From The Cliff Mass Weather Blog
The terrible fires around Lahaina, Maui have resulted in a death toll of 67 (which will certainly rise) and an economic loss of billions of dollars.
We can take steps to prevent this from happening again, including understanding why this event occurred and building the observation, warning, and action infrastructure as California.
Why did this event occur?
The origin of this disaster is now becoming clear: massive amounts of dry, dead fuel (mainly grass), strong downslope winds produced by strong trades interacting with local mountains, and human ignition, most probably from powerlines.
Dry grass and shrubs
Maui was a tinderbox ready to burn explosively. As noted in a number of articles and Hawaiian government websites, a large portion of Hawaii is covered by highly flammable, invasive, non-native grasses.
Western Maui is typically wet in the winter and quite dry (and warm) during summer (see plot for a station near and north of Lahaina). Grass grows during the winter and then dies/cures during the summer, leaving brown desiccated grass. This is not climate change…this is the normal situation.
This year the winter was particularly wet, enhancing Maui grass volume, followed by a dry summer. A huge supply of dead fuel was ready to burn.
There has been a lot of talk in the media about drought and even “flash drought” driven by climate change (see Seattle Times headline below). This is all silly and irrelevant. The opposite of drought last winter resulted in lots of grass and even a normal summer would have resulted in the grass ready to burn now.
Also important is that the grasses are 1-10hr fuels that dry within hours under the proper conditions (low relative humidity, winds, sun). The conditions earlier this week were optimal for drying with warm, dry, downslope flow. The grasses could have been drenched a few days before and burned under such conditions. Climate change is irrelevant in this situation.
Lahaina was hit by powerful winds, with gusts exceeding 60 mph.
Winds that provided oxygen to the fires, pushed the fire quickly forward, and downed powerlines, helping spark the fires.
There is a lot of talk about the winds coming from hurricane Dora, which passed 800 km to the south of Hawaii (see satellite image below).
The winds that hit Lahaina were NOT hurricane winds.
The winds that helped destroy Lahaina were caused by strong trade winds, produced mainly by enhanced high pressure to the north, interacting with Maui terrain to produce strong/dry downslope winds.
These were localized strong winds that amazingly were well predicted by the NOAA HRRR model and others.
Hurricane Dora was a small storm that passed well south of Hawaii. The strong winds of the hurricane did not significantly affect Hawaii as some claim.
During the last day UW Research Scientist David Ovens, a member of my research group, ran the WRF weather prediction model at high resolution for this case.
The results are stunning. Below is the 27h forecast of wind gusts at 8 PM PDT on Tuesday, Aug. 8th. Gusts to around 65 knots (75 mph) around Lahaina (color shading). Pressure is also shown as are the wind vectors. A life-threatening prediction.
Moderate winds approached the mountains of West Maui and then accelerated down the western slopes of the terrain. A stable near crest level assisted.
Strong winds were also observed over central Maui west of Haleakala volcano: more grassfires occurred there.
Let me repeat: these were NOT hurricane winds but local downslope wind accelerations, produced by the occurrence of perfect meteorological conditions, something I will review in a future blog.
An analog to such wind acceleration is the strong winds that can occur in Enumclaw, Black Diamond, and North Bend, Washington under strong easterly (from the east) flow.
Although little information has been forthcoming on this point, the ignition had to be human-caused, since there was no lightning in the area. Considering the massive wind damage to electric infrastructure, with reports of fallen and sparking powerlines, it is quite probable that the strong winds caused the ignitions that started the fires.
We Can Make Sure This Never Happens Again
First, it is essential the actual causes of the fire be understood (extensive dry grass, strong local winds), not climate change and “flash droughts.” Only a science-based, rigorous understanding of the wildfire’s origins can lead to a better outcome in the future. Incorrect, politized explanations work directly against solving the problem.
Second, many more wind observations are needed. The weather observing network on Maui and particularly western Maui is totally inadequate, as shown by the map below.
Virtually no wind observations around Lahaina. Unbelievable. Weather observations are critical for understanding the wind threat, to warn the population. Wind observations foster decisions to de-energize powerlines to prevent ignitions.
California has learned this lesson and has installed thousands of weather observation sites. Hawaii needs hundreds.
Third, much better use of weather forecast models for warning and decision-making is required. As shown above, current weather prediction technology is so good that most localized wind threats can be forecast well in advance.
The National Weather Service waited way too long to put out a Red Flag Warning (9:26 AM on August 8th). And with the intense winds predicted by the NOAA HRRR model, MUCH more severe warnings should have been made. NOAA and the State of Hawaii need to work out a comprehensive plan for better warning of such dire threats to life and property.
Hawaii electric utilities should immediately make plans to turn off the power to threatened areas when strong winds are either observed or predicted. California and Northwest utilities have already begun this life and pre
The combination of rigorous science, more observations, better use of models, stronger and more aggressive warnings, and powerline de-energization can ensure that a tragedy like this week will never occur again in the Hawaiian Islands.