This series of six images shows the evolution of atmospheric water vapor over the Pacific Ocean during the 1998 El Nino condition. Higher than normal ocean water temperatures increase the rate of evaporation, and the resulting warm moist air rises into the atmosphere, altering global weather patterns. Data obtained by the Microwave Limb Sounder (MLS) on NASA's Upper Atmosphere Research Satellite (UARS) during January and February 1998 show a decrease in the extent of high levels of water vapor (red) over the eastern equatorial Pacific and an increase in water vapor (yellow to red) over the northwestern Pacific off the coast of Japan. This area is a breeding ground for winter storms that move eastward toward North America. During this El Nino condition, the southern tropical jet stream has shifted northward, bringing additional moisture from the tropics. When these two sources of moisture converge near California, they produce storms with higher-than-normal rainfall.