Key differences between the 1997 and 2015 El Nios, and their impact on our hurricane season

The 1997 and 2015 El Niño events are very similar in many ways — mainly in their stark intensity. But over the North Atlantic ocean, interesting differences emerge between the 1997 record-strong El Niño and its potential usurper.

Just past the halfway point, this Atlantic hurricane season has been relatively quiet. Hurricane activity is just 40 percent of normal for this time of year. El Niño, which is defined by the presences of warmer than normal ocean temperatures in the tropical Pacific, is primarily responsible for the quiet hurricane season, through its influence on the upper-level wind patterns over the Atlantic Ocean.

Research has shown that the location of the warmest Pacific ocean waters can possibly lead to different effects on weather across the globe. During the 1997 El Niño, the warmest ocean temperatures were located in the far eastern Pacific and peaked in mid-September. During this El Niño, on the other hand, the warmest waters have been concentrated west of that, in the central tropical Pacific, with warmer waters than 1997 in the central tropical Pacific. Another interesting difference is the emergence of very warm water in the northeast Pacific and around Hawaii — a feature often referred to as “the blob.”

In the Atlantic Ocean, sea surface temperature is also different between the two El Niño years. While 1997 was characterized by approximately ocean temperatures across most of the tropical Atlantic, temperatures in the far eastern tropical Atlantic have been much warmer than normal this year, which is likely one of the reasons why we have seen several tropical cyclones form in the far southeastern part of the basin so far. In 1997, only one tropical cyclone formed in this region, while the remaining seven storms developed to the north, or closer to the East Coast.

Perhaps the most interesting difference between the 1997 and 2015 El Niños has been the pattern of wind shear across the Atlantic Ocean. Wind shear, which is the change in wind direction and speed as you go up in the atmosphere, is harmful to blossoming hurricanes. El Niño typically brings strong upper-level westerly winds across the Caribbean, extending into the tropical Atlantic, which rips apart storms as they travel from east to west in the deep tropics.

The 2015 season has been characterized by the strongest levels of vertical wind shear on record for the Caribbean, which is a primary reason why we’ve seen no tropical cyclones develop in the Caribbean this year. However, farther east in the tropical Atlantic, vertical wind shear is actually below-normal, which is another reason why tropical cyclones have been able to form there.

In 1997, on the other hand, vertical wind shear was above-average across the entire tropical Atlantic, which is likely why all of the storm activity that year (with the exception of Erika) formed outside of the deep tropics.

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In the later half of the season, hurricane activity tends to favor the areas around the Caribbean — the same location where wind shear has been extraordinarily strong this year. So it looks like the end of the 2015 Atlantic hurricane season will be below average.

While both 1997 and very likely 2015 will go down in the record books as well below-average hurricane seasons in the Atlantic, the two strongest El Niños since 1950 have exhibited considerably different responses in both Atlantic climate patterns as well as Atlantic hurricane formation locations.

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