August 15, 2023

The Real Cause of the Maui Wildfire Disaster

This blog will discuss the key reason for the Maui disaster, one not discussed by the media and others:  a high amplitude atmospheric wave forced by strong winds interacting with the mountains of northwest Maui.  

An atmosphere wave that produced powerful, dry downslope winds on the western slopes of West Maui mountains.

A vertical cross-section of the predicted mountain wave.  
Explained in detail below

The terrible disaster in Maui has been leading the news cycle for a week now, with media and others proposing many causes:  climate change, drought, dry invasive grasses, and Hurricane Dora to name a few.

But none of them have identified the key reason why so many people died last week and why the damage was so extensive.  None explained the 60-90 mph gusts that hit a very localized area.  Winds strong enough to shear off wooden power poles, tear roofs apart, and down lines of power lines.  

And it wasn't Hurricane Dora, a relatively small tropical storm that passed 700 miles to the south of Hawaii.

Something else happened in Maui last week.   Something capable of creating intense wind damage in one location and light winds a few miles away.

A phenomenon skillfully predicted by modern high-resolution models, and thus a feature we could have warned Lahaina's population about.   A phenomenon that would have been picked up by surface weather observations, if only West Maui had invested in inexpensive weather stations.

The Terrain

To understand what happened one must consider the terrain of West Maui (see below), which is dominated by terrain reaching approximately 5500 ft.

Looking eastward from a boat off of Lahaina, the terrain looms impressive (see below).

Picture courtesy of Professor Dale Durran, UW

Last Tuesday, strong winds approached the crest of the West Maui Mountains, not because of Hurricane Dora, but because of an unusually strong high-pressure area to the north.  

We know this for several reasons.  A map of sea level pressure (black lines), surface winds (wind barbs), and the standardized sea level pressure anomaly (difference) from normal (colors) at 9 AM Hawaii time on Tuesday are shown below.  

High pressure is centered north of Hawaii and this high pressure was far more intense than normal just north and over Maui (indicated by the orange, red, and brown colors).   The pressure anomalies due to the Hurricane Dora were very small in scale and limited to far south of Hawaii.

Hurricane Dora had little impact on Hawaii during this event, something confirmed by an expert at the National Hurricane Center.

Since winds approaching the West Maui mountains will be so important consider the situation at the same time for an elevation of around 2600 ft (925 hPa pressure)-- see below.   You can see the high to the north, the location of Maui (white arrow), and the hurricane (red arrow).  

The wind anomaly from normal of the winds at this level is shown in color.   Look carefully and you will see gray color over Maui.... five standard deviations from normal....which means VERY unusual.  You will also note the clear separation of the strong winds of Dora from what hit Maui.

Not not only were strong winds approaching the West Maui mountains, but another feature that can foster a very strong mountain response also occurred:  an area of stable air near the crest level of the terrain.

This is illustrated by the vertical sounding at Hilo on the Big Island six hours earlier (see below).  The black line on the right shows the temperature with height.  When the temperature does not fall rapidly with height, the atmosphere is generally stable. When it is constant with height or warming with height (an inversion), it is very stable.

Trust me, this stable layer is important.  When strong winds accompanied by a stable layer near or just above crest level hits a terrain barrier, a high-amplitude mountain wave can form.

A wave that can produce intense downslope winds.

And this is exactly what happened last Tuesday over Maui.

The Smoking Gun

Last week, I asked David Ovens, a highly skillful atmospheric modeler in my group at the UW, to run a forecast of the Maui event using the WRF model at very high resolution (1.3 km grid spacing).

I was stunned by the simulation, which revealed the real cause of the disaster:  a high-amplitude mountains wave with very strong downslope flow on the West Maui Mountains.  

Below is a  forecast vertical cross-section of the situation around 2100 UTC August 8th (11 AM Hawaii time).   Winds are shown by color shading and arrows.  The solid lines are potential temperature.

An extraordinarily high amplitude wave had formed, with air descending the western side of  the Maui Mountains, accelerating as it plummeted towards Lahaina.   At low elevations, the flow abruptly ascended, in a feature often termed a hydraulic jump.

Analogous flow can occur for water flowing over a dam.

The descending flow was not only strong, but very, very dry, as shown by the vertical cross-section of relative humidity (see below).  Relative humidities below 20% descended down the mountains, with the driest air well under 10%.

The combination of strong winds and dry air hugely promotes fire, including rapidly drying surface fuels such as grass. 

It did not matter whether the grass or light vegetation were wet or dry the days or weeks before:  this extraordinary atmospheric animal would ensure they were dry enough to burn.   Prior dry conditions during the weeks before were immaterial.

Lack of Wind Observations on West Maui:  How Do We Know the Model Forecasts are Correct?

The lack of wind observations on West Maui is stunning. I know of no other heavily populated areas with such a singular lack of wind observations.  Very bad.

So how do we know these model simulations are correct?

First, there is the damage, even before the fires got going.   Power poles snapped in two.  Powerlines down.  Great physical damage to structures.    Such damage is consistent with winds gusting to 60-90 mph.  

