El Niño is an abnormal warming of ocean waters in the eastern tropical Pacific that occurs irregularly every few years. Normally, trade winds blow warm water westward, making the eastern Pacific cooler. During El Niño, the trade winds weaken, allowing warm water to flow back east. This changes weather patterns globally, bringing heavy rain to normally dry regions like Peru while causing drought in places like Indonesia. El Niño's shifting ocean temperatures influence the formation of storms and pressure systems that affect temperatures and rainfall around the world.