air replaces that air and the process is started again.

Certain elements need to be present so a hurricane can be formed:
 

HOW LARGE IS A HURRICANE?

A hurricane is usually 8 to 10 kilometers high and 500 to 100 km wide, but its size mat vary considerably.

The smallest hurricanes can have a diameter of only 40 km, while in the largest it can be from 600 to 800 km. The most gigantic hurricanes are formed at the Pacific Ocean and can have a diameter of up to 1,700 km.

The eye of the hurricane is usually 25 to 35 km, although it may vary considerably. The eye of Pacific hurricanes, where the cyclones have more water to travel before reaching land, tends to be the largest in the world, with an approximate diameter of 80 km.

WHERE ARE HURRICANES ORIGINATED?

 Since sea temperatures must be over 80 F, hurricanes are going to be originated in different places during different months of the year, usually during the hottest season. Hurricanes take place at every tropical area except the Southern Atlantic and Southern Pacific.

Remember that the hurricane needs plenty of ocean to gain strength and nourish, and moves with the earth’s rotation towards the west. This implies that it will be formed when it can travel with no interruptions or weakened by land. There are tropical waves forming all the time, but not all of them have the conditions and space to gain strength.
 
STRUCTURE OF THE HURRICANE

This steam machine has a center that is warmer than the air surrounding it. It receives its energy from condensation from the water steam.

The steam (originated by sea evaporation) begins to expand and ascend quickly. When reaching the highest areas of the atmospheres where the temperature is not so high, steam condensates again, releasing a large amount of energy and originating huge clouds (which may reach heights of 15,000 m) and abundant rain. This phenomenon is clearly perceived in satellite images shown in the weather forecast on TV.

At the lower portion of the hurricanes (up to 3,000 m) the air is sucked towards its center. At the middle levels, an ascending cyclonic circulation is present (spinning around the center). And at the top of the hurricane, above up to 6,000 m, the air moves outwards.
 
THE FAMOUS EYE OF THE HURRICANE

 The eye is an area of relative calm at the center of a hurricane, which extends from the sea level to the top and is surrounded by a wall of thick rain-laden clouds. When reaching the high areas of the atmosphere, where the temperature is not so high, and these steam condensates again, releasing a large amount of energy and originating hug clouds (which may reach heights of 15,000 m) and abundant rain. This is what is most interesting when observing the hurricane from a satellite.

The larger the hurricane is, the more clearly the eye can be seen, except if very high clouds prevent the view.

The wall of the eye is an area where two opposing forces can be found: The force of the air moving towards the center and the centrifugal force that goes outwards. The most intense winds are at the wall of the eye and the tornadoes are originated there.

The presence of the eye and the wall tell a hurricane apart from a tropical storm (which has no eyes and whose winds are slower).

The size of the eye is not always proportional to the magnitude of the hurricane, although the largest have been seen in the 4 category.
 
HURRIANE SEASON

There is a general pattern which is more or less constant, but may vary according to the weather conditions.

In the Atlantic, Caribbean and Mexican Gulf the season begins on July 1st, due to the water heating during the summer, and extends until November 30th, although hurricanes may take place year round (except March). At the Mexican Gulf and Occidental Caribbean, being more calm waters, the heating precedes the rest, originating the first cyclonic systems of the season.

As the summer Sun advances, or the sun shifts to more boreal latitudes (towards the North) as the hurricanes are produced to the North of the Caribbean and travel, according to the earth’s rotation, towards the West, frequently arriving at the East Coast of the United States after passing through Caribbean countries, especially Puerto Rico, Cuba, Bahamas, etc. Firs they arrive to the coast of Florida and, as the summer advances (August – September) and according to the strength of the hurricane, may arrive to the central states of the US and even to the Northern states of the Atlantic coast and move inland.  At the end of the season, when the water cools again, hurricanes form at the Caribbean and the Gulf again.

At the Pacific Ocean, as a result of the cold currents of the Humboldt, the temperature of the water rarely exceeds 80°F, rarely forming a hurricane. The “El Niño Current”, which increases the ocean temperature, can be the exception. The West movement (by earth’s rotation, as mentioned before) of the hurricanes further decreases the probabilities of one arriving to the coasts of Chile, Peru or Ecuador. Much more likely, as mentioned at the beginning, it that they originate further North and moving towards Asia affecting Japan, Hong Kong, Philippines, etc.

Hurricanes are classified in five categories based on wind speed, central pressure and potential damage. Category three and beyond are considered the most serious hurricanes, although categories one and two are still extremely dangerous and require your full attention.

How are Hurricane Categories Determined?

Hurricanes can produce generalized torrential rains. Floods cause deaths and are quite destructive. Slow storms and tropical storms moving toward mountain areas are prone to produce mostly strong rainfall. Excess rainfall can cause mudslides or landslides, especially in mountain areas. Flash floods can occur as a result of intense rainfall. Flooding in rivers and creeks may persist for several days or more after the storm.

Between 1970 and 1999, more people have lost their lives due to freshwater floods associated with tropical cyclones than any other type of risk related to tropical cyclones.

How are names assigned to Hurricanes?

Since 1953, tropical storms from the Atlantic Ocean have been assigned a name from lists generated by the National Hurricane Center and now kept and updated by an international committee of the World Meteorological Organization. Only female names are in the list up to 1979. Afterward, male and female names are alternated. Six lists are used in the rotation. Therefore, the 2001 lists will be used again in 2007.

The list is only changed when a storm is so fatal or costly that the continual use of the name would be inappropriate due to sensitive reasons. In this case, the name is withdrawn from the list and a different name is selected to replace it.