Trade winds are weak, and upwelling off Ecuador and Peru ceases. This causes drought in Indonesia, storms in Tahiti, and ultimately the Peru Current is weakened and fishing is poor. When El Ni o occurs, the trade winds become weak and stop moving the warm water away from the coast. The warm water in the middle of the Pacific causes the winds to blow toward the warm pool. Clouds form over the new warm pool, fed by the moist winds collected from all around it, to the west and to the east.
Heavy rains are the result, while New Guinea to the west is now rather dry.
The warm pool extends eastward as the trade winds weaken, and now moist winds can enter land, where they rise up toward the mountains, making clouds and causing heavy rains. Peru and Ecuador are not the only places affected. In the north Pacific, the California Current loses strength because of weakening of the offshore high pressure region and expansion of the Aleutian Low. Warm water then moves northward along the coast, only weakly opposed by the California Current. Warm moist air invades southern California and also Arizona causing large amounts of rainfall.