As state prepares for hurricane season, past flood disasters offer glimpse of warmer future

HONOLULU (HawaiiNewsNow) - Hurricane season officially begins Friday.

Forecasters say the Central Pacific could see three to six tropical cyclones that would bring torrential rains, strong winds and severe flooding.

This all comes as the state is still recovering from a record-breaking winter storm that pummeled parts of Oahu and Kauai in April.

Heavy rains triggered floods and mudslides that made major roads inaccessible, destroyed and stranded cars, and ripped homes from their foundations. Some 532 homes were damaged or destroyed in the event, and the amount of rainfall — nearly 50 inches in a 24-hour period — could break a national record if verified.

"It was record-breaking flooding and that's a big difference because it's not the total amount of rain you get, it's how that rain falls," said Kevin Kodama, meteorologist with the National Weather Service. "It's the intensity that really makes a difference for flash flooding."

As hurricane season begins, forecasters stress it only takes one big storm to leave behind significant damage.

"One tropical cyclone that affects you directly could really wreck your whole year and you're gonna have a long time to rebuild and you need to be prepared for that," said Bob Ballard, also of the National Weather Service.

And the islands already saw something similar with the April flooding event: That unforgettable image of cars under water and homes toppled over.

Experts say this image serves as an important reminder for what the islands could see more of by the end of the century as a result of climate change: more storms and more intense storms that might not only happen more regularly, but could become the norm.

"It's very gradual, and just because we had a record-breaking event doesn't mean next year we're going to have that again," said Steven Businger, professor of meteorology at the University of Hawaii. "But the state will have more record floods in the future."

Storms and warm waters

The April storm came as part of a busy wet season in which the islands experienced a strong La Niña event -- or a period in which most of the tropical Pacific Ocean is cooler than average.

And now, the islands face a completely different threat as hurricane season arrives: tropical cyclones.

Businger stressed that tropical cyclones and winter storms are "different animals."

April's storm fed on temperature gradients and instability. Tropical cyclones, on the other hand, typically get their energy from heat emitted from the top of the ocean, and can cause devastation with powerful winds and heavy rainfall.

But both types of storms can cause major flood damage. And both can be affected by sea surface temperatures.

That's a concern because, studies show, sea surface temps have been rising by 0.13 degrees Fahrenheit per decade since 1880.

Scientists predict warmer water temperatures, linked to a warming planet, will lead not only to stronger storms, but more frequent ones.

And warmer water could also change a storm's track, bringing it closer to the islands.

"The connection between global warming and increasing in strength of hurricanes or changing in the paths of hurricanes … that's really clear because it's driven by the sea surface temperatures," Businger said.

In fact, a recent report by the Intergovernmental Panel on Climate Change suggests that climate change will likely increase the frequency and intensity of heavy rainfall events this century, particularly for tropical regions like Hawaii. This also includes heavy rain associated with tropical cyclones.

A past with destructive storms

Scientists say climate change could lead to more and stronger El Niños -- a natural recurring warming in the equatorial Pacific Ocean that influences air and moisture movement around the globe.

Hawaii saw some of those effects from El Niño, like in 2015, which was a record-breaking hurricane season with 15 tropical cyclones raging through the Central Pacific, some coming eerily close to the state.

And a year later, Tropical Storm Darby, which made landfall on the Big Island, also hammered some of the other islands with torrential rain that flooded homes, triggered numerous sewage spills and also swamped the H-1 Freeway on Oahu, disrupting thousands of commuters.

Regardless of the type of storm -- whether it's a tropical cyclone or a winter storm like the one that happened most recently in April -- the flood damage left behind could become a familiar sight if the earth continues to warm at its current pace, experts say.

And the warming is exponential, meaning that the changes will start off gradual, but as time goes on, the results get worse.

"It's bound to happen again, and toward the end of the century, it's definitely going to happen more often because of the exponential nature of the warming," Businger said. "It's like a bank account that has good interest. It's compounded all the time."

Global warming 'pushed the extreme'

Businger said the flood event that happened on Kauai was an anomaly, but it took just the right meteorological conditions to create what he calls "the perfect storm."

But it's important to note that global warming didn't necessarily cause the April event, he said, because this is just how weather works. However, global warming might have pushed the extreme, he said.

"In other words, it might have rained a little less if the same meteorological conditions occurred 20 years ago or 30 years ago, so there is a marginal influence from the global warming," Businger said.

Yuqing Wang, professor of meteorology at the University of Hawaii, adds that it was an event triggered primarily by La Niña. But the cold air mixed with the warmer sea surface temperature resulted in an unstable atmosphere.

"They bring such extreme events because the sea surface temperature is really high around Hawaii," he said. "About 2 degrees higher than normal."

Planning ahead for climate change

Michael Foley, coastal engineer at Oceanit, an engineering consulting firm based in Honolulu, said the devastation that resulted from the Kauai flooding served as an important reminder of what could happen in the future as the state braces for more of these flooding events as a result of climate change.

"We saw the amount of coastal erosion, the impacts that increased water level might have on a community," Foley said. "I think that was a preview into the future of what we can expect, and it can get much worse than that."

Grant Tokumi, who also works with Oceanit as a civil engineer and flood specialist, said as these storms become frequently recurring events, communities need to be more vigilant and proactive when planning ahead for the effects of climate change.

The April event was the perfect opportunity for people to look ahead.

"In those kind of areas, maybe they should ask the question, should I buy flood insurance? Just because they're not required to buy flood insurance doesn't mean that it's not going to flood," Tokumi said.

There are parts of the island that aren't in the floodplain, he said, but it doesn't mean that those areas won't flood – it just means that the area hasn't been analyzed. Plus, many of the original flood maps were created in the 1940s, when climate change wasn't accounted for, so that's something that homeowners should be thinking about as they plan ahead.

Adding to that, Foley said people simply need to be aware of what climate change means for them and how it will affect the long-term viability of their investment.

"For a lot of people in Hawaii, that's their pride and joy is their property that they're going to pass on to the next generation," he said. "And the next generation is going to have to deal with an increasing amount of effects of climate change."

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