A hurricane is a powerful tropical cyclone with sustained winds of at least 74 mph that often measures several hundred miles in diameter. All Atlantic and Gulf of Mexico coastal areas are subject to hurricanes and tropical storms. Parts of the Southwest United States and the Pacific Coast often experience heavy rains and floods from hurricanes spawned off Mexico. The Atlantic hurricane season lasts from June through November with the peak season from mid-August to late October.

Hurricanes can cause catastrophic damage to coastlines and several hundred miles inland. Sustained winds in the strongest hurricanes (Category 5 on the Saffir-Simpson Hurricane Wind Scale) can exceed 155 miles per hour with higher gusts. Hurricanes and tropical storms can also spawn tornadoes, create damaging storm surge inundation along the coast and cause extensive flood damage along the coast and inland from heavy rainfall.

Hurricanes Have Two Main Parts:

1. The eye of the hurricane is an area of nearly calm winds in the center of the storm where the lowest pressure resides. The eye of a hurricane averages about 20 miles in diameter and often has very few clouds.
   
   
2. The second part is the wall of very tall clouds that surrounds the relatively calm eye. This region, known as the eye wall, is where the hurricane's strongest winds and heaviest rain occur. 

How Hurricanes Form

There are several favorable environmental conditions that must be in place before a hurricane can form. They are:

• Warm ocean waters (at least 80°F / 26°C) throughout a depth of about 150 feet. (46 m).
  
  
• A pre-existing atmospheric disturbance such as a tropical wave or decaying frontal boundary.
  
  
• A moist  and unstable atmosphere that supports sustained shower and thunderstorm activity.
  
  
• Low values (generally less than about 23 mph / 37 kmph) of vertical wind shear between the ocean surface and the middle or upper atmosphere. Vertical wind shear is the change in wind speed and/or direction with height.

A hurricane goes through many stages as it develops:

1. Warm, moist air over the ocean rises and spirals into an organizing low air pressure area. This produces an increasing area of heavy rain and thunderstorms that is called a tropical disturbance.
   
   
2. As air pressure continues falling and  sustained winds increase, a tropical depression is classified by the National Hurricane Center.  Winds within a tropical depression are 38 mph or less.
   
   
3. When sustained winds reach 39mph, the tropical cyclone is classified a tropical storm by the National Hurricane Center (tropical cyclones are given names when they begin to have winds of this speed).
   
   
4. The tropical storm becomes a Category 1 hurricane when sustained winds reach 74 miles per hour.  The Saffir-Simpson Hurricane Wind Scale has five categories.  Major hurricanes are considered to be Category 3 strength or greater with sustained winds of 111 mph or higher.


When a Hurricane Strikes

When hurricanes move onto land, the heavy rain, strong winds, storm surge and  crashing waves can damage buildings, trees, cars, and other infrastructure. Winds pile up and push ocean and bay waters towards the coast which is known as the storm surge.  Water weighs approximately 1,700 pounds per cubic yard and the pounding of frequent waves can demolish structures not designed to withstand such forces. The combination of storm surge and the prevailing tide levels are called the storm tide.  The powerful and extremely dangerous force of storm tides and crashing waves is the major reason why you MUST stay away from coastal areas during a tropical storm or hurricane warning

Technical Information Provided by FEMA, the National Hurricane Center, and the National Weather Service.