ORLANDO, Fla. – Several large, out-of-control wildfires broke out Tuesday on the Hawaiian islands. Western Maui, specifically the historic town of Lahaina, was hit the hardest.
A hurricane, high pressure, an ongoing drought and Hawaii’s terrain combined to create the catastrophe.
Setting The Stage
The western side of the Hawaiian islands are typically the drier side due to their location relative to the higher terrain. It’s why the resort towns are on this side of the islands. The trade winds supply ample Pacific moisture on the windward, or eastern side of the islands.
This year, however, Western Maui was drier than normal, in a moderate-to-severe drought, according to the United States Department of Agriculture.
This, of course, means a lot of already dry vegetation, providing fuel for wildfires.
Meteorological Setup
Category 4 Hurricane Dora was passing safely, about 500 miles south, by the Hawaiian islands.
While the storm did not directly impact Hawaii, it combined with a large area of high pressure in the North Pacific to create a large pressure gradient.
Air blows from high to low pressure. The larger the difference in pressure, the stronger the winds. In this case, the islands experienced very strong winds out of the northeast as a result of the two systems. Winds gusted between 50 and 80 mph, allowing any fire that started to spread rapidly.
Hurricanes also promote air to sink on the outer edges of the storm. Some of the nicest, driest and hottest weather is before and after a hurricane. This contributed to drying out the atmosphere.
The Terrain
Western Maui is typically dry because it’s in the rain shadow of the mountains to its east. As the trade winds come off the Pacific, air is lifted up and over the mountains. The air then descends down the other side of the mountains and dries out.
Lahaina sits at the base of the mountains and is typically warm and dry because of this.
When air sinks, it dries out and warms up. This creates extremely dangerous fire conditions given other favorable meteorological factors. This is similar to what happens when Santa Ana winds are induced in California.
The ongoing drought set the stage for vegetation to burn easily. The large difference in pressure between Hurricane Dora and the North Pacific high created extremely strong winds to fuel and spread the fires rapidly. The drying and warming nature of down-sloping winds made this situation even more dangerous.
Red flag warnings were in effect from the National Weather Service, indicating the critical fire danger.
The cause of what started the actual fires has yet to be determined.