11 July 2011
Posted in WFTV Severe Weather Center 9
El Nino and La Nina are the two most powerful weather phenomena on the planet and are known to alter the climate across more than half the planet! El Nino is the warming of water in the Pacific Ocean, determined by a comparison of average water temperatures over several years. If the ocean between the coasts of South America-Peru, Ecuador, Columbia-and the middle of the ocean toward the Date Line is warmer by 2-10 degrees F, we know that an El Nino is here. La Nina, officially called ENSO, is the cooling of water in the Pacific Ocean. El Nino and La Nina may alternate between every other year and every three years, so that the time from one El Nino to the next tends to be every three to seven years.
The tremendous phenomena of El Nino, known for its warming effect on the water in the Pacific Ocean is likely caused by underwater volcanic activity. El Nino weather can include rain and flooding along the Pacific coast, tornadoes and thunderstorms in the southern U.S., and fewer than normal hurricanes in the Atlantic. The warm waters of El Nino are also known to disrupt the food chain of fish, birds and sea mammals. During an El Nino, an increased dryness can occur in areas typically saturated with rainfall between November and March in the western Pacific over Indonesia and northern Australia. On the flip side, other areas such as Peru and Ecuador see an increase in rainfall. In fact, the El Nino was discovered in Peru by fishermen who noticed that every three to seven years, there was an increase in rainfall.
Satellite Image of El Nino
La Nina happens about half as often as El Nino. During a La Nina, winter temperatures in the U.S. are warmer than normal in the Southeast and cooler than normal in the Northwest. La Nina, known for its cooling effect on the water in the Pacific Ocean, can include weather like snow and rain on the west coast, unusually cold weather in Alaska, unusually warm weather in the rest of the U.S., drought in the southwest, and a higher than normal number of hurricanes in the Atlantic.
Satellite Image of La Nina
The reason there are fewer hurricanes during El Nino, despite warmer waters, can be explained by the jet stream, or a long, narrow, wandering current of high speed winds blowing from a generally westerly direction several miles above the Earth’s surface. El Nino tends to suppress the formation of hurricanes by steering the subtropical jet stream into the hurricane’s path and effectively cutting off the tops of the hurricanes with its strong winds, preventing them from growing any bigger. During a La Nina, on the other hand, the jet stream works in the advantage of a forming hurricane, allowing them to grow with ease and great intensity.