ENSO Blog

Many people are interested in knowing which ENSO category (La Niña, neutral or El Niño) is expected by the climate experts, just as they might want to know the weather forecast for tomorrow. They usually prefer a simple answer—one with little or no uncertainty. Unfortunately, however, weather and climate forecasts are never about certainty: they’re about probability. Using probabilities allows us to describe the uncertainty in quantitative terms. If there were no uncertainty about what the climate would be like in the future, then one outcome would be given a 100% chance of occurring, while any other outcome(s) would have a 0% chance. While probabilities near 0% and 100% often occur in as…   Read article

By this point, most of you have heard that it looks like El Niño is coming, and maybe you’re wondering why you should care.  After all, why should it matter if the tropical Pacific Ocean becomes warmer than average? That’s thousands of miles away from the continental United States.  Well, it turns out that El Niño often results in changes in the patterns of precipitation and temperature across many parts of the globe, including North America (Ropelewski and Halpert 1987, Halpert and Ropelewski 1992). Many folks probably remember the heavy rainfall, flooding, and landslides that occurred in California in 1982/83 and again in 1997/98. As the region suffers through a devastati…   Read article

Today, the Climate Prediction Center (CPC) released the June ENSO Diagnostic Discussion.  Chances that an El Niño will occur by summer are above 70%, and reach 80% by the fall. Sea-surface temperature anomalies increased across all the Niño index regions in May; the latest weekly value of the Niño3.4 index is now above +0.5°C. Tropical rainfall across Indonesia and the Pacific remain close to average, but forecasters are confident that the atmosphere will begin to respond to the ocean and El Niño will develop, likely in the next few months. Recently, there’s been a lot of speculation about how strong this El Niño will be, especially considering the strong westerly wind bursts in late…   Read article

With the approach of the 2014 hurricane season and the strong potential for El Niño to develop during the next few months, the effect that El Niño has on both the Atlantic and Pacific hurricanes seasons is worth exploring. The hurricane impacts of El Niño and its counterpart La Niña are like a see-saw between the Pacific and Atlantic oceans, strengthening hurricane activity in one region while weakening it in the other.   Simply put, El Niño favors stronger hurricane activity in the central and eastern Pacific basins, and suppresses it in the Atlantic basin (Figure 1). Conversely, La Niña suppresses hurricane activity in the central and eastern Pacific basins, and enhances it …   Read article

If you pick up a stack of journals on ENSO you will quickly discover that most scientists define ENSO based on “seasons” ( 3-month averages) of oceanic and atmospheric indicators in the tropical Pacific.  Why is that?     See this figure of the weekly sea surface temperature (SST) anomalies (departures from average) in the Niño-3.4 region, an area in the east-central equatorial Pacific Ocean?  The values wobble around a bit.  In fact, if you were to look at weekly values based on atmospheric pressure anomalies at the surface (the Equatorial Southern Oscillation index), they bounce around a lot more.  This time series is clearly “noisy.”  …   Read article