Reported September 2008

What's the Forecast?: Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Humankind has attempted to predict the weather since ancient times. For millennia, people have tried to forecast the weather. In 650 B.C., the Babylonians predicted the weather from cloud patterns. In about 340 B.C., Aristotle described weather patterns in Meteorologica. Chinese weather prediction lore extends at least as far back as 300 B.C.. Ancient weather forecasting methods usually relied on observed patterns of events. For example, it might be observed that if the sunset was particularly red, the following day would bring fair weather. This experience accumulated over the generations to produce weather lore. Today, weather forecasts are made by collecting data about the current state of the atmosphere and using computer models of the atmospheric processes to project how the atmosphere will evolve.

About Hurricanes: A hurricane is a type of tropical cyclone, a low-pressure system that usually forms in the tropics and has winds that circulate counterclockwise near the earth's surface. Storms are considered hurricanes when their wind speeds surpass 74 MPH. Every hurricane arises from the combination of warm water and moist warm air. Tropical thunderstorms drift out over warm ocean waters and encounter winds coming in from near the equator. Warm, moist air from the ocean surface rises rapidly, encounters cooler air, and condenses into water vapor to form storm clouds -- releasing heat in the process. This heat causes the condensation process to continue so more and more warm moist air is drawn into the developing storm. This creates a wind pattern that spirals around the relatively calm center, or eye, of the storm, much like water swirling down a drain. The winds keep circling and accelerating to form a classic cyclone pattern.

The American Geophysical Union and the American Meteorological Society contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

John Bluck
Public Affairs
NASA Ames Research Center
(650) 604-5026
John.G.Bluck@nas.gov

American Geophysical Union
(800) 966-2481
http://www.agu.org

American Meteorological Society
Boston, MA 02108-3693
(617) 227-2425
http://www.ametsoc.org