This question is the subject of so many searches being done over the internet, I guess mostly by people affected by the occurrence of hurricanes.
 
Hurricanes always have their beginnings, and grow its strength, over warm ocean water. An ocean temperature of 80 degrees Fahrenheit is enough to cause large volumes of water to evaporate and make the air very humid. The water vapor rising in the hot humid air condenses into clouds, which becomes the source of rain water. As more hot air rises, wind is created.

Tropical cyclones is the generic name for storms, which include typhoons and hurricanes. It start as disorganized clusters of showers and thunderstorms. When its winds become organized, making a complete circle around a center, with sustained strength of less than 39 mph, it becomes a tropical depression. Once the wind strength breaches that mark, it develops into a storm and given a name. Finally, it turns into a hurricane when its sustained wind surpasses 74 mph.The rotation of the Earth causes the wind to follow a curved path, which gives hurricanes its circular form as seen in satellite images.


For hurricanes to form, the winds just above the ocean surface, up to an altitude of 40,000 feet, must be blowing in the same direction at the same speed. The presence of winds blowing in the opposite direction, in the same area and altitude, prevents the hurricane from growing. As it moves over cooler waters or land, cut off from warm, humid air, hurricanes eventually weaken and die.