A major marine heat wave is responsible for a triple-digit number of record high heat days in Hawaii this summer, according to the National Weather Service.
Hilo International Airport saw 16 days where record high temperatures were either set or tied during the summer that ended Monday. The tally of record heat days was even higher at the airports in Honolulu, Kahului, Maui, and Lihue, Kauai — 24, 40 and 48, respectively.
On Sunday, summer’s last day, Hilo set a record high with 90 degrees, edging out the previous record of 89 degrees set for the date in 1995.
Fall arrived in record fashion as well, as Kahului registered a 94-degree day, tying its previous record high for the date set in 1993.
According to the National Oceanographic and Atmospheric Administration, the heat wave’s causes include a persistent low pressure weather pattern between Hawaii and Alaska that weakened winds that otherwise might mix and cool surface waters across much of the North Pacific.
What’s causing that is unclear: It might reflect the atmosphere’s usual chaotic motion, or it could be related to the warming of the oceans and other effects of human-made climate change.
“It’s been the culprit for the really warm summer that we’ve had. It’s been what’s causing us to break records on a nearly daily basis,” said Derek Wroe, meteorologist at the National Weather Service in Honolulu. “The ocean’s been several degrees warmer than normal the entire summer — and that’s what’s been pushing our temperatures up several degrees higher than normal. It’s projected to stay that way, at least for the next several months. And so we can continue to see warmer than normal conditions through that time.”
Wroe said he’s surprised Lihue has seen three times as many record highs as Hilo.
“They’re both windward sites,” he said. “Even though the ocean is warmer than normal, the windward sides tend to have their weather modified by the breezes and because it’s a little more cloudy than other places. That, would usually keep it from breaking as many (heat records) as other places.”
In addition to the human discomfort, there is an environmental toll caused by the warmer oceans. Researchers using high-tech equipment say Hawaii’s coral reefs are showing damage from the hottest ocean temperatures ever recorded around the Hawaiian Islands in June, July and parts of August. So far in September, oceanic temperatures are below only those seen in 2015.
“In 2015, we hit temperatures that we’ve never recorded ever in Hawaii,” said Jamison Gove, an oceanographer with the NOAA. “What is really important — or alarming, probably more appropriately — about this event is that we’ve been tracking above where we were at this time in 2015.”
The marine heat wave four years ago killed nearly half of West Hawaii’s coral. And federal researchers are predicting another round of hot water will cause some of the worst coral bleaching the region has ever experienced.
Forecasters expect high temperatures in the North Pacific will continue to pump heat into Hawaii’s waters well into October.
“Temperatures have been warm for quite a long time,” Gove said. “It’s not just how hot it is — it’s how long those ocean temperatures stay warm.”
Coral reefs are vital around the world as they not only provide a habitat for fish — the base of the marine food chain — but food and medicine for humans. They also create an essential shoreline barrier that breaks apart large ocean swells and protects densely populated shorelines from storm surges during hurricanes.
In Hawaii, reefs are also a major part of the economy: Tourism thrives largely because of coral reefs that help create and protect white sand beaches, offer snorkeling and diving spots and help form waves that draw surfers from around the world.
“You have things like two giant volcanoes on the Big Island blocking the predominant trade winds,” making the island’s west coast one of the hottest parts of the state, according to Gove. He said he expects “severe” coral bleaching in those places.
“This is widespread, 100% bleaching of most corals,” Gove said.
And many of those corals are still recovering from the 2015 bleaching event, meaning they are more susceptible to thermal stress.
In West Hawaii’s remote Papa Bay, most of the corals recovered from the 2015 bleaching event, but scientists worry they won’t fare as well this time.
“Nearly every species that we monitor has at least some bleaching,” said ecologist Greg Asner, director of Arizona State University’s Center for Global Discovery and Conservation Science, after a dive in the bay earlier this month.
Asner said sensors showed the bay was about 3.5 degrees above what is normal for this time of year.
While the ocean heat itself is expected to continue for awhile, Wroe said, “We will cool off.”
“It’s a seasonal thing,” he said. “The sun angle’s getting lower. We’re not going to get as much heat … from the sun. So we’ll see a decrease in our daytime high temperatures, but they’ll also be several degrees warmer than normal. In a month or so, it’s usually in the mid 80s. It’ll probably be several degrees warmer than that, but we won’t stay as warm as we have been. That’s due to the warmer than normal ocean and the sun angle. That’s what allows us to get so warm in the summertime, anyway. So as we get toward wintertime, we’ll cool off, but we just won’t see temperatures as cool as we’re used to seeing it.”
While people likely will catch a break from the heat as autumn progresses toward winter, scientists will use information they’re gathering to research, among other things, why some coral species are more resilient to thermal stress. Some of the latest laboratory research suggests slowly exposing coral to heat can condition them to withstand hotter water in the future.
“After the heat wave ends, we will have a good map with which to plan restoration efforts,” Asner said.
He uses advanced imaging technology mounted to aircraft, satellite data, underwater sensors and information from the public to give state and federal researchers such as Gove the information they need.
“What’s really important here is that we’re taking these (underwater) measurements, connecting them to our aircraft data and then connecting them again to the satellite data,” Asner said. “That lets us scale up to see the big picture to get the truth about what’s going on here.”
The Associated Press contributed to this story.
Email John Burnett at jburnett@hawaiitribune-herald.com.