La Niña

La Niña can be described as a more exaggerated version of a normal year. The La Niña effect occurs every 3-5 years when strong trade winds blowing from east to west decrease surface sea temperatures in the tropical eastern Pacific. Strong trade winds warm and moisten as they travel west over the Pacific. Warm, moist air rises in the western Pacific, forming low pressure. As the warm, moist air rises into the atmosphere, it cools and condenses, increasing precipitation.

La Nina

The dry air moves east through the upper atmosphere, cools and sinks in the eastern Pacific. This falling dry air forms an area of high pressure, leading to drought in the eastern Pacific.