Hurricane season was average but deadly
The 2023 hurricane season officially draws to a close Thursday, extending to five years a run of average to below-average Central Pacific hurricane seasons.
However, this year’s season will be forever remembered for its link to the origin of the deadly Maui wildfires.
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That connection is so strong that the Central Pacific Hurricane Center will ask an international committee on hurricane names to retire the name Dora in perpetuity, arguing that it would be insensitive to use it again.
The odd thing is that Category 4 Dora never came closer than 500 miles to Hawaii. Although a major storm, its system was relatively small, with tropical storm-force winds extending out only 100 to 200 miles.
How did this remote storm help generate the winds that drove the deadliest wildfire in U.S. history in more than a century?
The key was the vast area of deep low pressure created by the storm and a strong area of high pressure north of the state. When these phenomena clashed, conditions led to the winds whipping down the mountainsides with gusts of 60 mph or more.
Alison Nugent, associate professor of atmospheric sciences at the University of Hawaii at Manoa, said the same atmospheric conditions that guided Dora, as well as the enhanced pressure gradient from the storm, likely strengthened the winds and worsened the fire impacts.
Dora’s role also likely led to strengthening the tradewind inversion, thereby priming the environment for a downslope windstorm, she said.
Nugent’s 2020 study, “Fire and Rain: The Legacy of Hurricane Lane in Hawai‘i,” was the first to document the link between a tropical cyclone and wildfire in the islands. Lane, in 2018, helped to generate winds that drove a fire that destroyed 21 structures in West Maui.
“Dora’s winds were exactly the same as the setup for Lane. Mirror images. Storm south of the island, winds enhanced, subsidence over the islands driving downslope winds in the lee,” Nugent said in an email. “The primary difference to me is that Dora caused even stronger winds and even drier conditions that lasted longer (thereby making the fires even harder to fight).”
But there were other similarities, she said. They both occurred in El Nino years. Both saw an extremely wet season preceded by an extremely dry season just before the event, leaving lots of parched brush as fuel for fire. And both had ferocious winds that made it impossible to fight fires by helicopter.
This hurricane/fire connection is likely to be a growing phenomenon. In a recent seminar at UH, Hono lulu meteorologist Derek Wroe of the National Weather Service noted that another 2018 hurricane, called Hector, also was linked to fires on Hawaii island and Oahu, blackening 10,000-plus acres between them.
Wroe showed a slide image of billowing smoke on the Big Island, saying, “It’s probably one of the biggest wildfires you never heard of.”
As for the 2023 hurricane season, John Bravender, warning coordination meteorologist with the Central Pacific Hurricane Center, said that on the surface it was an average year, with four tropical cyclones in the Central Pacific Basin.
