The deadliest and most destructive U.S. wildfires of 2023 thus far swept through Hawai‘i on Tuesday night and Wednesday, Aug. 8-9. At least 36 deaths had been reported from the fires by early Thursday, with an uncertain number of people injured.
The worst damage was on Maui, where the central part of Lahaina (pop. 12,000) was largely destroyed. More than 271 structures in Lahaina had been affected, Maui County authorities reported in a news release late Wednesday. Two other blazes, the Upcountry and Pūlehu fires, destroyed several homes elsewhere on Maui. Three fires were in progress on the island of Hawai‘i, but no injuries or structural losses had been reported by late Wednesday, according to the Associated Press.
Aerial images showed fire-charred structures throughout the core of Lahaina, which served as the capital of the Hawaiian Kingdom from 1820 to 1845. Most of the town is part of a National Historic Landmark District, with a number of buildings dating back 150 to 200 years. Damages to Lahaina could well run into the hundreds of millions of dollars, if not even more, likely making it the worst natural disaster in state history since Hurricane Iniki caused $6.7 billion in damage in 1992. The loss of two centuries of civic and architectural history, and the psychic impact of the fire on Maui residents, are incalculable.
The flames that tore across Maui were fanned by winds gusting from 40 to 80 mph, driven by an expansive and unusually strong high-pressure cell that was intensifying to the north of Hawai‘i. At the same time, Category 4 Hurricane Dora was passing well to the south of Hawaii, and the contrast between Dora and the surface high only added to a sprawling area of strong easterly winds. These easterly winds warmed, dried, and intensified as they descended the West Maui Mountains and swept into Lahaina. Such mountain downslope winds have fueled some of the most destructive wildfires in recent U.S. history, including Colorado’s Marshall Fire of Dec. 30, 2021, and several of the worst Santa Ana and El Diablo fires on record in California.
Did Hurricane Dora play a role in the Hawai‘i wildfires?
It’s an open question how much the presence of Dora may have fueled the strength of the winds that ripped across Hawai‘i. Dora has been remarkably potent for a long time – the storm has logged more hours as a category 4 hurricane than any other in reliable records for the Pacific that go back more than 50 years (see more on Dora below) – but the storm has also remained quite compact. Moreover, its center took a westward path that stayed more than 700 miles south of the island. Dora’s tropical-storm-force winds extended no more than about 150 miles north of its center, and surface pressures were higher than average across most of the area between the islands and Dora when the fires erupted (see Figure 1 below).
Some of the high pressure between Dora and Hawai‘i was likely induced by the hurricane itself. Rising air within a strong hurricane is typically balanced by descending air on the fringes of the storm. As that descending air warms, it can lead to clear skies, high surface pressures, unusually hot conditions, and fire-favorable weather. A case in point is Hurricane Lane of August 2017, which angled northward and passed much closer than Dora to the Hawaiian Islands. Lane brought the heaviest rains ever recorded from a tropical cyclone in Hawai‘i to the Big Island. Yet strong winds on the periphery of Lane triggered multiple wildfires on Maui and O‘ahu, as detailed in the study “Fire and Rain: The Legacy of Hurricane Lane in Hawai‘i.”
The resilience and strength of both Dora and the surface high north of Hawai‘i may both be linked to larger-scale dynamical features that have kept both Dora and the high pushing westward over the past several days. In similar fashion, Hurricane Ophelia – which passed northward well off the coast of Portugal in October 2017 as the easternmost hurricane on record for the Atlantic – was embedded within, and helped reinforce, a large-scale steering flow that drove hot, dry southerly winds across the Iberian Peninsula, stoking wildfires that took at least 49 lives in Portugal and Spain. Such events are often considered compound disasters, as they involve multiple factors that add up to a disastrous sum greater than its parts.
Drought and dry air — both local and imported
Many of the western (leeward or downslope) parts of the Hawaiian Islands, including much of West Maui, have arid or semiarid climates. Much like Southern California, rainfall is concentrated in the late fall through early spring, and drought conditions are common in summer. Long-term warming tends to make even naturally occurring periods of drought hotter, thus parching the landscape more readily.
