Ordinarily, during normal conditions, the southeast trade winds blow so intensely that they build up to cause a sea level difference of up to 40cm greater on the western side of the Pacific Ocean, resulting in an increased amount of warm water (between 28oC to 30oC) along Australia and the other western continents. This warm water along the western edge of the Pacific then creates a low pressure zone, promoting heavier rainfalls, where as along the eastern edge of the Pacific, the cooler water creates a high pressure zone which results in more stable conditions with less rain.

A normal year view, as it would look from the equator.(Taken from www.carleton.ca)