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• RISK OF RAIN 3 DECEMBER 2018 PATCH

Coastal El Niño events can also spread west, preceding El Niño conditions in the Niño-3.4 region, so it’s something to keep an eye on. ENFEN (Peru’s commission on ENSO) recently issued a notice about the potential for a Coastal El Niño, an event which can have very significant consequences for rainfall in Peru.

RISK OF RAIN 3 DECEMBER 2018 PATCH

In the sea surface temperature animation above, you might notice a red patch growing off the coast of Peru in recent weeks. If we don’t have an El Niño in 2023–24, that will be five years! However, 73 years is a short record for a phenomenon that has decade-to-decade variability, so this is more of an interesting factoid than anything. One fun little nugget of information is that, in our historical record dating back to 1950, we have not gone more than four years in a row without an El Niño. However, the spring predictability barrier, together with the still somewhat-La Niña-ish atmosphere and the lack of strong physical signs such as a large amount of warmer-than-average subsurface water in the tropical Pacific, mean we’re not yet hoisting an El Niño Watch. Our forecaster consensus does reflect the increased chance of El Niño, with chances around 60% by the fall. Blue bars show the chances of La Niña, gray bars the chances for neutral, and red bars the chances for El Niño. NOAA Climate Prediction Center forecast for each of the three possible ENSO categories for the next 8 overlapping 3-month seasons. (Why do ENSO events peak in the winter? This is a really complicated topic that we don’t have a simple, satisfactory answer to… (yet!) However, right now is a very tricky time of year for the models, due to the “ spring predictability barrier.” ENSO events peak in the winter and tend to decay and transition in the spring, so models often don’t have a lot of strong signals to go on.

Many of our computer climate models are predicting a transition into El Niño sometime later this year. The lack of El Niño or La Niña means that there is no seasonal-scale influence from the Pacific to push around the global atmospheric circulation and influence seasonal climate patterns. In contrast, a continuation of neutral conditions means the tropical Pacific Ocean will not be an actor on the world’s climate stage. We know what you’re really interested in, though-will El Niño develop? If we can anticipate an El Niño, we can anticipate an increased likelihood of its impacts on weather and climate. The forecaster consensus is indeed very confident that neutral conditions will remain through the spring. Once the tropical Pacific ocean-atmosphere system is showing signs of decoupling, such as a monthly Niño-3.4 index value warmer than -0.5 ☌, we can say that neutral conditions have likely arrived. The same is not true for neutral conditions, however. We’re often going on and on here at the ENSO Blog about how ENSO is a seasonal phenomenon, meaning the ocean and atmosphere criteria must be met for several consecutive months in order to qualify as La Niña or El Niño. In February, after nearly a year at or above 1.0, the EQSOI was just 0.1 This tells us that at least one element of the atmospheric La Niña response has weakened. When this index is positive, it indicates that the Walker circulation is amped up. One measure of the atmospheric component of ENSO is the Equatorial Southern Oscillation Index (EQSOI), which measures the relationship between surface air pressure in the western and eastern Pacific. However, without the cooler sea surface characteristic of La Niña, it’s likely this pattern will diminish in the coming weeks. The atmosphere is a little more complicated, as it tends to be! We still see some indications of a La Niña-like strengthened Walker circulation, with more rain and clouds than average over Indonesia, less over the central Pacific, and enhanced trade winds. Description of historical baseline period. Graphic by, based on data from NOAA’s Environmental Visualization Lab. East of the International Dateline (180˚), waters remained cooler than average, a sign of La Niña. Sea surface temperatures in the tropical Pacific Ocean from early January through early March 2023 compared to the long-term average.