According to the U.S. Drought Monitor, the western coast of Maui was experiencing moderate to severe drought as of Aug. 1. As shown in Figure 3 below, drought conditions in August were more intense during the La Niña years of 2020, 2021, and 2022 than they are right now. So while the current drought is not exceptional, it was enough to help create a fire-friendly environment when the fierce, dry downslope winds arrived.
The increasing presence of large swaths of flammable nonnative grasses also contributed to the wildfires. As noted in a state hazard mitigation plan, “The State of Hawaii’s native ecosystems are not fire adapted. In many cases, once an area burns, it is replaced by fire-prone non-native species, permanently changing the State of Hawaii’s landscape.”
It’s also possible that the record-hot air mass over the U.S. Southwest — whose unprecedented heat has been deemed virtually impossible without human-induced climate change — played an indirect role in the Maui fires. Upper-level steering currents around the massive high appear to have pushed a wedge of unusually warm, dry air, extending several miles above ground level, westward all the way to Hawai‘i, as shown in the animation embedded below (the acronym PGF refers to pressure gradient force, which is proportional to the difference in high pressure and low pressure across a given distance). This air mass would have then descended the tall slopes of Maui into areas that ultimately burned.
A formal climate attribution study would help shed light on how much the factors above played into the catastrophic compound disaster across Maui, and how likely or unlikely it is that they would have come together as they did in the absence of climate change.
Assuming the fires in Maui were at least partially Dora-related, then Dora is the second tropical cyclone to affect Hawai‘i so far in 2023. On July 18-19, Tropical Storm Calvin passed about 100 miles to the south of the Big Island with sustained winds of 45-50 mph. Calvin brought widespread rainfall amounts of two to four inches to the Big Island and Maui, which caused minor flooding and scattered power outages. A few locations on the Big Island received rains of five to seven inches, according to the final report from the National Weather Service.
A 2016 modeling study found that we could expect to see a significant increase in hurricanes near Hawai‘i in coming decades due to climate change; see also Jeff Masters’ August 2014 post, Climate Change May Increase the Number of Hawaiian Hurricanes. Only five named systems at tropical storm strength or higher have made a direct landfall in Hawai‘i since modern recordkeeping began in 1949.
Forecast for Dora
At 11 a.m. EDT Thursday, Dora was still a category 4 hurricane with 140 mph winds, located 1,010 miles southwest of Honolulu, Hawai‘i, and headed just north of due west at 22 mph. Dora is expected to weaken only very slowly and will likely cross the international date line by Friday night as a category 3 storm, becoming Typhoon Dora in the western Pacific. Only three other central Pacific major hurricanes have been recorded to cross into the western Pacific and become major typhoons there: Genevieve (2014), Ioke (2006), and John (1994). By early next week, Dora will move more to the northwest and encounter cooler waters and higher wind shear, which will put an end to this unusually long-lived storm. Dora is not a threat to any land areas.
Hawai‘i fires punctuate a mostly quiet year for U.S. wildfire
Although Canada is having its worst wildfire season in modern history, and sending massive volumes of smoke into the United States, the U.S. itself is having its least-fiery year in more than a decade. As of Aug. 9, 2023 has been the least active for U.S. wildfire in terms of acreage burned since at least 2013, according to statistics from the National Interagency Fire Center. This year’s U.S. fires (including those in Alaska and Hawai‘i) have burned 1,411,277 acres through Aug. 9, which is only about a third of the annual average up to that date across the last 10 years. In the center’s full-year database, which goes back to 1983, every year since 1998 has ended up scorching at least 3.4 million acres by Dec. 31. It remains to be seen how long residual moisture from the notably wet winter of 2022-23 will help keep landscapes across the western U.S. relatively fire-free.
CNN is offering a link to help wildfire victims in Hawai‘i. Donations can go to multiple nonprofits: the American Red Cross, Maui United Way, Maui Humane Society, and Salvation Army.
Website visitors can comment on “Eye on the Storm” posts (see comments policy below). Sign up to receive notices of new postings here.