Hurricane season’s quiet start turns weird: Fiona, Ian and climate change’s effects on the strongest storms

This year’s Atlantic Ocean hurricane season has had a distinct whiplash vibe.

“It has been an unusual year,” said Phil Klotzbach, a senior research scientist and hurricane expert at Colorado State University. “We had no named storms in August for the first time since 1997, and since then we’ve had six named storms, four hurricanes and two major hurricanes.”

Climate change is undoubtedly altering hurricanes and their traditional season in a number of ways that often combine to make the storms more damaging than in the past. But Klotzbach said this particular off-and-on season is more likely due to natural variability. Hurricanes are big, relatively infrequent events, and up or down years, or strangely clustered storms, don’t say much about the changing climate on their own. He pointed out that the four quietest Septembers in a row — Sept. 10 marks the climatological peak of the Atlantic hurricane season — came between 2013 and 2016, and then each September since 2017 has seen well-above-average activity.

This year, specific conditions in August — in particular, strong wind shear, the change in wind direction and speed across varying altitudes — made it difficult for tropical storms to form. “In September, we’ve had much more conducive conditions, with shear running near to below average,” Klotzbach said. “Midlevel moisture has also increased somewhat, allowing for conditions where hurricanes can develop and thrive.”

Bigger, stronger, faster

The total number of Atlantic tropical cyclones has not increased dramatically over the last few decades.

Why is that? For one, climate change appears to be helping them get stronger, faster.

Two of the three most damaging U.S. hurricanes in history, both in 2017, underwent such rapid intensification. Hurricane Harvey struck the Houston area, causing $125 billion in damage, after intensifying from a tropical storm all the way to a Category 4 hurricane over the course of less than two days. The next month, Hurricane Maria’s wind speeds nearly doubled, going from a Category 1 storm to Category 5 in under 24 hours just before slamming into Puerto Rico.

New research that is yet to be published, Balaguru added, will show that such rapid strengthening in the “near-coastal” region is also now occurring more frequently, meaning even a relatively slow-moving hurricane is more likely to ramp up in power just before landfall, catching a city or region by surprise.

A riskier hurricane landscape

The potential for near-shore rapid intensification, Balaguru said, can also be blamed on climate change, with an increasing contrast in temperatures over land and sea. “This has lots of implications for decision-makers, people living in coastal regions, critical coastal infrastructure and for operational forecasting,” he said. “These conditions will also increase the change of flooding after landfall.”

Taken together, climate change is obviously altering hurricanes enough to make them even more dangerous than in the past. As Puerto Rico struggles to restore power and Florida battens down the hatches and waits, that has never been more clear.