El Nino and La Nina
El Nino and La Nina are important temperature changes to the Pacific Ocean surface water. El Nino means “the boy”, while La Nina means “the girl” in Spanish.
In many ways, the two events are polar opposites. El Nino is the result of warmer conditions in the eastern portion of the Pacific Ocean (read about the causes of El Nino), while La Nina comes from the cooling of these same waters, accompanied by the strengthening of the east-west trade winds.
El Nino and La Nina also occur with different frequencies. La Nina usually occurs half as often as El Nino which happens every three to six years.
Both El Nino and La Nina have big impacts on North America. However, these two events bring very different weather conditions to the same areas.
For example, during an El Nino event, winters in North America are warmer and drier in the Northwest, Upper Central Plains and Northeast, resulting in less snow. However, La Nina will affect the Midwest, Northern Rockies, Northern California and the Pacific Northwest with precipitation levels that are much above normal.
Meanwhile, the Southwest portion of the United States along with northern Mexico will see a cooler and wetter winter season with El Nino, while these same regions would be drier than normal with La Nina.
While El Nino can bring floods to areas in South America, like the coast of Peru and Ecuador, La Nina will bring in droughts to these areas. La Nina also causes Brazil to be much wetter than normal from December through February. With El Nino, Canada will experience a warmer and drier winter while La Nina will lead to a cooler, snowier winter season in Canada.
The two events can affect the hurricane seasons. While El Nino reduces the number of hurricanes, thanks to a shift in the position of the Atlantic high pressure ridge, and creates stronger upper level wind shear, La Nina will do just the opposite. Read about the El Nino effects.
La Nina has the opposite effect on the Atlantic Basin hurricane season as compared to El Nino. With a La Nina event, the wind shear is decreased over both the Caribbean Sea and the Atlantic Ocean. As a result, towering thunderstorms have a chance to grow and climb into the upper levels of the atmosphere and can eventually grow into hurricanes if other conditions are present.
For example, a La Nina event developed in 2008 and helped create one of the most active hurricane seasons since 1944. In 2008, there were 16 named storms, eight of which became hurricanes.
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