What is a hurricane?

• A hurricane is a type of tropical cyclone (the general term for all circulating weather systems which form over tropical waters.)

Tropical cyclones are classified as follows:

• Tropical Storm: An organized system of strong thunderstorms with a defined circulation and maximum sustained winds of 39 to 73 mph (34-63 knots).
• Hurricane: An intense tropical weather system with a well defined circulation and maximum sustained winds of 74 mph (64 knots) or higher. In the western Pacific, hurricanes are called "typhoons," and similar storms in the Indian Ocean are called "cyclones."
• Tropical cyclones are classified according to the Saffir-Simpson Scale.
• Category 1 (Minimal Damage):
  Pressure > 28.94 "Hg, Winds 74-95 mph, Storm surge 4-5'
• Category 2 (Moderate Damage):
  Pressure 28.50-28.91 "Hg, Winds 96-110 mph, Storm surge 6-8'
• Category 3 (Extensive Damage):
  Pressure 27.91-28.47 "Hg, Winds 111-130 mph, Storm surge 9-12'
• Category 4 (Extreme Damage):
  Pressure 27.17-27.88 "Hg, Winds 131-155 mph, Storm surge 13-18'
• Category 5 (Catastrophic Damage):
  Pressure < 27.17 "Hg, Winds > 155 mph, Storm surge > 18'

How do hurricanes form?

• Hurricanes are products of the tropical ocean and atmosphere. They are powered by heat from the sea, and they are steered by the easterly trade winds and the temperate westerlies as well as by their own energy. Around their core, winds grow with great velocity, generating violent seas.
• Developing hurricanes gather heat and energy through contact with warm ocean waters. The addition of moisture by evaporation from the sea surface powers them like giant heat engines
• Moving ashore, they sweep the ocean inward while spawning tornadoes and producing torrential rains and floods.

Where and when do hurricanes usually form?

• In the eastern Pacific, hurricanes begin forming by mid-May
• In the Atlantic, Caribbean, and Gulf of Mexico, hurricane development starts in June.
• For the United States, the peak hurricane threat exists from mid-August to late October although the official hurricane season extends through November.
• Over other parts of the world, such as the western Pacific, hurricanes can occur year-round.
• Each year on average, ten tropical storms (of which six become hurricanes) develop over the Atlantic Ocean, Caribbean Sea, or Gulf of Mexico. Many of these remain over the ocean. However, about five hurricanes strike the United States coastline every 3 years. Of these five, two will be major hurricanes (category 3 or greater on the Saffir-Simpson Hurricane Scale).

What are some of the hazards associated with hurricanes?

• Storm Surge
  
  Storm surge is a large dome of water often 50 to 100 miles wide that sweeps across the coastline near where a hurricane makes landfall. The surge of high water topped by waves is devastating. The stronger the hurricane and the shallower the offshore water, the higher the surge will be. Along the immediate coast, storm surge is the greatest threat to life and property.
• Storm Tide
  
  The storm tide is the combination of the storm surge and the normal astronomical tide. If the storm surge arrives at the same time as the high tide, the water height will be even greater.
• Winds
  
  Hurricane-force winds, 74 mph or more, can destroy poorly constructed buildings and mobile homes. Debris, such as signs, roofing material, siding, and small items left outside, become flying missiles in hurricanes. Winds often stay above hurricane strength well inland.
• Heavy Rains/Floods
  
  Widespread torrential rains often in excess of 6 inches can produce deadly and destructive floods. This is the major threat to areas well inland.
• Tornadoes
  
  Hurricanes also produce tornadoes, which add to the hurricane's destructive power. These tornadoes most often occur in thunderstorms embedded in rain bands well away from the center of the hurricane. However, they can also occur near the eyewall.

What areas are most likely to be hit by a Hurricane?

• All Atlantic and Gulf coastal areas are subject to hurricanes or tropical storms. Although rarely directly struck by hurricanes, parts of the Southwest United States and Pacific Coast suffer heavy rain and floods each year from the remnants of hurricanes spawned off Mexico.
• Islands, such as Hawaii, Guam, American Samoa, and Puerto Rico, are also subject to hurricanes. Due to the limited number of evacuation routes, barrier islands are especially vulnerable to hurricanes.

Where can I find out more about Hurricanes?

• Hurricane Net
• Hurricanes, Unleashing Nature's Fury - pdf file
• Tropical Prediction Center
• Hurricane Watch Office/ Office of Meteorology