El Ni�o is believed to be primarily responsible for the California storms. The term "El Ni�o" has evolved to refer to the anomalous warming of the eastern equatorial Pacific Ocean that occurs every few years. Lately, the span in time between El Ni�o occurrences has been between 2 and 5 years.

The current El Ni�o or warm episode began during the first quarter of 1997 and had signs that it was going to start during the last quarter of 1996. Warm episodes typically persist anywhere from 15 months to two-years. The forecasts for the 1997-1998 warm episode show El Ni�o gradually waning during the summer of 1998 with sea surface temperatures in offshore Ecuador and Peru returning to near normal or slightly cooler than normal by late summer or early fall. This indicates that the effect of El Ni�o on the development of tropical disturbances in the North Atlantic basin will be waning near the peak of the hurricane season. This peak occurs between August 15th and September 15th each summer.

The present El Ni�o favors the possibility of hybrid storms forming in the Gulf of Mexico, near the Bahamas or off the southeast coast of the United States late in spring or early in summer. Hybrid storms are low pressure systems that have a mixture of tropical and non-tropical characteristics and can't be truly classified as being purely either one. These storms tend to occur mostly during the warmer portion of the transition seasons, late spring and early fall, when the sea surface temperatures are still quite warm, but cooler temperatures at the surface and aloft are not too far away and typically somewhat more vigorous than during the summer.

The areas that are expected to be favorites for the generation of tropical disturbances that eventually become tropical storms and hurricanes include the tropical North Atlantic, mostly north of 13 North latitude, the northwest Caribbean Sea, and the western Gulf of Mexico region. The former two are expected to be more active this season than the latter one. This premise is based on the tendency of upper air pressure troughs to form in or move into the U. S. East Coast region. Thus, tropical storm systems are likely to follow a path that curves northwest to northward around the southern and western portions of the high pressure system that usually dominates the North Atlantic Ocean’s subtropical latitudes each summer.

Overall, the waning effects of El Ni�o are likely to allow a few more named storms to form this year than occurred last year. Between 7 and 10 named storms are expected during the course of the 1998 hurricane season.