Second, there are videos indicating such strong winds, and a number of people estimated wind gusts over 60 mph.  Check this video.

Maui's lack of observations is not responsible and cripples the ability of the county and local authorities to warn people of such events.

Confirming the Model's Prediction on Hawaii

Similarly strong winds were predicted by the model over the northwest side of the Big Island, where strong flow hit similarly high terrain (see map below and wind forecast beneath it)

Strongest winds indicated by the orange color

But unlike Maui, we do have a good observation on Hawaii, at the USDA RAWS site at Kohala Ranch (see red arrow above).

During this event, the winds gusted to 82 mph! (see proof below).  Confirmed!

The Bottom Line

The Maui event was the result of a high amplitude mountain wave and strong, dry downslope flow on the western slopes of the mountains of West Maui.   The mountain wave was the result of strong approaching flow and a stable layer near the crest level of the Maui Mountains.  

Strong dry winds support fire and result in rapid movement of the flame front, as well as moving embers ahead.  The winds could well have started the fire by damaging infrastructure.   As noted in my earlier blog, a huge reserve of dry, flammable grasses was in place.

This event was not the result of climate change, Hurricane Dora, or an extended drought.  It resulted from an unusually intense mountain wave/downslope windstorm produced by a fairly rare convergence of conditions.

This event was highly predictable using modern weather prediction technology.  The combination of a reasonable weather observing network (which does not exist on Maui) and the use of state-of-science weather modeling, the population of Maui can receive far better warnings that can prevent this tragedy from occurring again.


  1. Fantastic analyses – thanks.
    I suspect this wasn't the first time a high amplitude wave came down on the area of the city. I could not find early weather reports, maybe because the place has had a tough history since the first new settlers came. Someone likely will be able to find a few news items.

    History is here:

    [I watched wind take trees down when I was about 8. I ran past one in the yard, and it followed me as it fell. Had it been 10 feet taller the encounter would have been physical.]

    1. Indeed John, not the first time! Strong localized winds are common enough to get a special name the "Lahaina winds". Cliff's excellent analysis shows why. I included this in my recent tweet Undeniable Proof that Alarmist Climate Scientist Michael Mann is Dishonestly Duping the Public About a Climate Crisis! with a little wind history:

      "Being the furthest Hawaiian island to the north, Maui is affected by stronger northern trade winds that intensify as the normal high-pressure system strengthens each summer. Maui’s topography further intensifies those winds through the mountain valleys. Strong downslope wind events reaching 80 to 100 mph every 8-12 years have "demolished buildings, overturned large power transmission line towers, and uprooted trees." Once or twice a year strong but more moderate winds occur. During the fire, 30 to 40 mph winds with gusts up yo 67 mph fanned the flames. These winds got a special name, the Lahaina Winds. Locals also call them "Lehua winds" after the red blossoms of the ʻōhiʻa lehua tree that shower the landscape during such events. The Lehua winds have been officially reported in the 1995 "A Natural History of the Hawaiian Islands" and in 1985 research reports. Even the writes about these Violent Winds on Maui. "

    2. Maui is NOT the furthest Hawaiian island to the north.

    3. Yes, that was poorly written and has been corrected in the original post. It was supposed to have said "Maui is farther north of Hawaii (the big Island)

  2. What's also not being covered is the widespread failure of the island's emergency warning system. While the sirens went off multiple times during the previous days leading up to the fires, residents ignored the warnings, as most of these events in the past are negligible. However, this time the horns didn't go off, because of a small tremor the day prior, leading to a power outage. No texts were sent when things became critical, and there was no power redundancy regarding the emergency system. The residents who were able to escape only got out because their smoke alarms went off in time.

  3. Excellent post! What would it take to get a reasonable observing system on Maui?
    Has the high pressure migrated east and become the heat dome over us now?
    And, if it continues east could we get similar down slope winds here?

  4. Cliff, kinda off topic, but closer to home. 1) Current heat wave, would we have similar temps to "heat dome" if it had happened end of June or would the higher sun and longer days just be a couple degrees warmer.
    2) Winds end of this wave Friday and low relative humidity has triggered fire weather watch here. (Okanogan Valley and others). Can you explain more in depth and maybe talk about the diurnal shifts we get that increase the danger of fighting our fires. Fought fire 15 years and the wind shifts in evening are almost clockwork and though we know about them the intensity of the shift would sometime catch us off guard.

  5. Your analysis of the winds don't match what I observed on Maui before the fires broke out. I was on West Maui for 10 days prior to the wildfires and the winds were pretty normal for that time of year (I've traveled there for over a decade). Also, because I grew up on the Gulf Coast and often track hurricanes I had been monitoring Dora. First, Dora was a strong CAT 3/4 hurricane as it approached South of the islands. Secondly, when I left on Monday the 7th the winds changed significantly across the entire island. In fact, it was difficult to even keep the car on the highway approaching the airport in Kahului Monday afternoon. Having seen hurricane winds many times before, I can tell you the wind shifts that occurred that day appeared to be related to the storm. Also, given the strength and location of the storm at the time it defies logic that this wouldn't have had a significant effect on the changes in the winds I witnessed. Clearly you're analysis says otherwise, but it simply doesn't match the facts on the ground last week.

