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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 winter, and the large subsurface temperatures in early spring. The subsurface temperatures in March, which was a record for the month going back to 1979, inspired comparisons to the early stages of the 1997/98 El Niño, the largest on record (ONI maximum of 2.4). That event also developed in the spring, like this one. However, right now, forecasters are not favoring a strong event (while not at all ruling it out) and believe a moderate event (ONI 1.0 – 1.5) is slightly more likely, sometime during the fall/winter. So what’s going on?