by Sarah Dillingham
The Climate Prediction Center released its latest El Nino/Southern Oscillation (ENSO) forecast last week stating that an El Nino Watch remains in place as conditions are favorable for El Nino development within the next 6 months. The presence of an El Nino or La Nina episode is determined by analyzing the water temperatures in the eastern equatorial Pacific Ocean and comparing those to water temperatures typically seen in that region. Warmer than average water temperatures indicate El Nino conditions, and cooler than average water temperatures indicate La Nina conditions. Right now, the Climate Prediction Center says neutral conditions have persisted through the month of August, but El Nino is still forecast to began as early as late September to early October.
El Nino and La Nina events can have a variety of impacts on local climates, and the U.S. is certainly no stranger to that after having 2 consecutive La Nina episodes that have brought severe drought conditions to the South and Midwest. The first of these episodes began when the Pacific waters cooled during the summer of 2010, resulting in a moderate to strong La Nina which lasted through late May 2011. Resulting weather patterns from this La Nina led to the onset of the first round of severe drought in the Southern Plains. Over the summer of 2011, conditions became near-neutral before again returning to La Nina conditions in early fall of 2011. The more recent La Nina continued through spring of 2012, and allowed drought conditions to persist across portions of the Southern Plains and the West, while aiding in the development of severe drought now in place across the Midwest.
As we prepare to shift into El Nino conditions, areas of western Canada, Alaska, and northern areas of the contiguous U.S. can expect to see warmer than normal conditions as warm air is allowed to push farther north. Residents of the Southeast can expect to see a cooler and wetter pattern develop as more intense storm systems move through the Gulf of Mexico.
Another important impact of ENSO events is that the development of El Nino typically suppresses tropical cyclone development. You may recall that early forecasts for the 2012 Atlantic Hurricane Season reflected a slightly below normal to near normal season, due to the possibility of a developing El Nino. However, this year’s belabored arrival of El Nino combined with very warm Atlantic Ocean temperatures, caused NOAA and the National Hurricane Center to increase their tropical cyclone numbers for the 2012 season in their August 9 update. While El Nino is typically bad for tropical cyclone development, it will not always mean we see a slow season as the summer and fall of 2004 experienced a weak El Nino event, when 15 named storms formed in the Atlantic.
The Climate Prediction Center will release another update in early October, and if El Nino conditions develop in the coming months, the current El Nino Watch will be upgraded to an El Nino Advisory which could last through early spring.