Tropical Cyclones
Tropical cyclones are rotating masses of air containing clouds, wind and thunderstorms that funnel energy from the (warm) surface of the ocean to the (cooler) atmosphere above. Warm moisture-laden air rises from the surface of the ocean and condenses to form clouds higher up in the atmosphere. The upward motion of air creates a low pressure system that sucks in more air from its surroundings.
Under the right conditions-warm oceans, plentiful moisture and a lack of winds to disturb the upward flow of air-cyclones can become self-perpetuating, sucking in surrounding air ever more voraciously. When sustained wind speeds of 60-120 kilometers per hour are reached, cyclones acquire their trademark spiral shape, and are assigned a name by America’s National Weather Service. At the storm’s eye, where atmospheric pressure is the lowest, things stay relatively calm. But areas under the surrounding eyewall are lashed with the most powerful winds and thunderstorms.
Facts & Numbers:
Last month, climatologists at Louisiana State University examined hurricane records dating back to 1851. These are some of their findings:
Greatest number of named storms in a season: 21, in 1933
Second-greatest number of named storms: 19, in 1887 and 1995
Average number of named storms per season: 9.6
Top 10 seasons with the earliest occurrences of named storms: 1887, 1893, 1933, 1936, 1990, 1995, 1996, 2003, 2004 and 2005.
Average number of named storms during such “early start” seasons: 16.1
Projected number of named storms in 2005: 18-21
Projected number of hurricanes in 2005: 9-11
Projected number of intense hurricanes in 2005: 5-7
Sources: National Oceanic and Atmospheric Administration (NOAA), Louisiana State University
