“Days like today, in a situation like this, we just throw open the doors and hold on for the ride,” said Scott Ankrom, who works at a Costco in Hawaii, where customers are scrambling to stock up for some serious weather.
The situation in Hawaii is this: two Category 1 hurricanes are nearing the mainland, one right after the other. The 85 mph-wind Hurricane Iselle is expected to hit Thursday, followed by the 75 mph-wind Hurricane Julio three days later. Both are expected to weaken to tropical storms before they hit. But the back-to-back event is rare, which undoubtedly poses the question to some: is this because of climate change?
The answer, in short, is that it’s impossible to tell.
“Hurricanes in Hawaii are so rare that it will take decades before we see enough storms affecting them so that we can say there’s a statistically significant climate change signal,” Jeff Masters, director of meteorology at Weather Underground, told Climate Progress on Wednesday. “Ocean temperatures where Iselle and Julio are crossing are about 1°C warmer than average, so we can say a warmer ocean made this event more likely.”
Tropical storms of this magnitude are very common in Pacific Ocean waters surrounding Hawaii, especially now that it’s hurricane season. What makes this event rare is the fact that Hawaii is such a small target in such a vast, active ocean. Hurricanes don’t often hit Hawaii — not only because of its small size but because of cool ocean temperatures and dry air that generally surround the island.
For two hurricanes to hit so closely together is “unprecedented,” Weather Channel meteorologist Kevin Roth said, noting that the most similar event was two weak tropical storms hitting Hawaii in 1982. Those storms were separated by 10 days.
Both events on their own have little to do with climate change. But what Masters wants people to take note of is that, over time, global warming is expected to increase tropical storms and hurricanes in Hawaii. He cites a 2013 modeling study published in the journal Nature Climate Change, which found exactly that.
“From 1979 to 2003, both observational records and our model document that only every four years on average did a tropical cyclone come near Hawaii,” the Nature study’s lead author Hiroyuki Murakami said in a press release about the study. “Our projections for the end of this century show a two-to-three-fold increase for this region.”
Masters notes that Murakami’s research doesn’t show that there will be more storms in the Pacific — just that more storms will actually reach Hawaii’s shores when global temperatures are 2°C (3.6°F) warmer than today. That’s because of factors such as a northward shift in where the storms usually form, due to warming waters.
Right now, ocean surface temperatures in the North Pacific Ocean are warmer than just about everywhere — though atmospheric scientist Jennifer Francis notes that that’s partially due to more El-Niño-like conditions.
“But there’s also a component due to global warming,” Francis, a research professor at Rutger’s Institute of Marine and Coastal Sciences, said. “During El Niño years we tend to see more hurricanes in the neighborhood of Hawaii, and the generally warmer sea surface temperatures due to climate change would also favor tropical storm development in the eastern Pacific.”
The link between warming and hurricanes is, at the moment, scientifically indefinite. The U.N.’s Intergovernmental Panel on Climate Change has indicated that it does not yet have strong evidence to suggest notable increases in the number of hurricanes due to human-caused global warming. There has been increasing evidence, though, that rising sea levels are upping the potential destruction of storm surges, which would make tropical storms more dangerous.
It’s been an active hurricane season in Hawaii’s surrounding waters, too. As Masters notes, the area has so far in 2014 seen 10 named storms, 4 hurricanes, and 3 intense hurricanes so far in 2014. On average, the Eastern Pacific is expected to see 6 named storms, 3 hurricanes, and 1 intense hurricane by August 4.
But even with this year’s increases and the number of increases projected in the future by the Nature study, the number of hurricanes striking Hawaii is still too low to make a definitive climate statement.
“The yearly number we project … still remains very low,” study co-author Bin Wang said. “With such a low incidence of storms, it will be very difficult to determine if they are indeed changing due to a changing climate without several decades of data.”