Facts About Cyclones

Formation

• Cyclones do not form spontaneously; the atmospheric conditions and water temperatures must be just right in the tropical oceanic regions. The water temperatures must be at least 80 degrees Fahrenheit to a depth of about 150 feet. The moist atmosphere also needs to cool fast enough as it goes up to produce the thunderstorm activity that allows the heat from the ocean waters to be used for the development of the cyclone. According to the Atlantic Oceanographic and Meteorological Laboratory (AOML), several weak but still-forming thunderstorms must come together with enough circular motion to create spin.

Regions

• Cyclones go by different names, depending on the region. The rotation of the winds also depends on the region. A cyclone rotates counter-clockwise in the northern hemisphere and clockwise southern hemisphere. Cyclones are called hurricanes in the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline and the South Pacific Ocean east of 160 degrees East. They are referred to as typhoons in the Northwest Pacific Ocean west of the dateline. They are "severe tropical cyclones" or "Category 3 (and above) cyclones" in the Southwest Pacific Ocean west of 160 degrees East and the Southeast Indian Ocean east of 90 degrees East. Cyclones are also called "very severe cyclonic storms" in the North Indian Ocean and "tropical cyclones" in the Southwest Indian Ocean. According to the AOML, a cyclone or cyclonic-type storm may develop in the Mediterranean Sea, but this is rare.

Categories

• Cyclones are separated into categories based on their wind strength. Category 1 is the weakest, with winds of up to 77 miles per hour. Category 5 is the strongest, with winds above 174 miles per hour. A Category 1 storm produces some damage to trees and farmland. For a Category 1 storm, weather officials recommend securing all outdoor furniture and equipment to minimize damage. Safety officials usually call for a mandatory evacuation of an area if a Category 5 cyclone is predicted. Category 5 storms cause widespread damage, power failures and airborne debris, which is one of the most dangerous hazards.

The Eye of the Storm

• The "eye" of the storm is generally a calm, cloudless, circular area with little to no rain and fairly light winds, whereas winds around the eye can reach speeds of up to 125 miles per hour. The eye can vary in size, from roughly 6 miles to more than 60 miles across, depending on the severity of the cyclone. Tropical Cyclone Yasi, which hit Queensland, Australia in 2011, was a Category 5 cyclone with an eye that was 10 nautical miles wide.