El Niño On The Horizon

The SOI has swung abruptly negative, one of the indicators that suggest a developing El Niño:

The recent evolution of climate patterns across the equatorial Pacific is consistent with the early stages of a developing El Niño. Moreover, during the past few months computer forecasts have increasingly shown El Niño as a distinct possibility for 2009. The odds of an El Niño are now thought to be above 50%, which is more than double the normal risk of an event. However, it is still possible that the recent trends may stall without El Niño thresholds being reached.

Since the start of April, surface temperatures across the equatorial Pacific have risen by about 0.8°C and now stand at around 0.5°C above average (the El Niño threshold is 0.8°C above average). In addition, there has been a marked warming below the surface and the Southern Oscillation Index (SOI) has dropped to around −7. Also, the Trade Winds were weaker than normal over much of the tropical Pacific from late April to late May. However, patterns of Pacific cloud haven't as yet shown any clear trends towards El Niño: this indicates that the ocean-atmosphere coupling which amplifies and maintains El Niño isn't established.