According to NASA, approximately 85 hurricanes occur worldwide each year. Not all of these hurricanes are devastating; some of them appear to be ordinary storms for the most part and only develop into official hurricanes for a few short hours, whereas others can be considered full-force hurricanes for several weeks. In order to be considered an official hurricane, in addition to having an eye with low atmospheric pressure, the circulating wind speeds should exceed 74 miles per hour.
Hurricanes most often start in tropical areas near the Tropic of Capricorn or Tropic of Cancer. Wind and air movements in the regions north or south of the tropics help to produce the spinning effects of the hurricanes that are formed. Because of this, it is actually rare for a hurricane to form close to the equator. Hurricanes do not travel over land, and therefore dissipate shortly after reaching a shore. However, the effects of a hurricane, such as storms, rain, wind and other adverse weather patterns can be evident farther into land masses.
A hurricane also cannot develop over bodies of water where the surface of the sea is lower than 26.5 degrees Fahrenheit. Although scientists are able to estimate how many hurricanes occur each year and when a potential hurricane may occur and approach a shoreline, it can be difficult to predict how intense a hurricane might be.