El Niño Update

Intense warming of the ocean waters across the Eastern and Central Tropical Pacific Ocean, due to the phenomenon known as the El Niño/Southern Oscillation (ENSO), has developed since March 1997. The El Niño developed very rapidly during April-May, and reached high intensity by June. This event is comparable in magnitude and extent to the 1982/83 episode, which was one of the strongest El Niño of the century. Prediction products from several prediction centres around the world indicate these conditions will probably persist during the northern hemispheric spring season of 1998. Based on past warm episodes and on current long-range forecasts, the El Niño is expected to weaken during the late spring and early summer of 1998. Features accompanying the current El Niño include: abnormal patterns of rainfall and cloudiness over most of the global tropics, a nearly complete shut-down of the normal easterly winds across the entire tropical Pacific and abnormal air pressure patterns throughout the global tropics. Thus far, the primary El Niño impacts have been in the tropics and subtropics, and across the eastern South Pacific and Central South America. These has also been a dramatic decrease in tropical storm and hurricane activity across the subtropical North Atlantic and an expanded area of favorable conditions for tropical cyclone activity over the eastern North Pacific. It is summary of: (i) our knowledge of the El Niño phenomenon, (ii) its associated impacts on a global scale, and (iii) forecast information for the coming months. This Update is compiled from a variety of scientific sources including several major global climate prediction centres, and is intended to address the questions and concerns of an audience that ranges from the general public to the policy maker. The background information (part 1 of the Update) is covered in somewhat greater detail in this issue. Future updated will focus primarily on climate monitoring and forecast information (part 2 of this Update) which will be updated each month