Editor’s Note — This piece originally ran on September 22, 2018.
The upcoming hurricane season brings with it with a number of concerns, one of which is the timing of a mega El Niño, weather patterns that tend to bring heightened hurricane activity.
According to a graphic published recently by CNN (an earlier version ran on Friday, March 8), it looks as though El Niño could soon be turning into a La Niña. However, the key variable to watch as the hurricane season looms is the presence of an Arctic Oscillation, a weather pattern that influences the Atlantic and Pacific regions. El Niño and La Niña typically lead to spikes in rainfall over the tropics.
An Arctic Oscillation Monitor predicts the cyclical change in the atmospheric circulation and is expected to be relatively weak in 2019. However, it will eventually evolve into a more active pattern, bringing with it increased hurricane activity and more outbreaks of summer storms like Harvey, Hurricane Irma and Hurricane Maria.
“[La Niña] is tied to the Atlantic and the extent of that warming over the top of the world is critically important to the forecast,” CNN meteorologist Allison Chinchar said.
La Niña is characterized by a sea surface temperature anomaly of 0.5 degrees Celsius or more in the equatorial Pacific and a weak or medium-sized global warming signal.
Although La Niña is sometimes associated with a reduction in tropical cyclone activity, another effect can be a weakening of the high-energy winds associated with El Niño and a prolonged, stable atmospheric circulation.
The last La Niña year was 1998, when there were 15 named tropical storms, 10 hurricanes and five major hurricanes. The last major hurricane was Hurricane Frances, which hit Florida in September of that year.
CNN Meteorologist Allison Chinchar expects an active Atlantic hurricane season. With six to nine named storms, including between two and five hurricanes, experts believe that the 2017-2018 season could be classified as active. (The most active Atlantic season of all time was 2015, when there were 18 named storms, including 10 hurricanes.)
“This is one of the busier seasons,” Chinchar said. “While you don’t see the intensity, that’s another important change with the Atlantic because of increased heights in eyewall,” she said. “They can get stronger.”
In addition to a strong El Niño, warmer than average temperatures will also play a role in this year’s Atlantic hurricane season. On the El Niño watch is the “temperature pattern” rather than the trend of the water temperatures.
According to Chinchar, these two factors will dominate the season’s activity.
“This is a warm ocean’s year so El Niño is not going to be a big problem. El Niño is going to be a larger hindrance if the warmth in the stratosphere. “