Hurricane Ophelia: What a Tropical Storm Is Doing in Europe

The forecast for Hurricane Ophelia, as of Friday morning. National Hurricane Center

Hurricane Ophelia, now a Category 2 storm, is the 10th hurricane in this Atlantic storm season. But rather than follow the pack and travel first west, then north, then northeast, circling the Atlantic one way or another, Ophelia is going its own way. First it meandered westward, then this week turned northwest.

Currently, early forecasts suggest it will approach Ireland on Monday—not making landfall as a hurricane per se, but packing hurricane-strength winds. (These are very early forecasts with lots of potential to change over the intervening days, as both the Irish and British weather agencies note.)

Ophelia's destination isn't unprecedented, but the storm is still raising eyebrows, says Reindert Haarsma, a climate scientist at the Royal Netherlands Meteorological Institute. "A number of [tropical storms] reach Europe, but usually they are weak systems," he told Newsweek. "That they reach Europe with this strength, near hurricane force, is quite unusual."

Whether or not Ophelia is carrying hurricane-force winds, it won't actually be a hurricane by about Sunday morning. That's because a hurricane is built around a core of warm, moist air. Spend too long over cooler water from, say, traveling north, and a storm has two potential fates—either it falls to pieces or it undergoes what's called an "extratropical transition," a meteorological metamorphosis.

During an extratropical transition, the warm core of the storm keeps feeding its strength, but the storm also pulls energy from a second source: the difference in temperature between its northern and southern sides, which is the same mechanism that powers normal autumn storms away from the equator. Sometimes an extratropical storm still fades away, but sometimes the pair of energy sources causes the storm to reintensify, as Ophelia is predicted to do.

"There's a lot of things that have to fit well to provide the circumstances for reintensification and they all have to work together," Haarsma says. "That is why it is so rare." A storm needs the perfect combination of factors like its location and temperatures at the surface of the ocean in order to pull off reintensification. "Usually they die and they don't get that strength before they enter Europe," Haarsma says.

But when storms do manage the feat, it's never good news. "There's a big concern not only for the people and infrastrucure, but also the environment," Haarsma says, because these regions don't see this type of strong storm regularly. "The trees are still full of leaves, so they are very vulnerable to large big storms," Haarsma says, adding that unlike trees in, say, Florida, they tend to break rather than bend when hit by strong winds.

The last former hurricane to cause serious problems in Europe was Gonzalo in 2014, which struck the United Kingdom on October 21 after becoming an extratropical storm. But according to calculations by Haarsma and his colleagues and similar work by a second team, the phenomenon will become more common as climate change continues.

Someday soon, Ophelia may not be nearly as surprising as it is today.