Hurricanes

Guide Note

Hurricanes are powerful storm systems which form over the ocean and often move over portions of coastal land areas, which are then damaged by extraordinarily strong winds, heavy rain, and increased wave activity. The name hurricane is a common term for what is officially known as a tropical cyclone.

Hurricanes form out of thunderstorms, which pick up strength from the evaporation of warm, tropical waters, convergent wind patterns, and changing air pressure. A thunderstorm becomes a hurricane once wind speed is at or above 74 miles per hour.

A hurricane has a generally circular shape which swirls about a central area called the "eye" of the hurricane, inside of which it is relatively calm. Low pressure causes the violent storm to swirl around the eye, which can range in size from three to 230 miles in diameter.

Directly outside the eye is the "eyewall," the most violent portion of the entire hurricane where the highest wind speeds and greatest precipitation is found. Much of the damage caused by hurricanes comes from the turbulent eyewall passing over a region.

The outer fringes of the hurricane, while less powerful than the eyewall, are still powerful storms. These "rainbands" are regions of smaller thunderstorms that circulate about and feed into the central portion of the hurricane. While high winds and heavy rainfall happens within these bands, the areas between the bands are relatively calm.

Modern hurricanes are referred to by a person's name. These names are officially decided upon by either national weather offices or the World Meteorological Organization, and are given to the storms in order to decrease confusion when tracking multiple storms in a certain region.

Fast Facts

1. Notable hurricanes: Hurricane Katrina, Hurricane Andrew, the Galveston Hurricane of 1900.
2. Official Atlantic hurricane season lasts from from June 1 to November 30
3. Strong cyclones in the Northwest Pacific Ocean are called typhoons
4. Hurricane Classifications:
   • Category 1: 74-95 mph
   • Category 2: 96-110 mph
   • Category 3: 111-130 mph
   • Category 4: 131-155 mph
   • Category 5: 155+ mph