The Origin of the Hawaii Fires/Preventing a Similar Tragedy in the Future

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.

Flying into Maui in late June.  

Dry grass everywhere (looking north along the West Coast of Maui)

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.

The Winds

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.

NOAA map of the path of strong winds from Hurricane Dora

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.

Ignition

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.

 Powerline De-energization

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.

Wind-Driven Wildfires on Maui

Large fires are now burning on Maui, Hawaii with severe damage to the historic town of Lahaina on Maui's west side.

Downtown Lahaina burning.   Picture courtesy of Alan Dickar

Satellite imagery shows two major fires... one near Lahaina and the other in the high country east of Kihei (see images below, the orange and red dots show the fires).

As I will discuss below, these fires are the results of strong winds and bountiful grass, plus human ignition sources.  Wetter and cooler than normal conditions during the past six months played a role.

Wildfires and Hawaii

Believe it or not, Hawaii is one of the most fire-prone states in the U.S. (see map below of some historical fires)

With persistent trade winds out of the east or northeast, the eastern side of the Hawaiian Island is quite wet (with moist upslope flow), while the lee (or Kona) sides are dry (see climatological precipitation map of the Hawaiian islands below).

That is why many people vacation at Kona (Big Island), Lahaina (Maui), or  Poipu Beach (Kauai), where warm, dry weather dominates.

There is sufficient precipitation on the lee side of the islands for substantial grasslands to develop, with grasslands increasing during the past several decades as agriculture has declined on Hawaii (e.g., the sugar cane industry is essentially gone).  

To illustrate, here is an image taken by Google near Lahaina.  Lots of grass.

An inferno ready to happen.

You can also view the large grassy areas on Maui on this satellite image (grassy areas are brownish in color)

Such grasses are highly flammable, even a day after rain, with fire growth greatly encouraged by strong winds. Much of the grasses on Maui are non-native, invasive species that burn easily.

And Hawaii frequently gets strong trade winds.

Why did the Maui fires happen now?

Very strong trade winds developed yesterday, as a large pressure difference (gradient) formed between a strong subtropical high and hurrican Dora to the south.

To show how unusual this pattern is, the figure below shows the sea level pressure at 11 PM PDT last night, and the normalized anomalies from the typical sea level pressure (colors). 

MUCH higher pressure than normal was found just north of Hawaii (red and brown colors), while an area of lower than normal (blue colors) was found south of Hawaii (due to Hurricane Dora). 

The result of this anomalous pressure pattern was greatly enhanced winds that fanned the flames and I suspect helped start fires (by downing powerlines).   A familiar story to those of us in the Northwest.

How strong were the winds?     Below are the maximum gusts on Tuesday provided by a NOAA website--some as high as 62 mph.  Other reports were as high as 80 mph.

Model simulations/forecasts suggested strong wind acceleration on the lee slopes of the substantial terrain of Maui and downstream of gaps in  its terrain  (the University of Hawaii high-resolution surface sustained wind prediction for 6 PM PDT Tuesday is shown below)

The situation this year on Maui was made even more dangerous on Hawaii because the past half-year was WETTER and COOLER than normal, which enhanced grass growth.   I repeat wetter and cooler.    

I don't have to tell you what some media will be ascribing the Hawaii wildfires to:  climate change.   Demonstrably untrue.

To demonstrate wetter/cooler conditions, here is the departure of precipitation from normal for the past six months (in inches).   Western Maui was wetter than normal.  Much of the big island was crazy wet.  This excessive moisture was the result of several powerful Kona Storms this winter.

Temperatures the past six months?   As shown below, a bit below normal over western Maui.

So we started with a region prone to grassfires (the western side of Maui).   We had enhanced grass growth due to extra precipitation, and then the area was hit with unusually strong winds.

Many of the same ingredients came together to produce the recent large grass fires in eastern Washington.