Ocean Temperatures Reach El Niño Threshold

For the first time since the fall of 2012, weekly-averaged sea surface temperatures (SSTs) in the equatorial Pacific have reached the threshold needed for an El Niño event to be declared. By definition, an El Niño episode occurs when SSTs are at least +0.5°C from average for three consecutive months in the region 120°W - 170°W, 5°S - 5°N (called the Niño 3.4 region.)

The weekly ENSO update issued by NOAA on May 12, 2014, put ocean temperatures in this Niño 3.4 region for the past seven days at +0.5°C from average. An El Niño event is still not a sure thing, though. We saw similar behavior in the fall of 2012, with SSTs warming up above the +0.5°C threshold, prompting NOAA to issue an El Niño Watch. However, the ocean SSTs were not able to hold for the required three month period, and no El Niño event ended up happening. However, this year the odds appear more favorable.

NOAA has issued an El Niño Watch for the summer and fall of 2014, giving a greater than 65% chance that an El Niño event will occur during summer, a boost upwards from their >50% chance given the previous month. The May 8 El Niño discussion from NOAA's Climate Prediction Center noted that "There remains uncertainty as to exactly when El Niño will develop and an even greater uncertainty as to how strong it may become. 

This uncertainty is related to the inherently lower forecast skill of the models for forecasts made in the spring." None of the El Niño models (updated in mid-April 2014) predict La Niña conditions for peak hurricane season, August-September-October 2014, and 16 of 20 predict El Niño conditions. There is currently not a strong Westerly Wind Burst (WWB) over the equatorial Pacific Ocean helping push warm water eastwards towards South America. There have been three of these WWBs so far in 2014, and if we get one more in the next month or two, that should be enough to push the system into a full-fledged El Niño event.

 

Figure 1. Departure of sea surface temperature (SST) from average for May 12, 2014. A plume of warmer-than-average temperatures stretched along the equatorial Pacific from the coast of South America westwards into the Western Pacific, a harbinger of a developing El Niño event. Image credit: NOAA.

El Niño events usually lead to quiet Atlantic hurricane seasons

El Niño conditions tend to make quieter than average Atlantic hurricane seasons, due to an increase in upper-level winds that create strong wind shear over the Tropical Atlantic. The last official El Niño event occurred from summer 2009 - spring 2010, and as expected, the 2009 Atlantic hurricane season was a relatively quiet one, with 11 named storms, 3 hurricanes, and 2 major hurricanes. No 2009 hurricanes got their names retired, and there were only six fatalities.