How did the wildfires start in Maui? A combination of factors fueled disaster

Wildfires on the Hawaiian island of Maui have killed at least 93 people, destroyed more than 250 buildings in historic Lahaina Town and forced hundreds to evacuate. Thousands of residents are without power.

It’s the deadliest U.S. wildfire in over a century.

The fires started Aug. 8 and fanned out across the island, growing in size and destructive power. Hawaii declared a state of emergency on Aug. 9.

Although wildfires have quadrupled in Hawaii in recent decades, causes of the fires haven't been determined. But a combination of weather factors generated what the National Weather Service calls “red flag” conditions in which fires are likely to start and spread.

In Hawaii, those factors include:

  • Gusting winds
  • Low humidity
  • Lack of rainfall
  • Dry vegetation

Winds: Gusting winds spread and channel wildfires by increasing the oxygen supply to the flames and carrying burning material ahead of the fire.

Hurricane Dora, a Category 4 storm hundreds of miles south of the islands, generated maximum sustained winds of 145 mph, with gusts up to 170 mph, AccuWeather reported.

Wind gusts on Hawaiian island

Dora did not directly hit the islands, but it helped set up conditions ripe for a disaster, the National Weather Service said. A high-pressure system developed north of the islands, resulting in gradient winds between the high pressure and Dora, a low-pressure system. That increased wind gusts across the islands, with a peak gust of up to 67 mph early Wednesday in Maui.

Humidity: Hawaii is experiencing low humidity levels. Relative humidity, the amount of water vapor in the air at a set temperature, also affects wildfires. If humidity is low, vegetation such as grass and pine needles dries out more quickly and becomes more combustible.

Rainfall: Rainfall in Hawaii has declined significantly over the past 30 years, the state government says. About 90% of Hawaii receives less rain than it did a century ag

Dry vegetation: The spread of invasive plants such as guinea grass and fountain grass have helped spread fires. The grasses now cover a large

CONTRIBUTING Claire Thornton and Marc Ramirez, 

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