    1. are claiming things with no evidence. The hurricane was well south of Hawaii. What is your evidence it had a strong impact? Just because you experienced gusty winds going to the AP says nothing about the hurricane..cliff

  6. Would you describe this wind event as a Williwaw? Experienced one up in Alaska on the boat and it went from Calm to like 60mph for maybe 10 minutes.

  7. About ten years ago, one of our localized, powerful storms hit the Seattle/Everett area...I knew from past experience (1962 Columbus Day Storm) that the gusts I saw might be in the 60+mph range...When I stepped outside, the oncoming serious wind blast made it hard to breathe!...Then I heard a crack! My neighbors's 70' fir tree blew down, into the yard behind me. Once those 60mph winds ramp is no joke!...The type of damage you describe in those instances was very evident back in 1962...Gusts hit up to 100mph during that (hopefully) once in a lifetime event.

  8. There's already a book about this on Amazon!

    Fire and Fury: The Story of the 2023 Maui Fire and its Implications for Climate Change Paperback – Aug. 10 2023
    by Dr Miles Stones (Author)

    So sickening.

    1. I looked at the authors background and he has been publishing different books every few days lately. Made me wonder how many are AI products!

  9. Those same events happen on the northern Olympic Mountains at times, my folks live on the hills south of Joyce at 1000 foot elevation and 9 years ago their neighbors Davis weather station clocked a gust at 112mph, the wind seemed to bounce down the hillsides taking out areas of trees in a wave like pattern, I would imagine Mountain wave events in the foothills of the cascades are like what happened to Hawaii

  10. Amazon is now refusing to let anyone comment unless you are verified buyer of this garbage book

    1. As much as it pains me to defend Amazon, this is common practice and not because they're trying to boost some junk self-published nonsense. I have a family member who self-published a non-fiction book and Amazon did the same for them. I think it's done to prevent buying bogus positive reviews.

  11. This is an excellent post! Could this (and many of your other posts) be spread across mainstream media?! Please?! It's frustrating how the facts, the science are not used to drive efforts and policy. Such wasted resources when this doesn't happen. Sad! Thank you professor Mass. I love your blog posts, the science behind them, the detail, the facts, etc.

  12. Next time someone tells you that the government is the solution to the "climate crisis," ask them about this issue regarding the Maui fires:

    This site is funded by a one of the founders of PayPal who's also a well known far left supporter and advocate.

    1. I'm sure there will be plenty of blame to go around. You're placing focus on the state government to illustrate how in general, the government is ill equipped to handle the negative societal impacts of climate change. Others my place blame on Hawaii Electric, a private company. Regardless, as individuals and private entities continue to not make any progress mitigating factors contributing to climate change, it will likely require a centralized, enforceable public response in the future. Big, global problems require big, global solutions.

    2. John, what's with the mocking tone? Do you not agree that climate change is a global issue requiring a global response? Nobody is saying that "climate change" directly caused this fire. As mentioned by here by Cliff and most major media publications, strong winds directly led to the high intensity of the fire. Climate change, as you probably would guess, has a more generalized influence on conditions influencing the probability of these types of events (although also having the lowest confidence in terms of direct attribution). Could and would they occur without the effects of climate change? Absolutely.

  13. I had read others that brought up a wind wave event, but you folks (UW Atmosphere Dept.) provided the first modeling I had seen. The source of the high pressure to the north is interesting. I do not know enough to tell if Dora helped that area of high pressure and very dry air from or simply was itself caught up in the overall air circulation that developed associated with the high pressure that developed southwest of the US mainland around the heat in the southwest US leading that then moved to the location north of Hawaii. A north Pacific high is not unusual, so it is interesting to know what was different about this one and could perhaps provide a longer term warning.

  14. "irresponsible" might be a more careful word to use there, to avoid
    "Seattle Times: UW researcher says inadequate forecasting 'Not Responsible' for disaster"

    Was the lack of fire on the big island just luck, or did they shut down power lines in affected areas?

  15. Classic Trade wind inversion there about 7,000'

    1. depends on time of the year. In August, the mean inversion base is about 8000 ft. (there is a paper on this). During this event, the stable layer base was pushed closer to the surface, which was probably important for the wave amplification....clif

  16. Impressive post, and it's sad that this perspective dormant exist in the newspapers of record. Where is Danny Westneat?

  17. There are measurements from the Lahaina area, at least until the instruments went down around 7am. They showed swirling wind but mostly side shore (approximately SSE). If you look at the burn tracks, it appears that at least one burn was traveling up the coast from Launiupoko Park (about where the video was taken), which makes me think there was more than one fire that day; the early morning fire near Lahainaluna, the other started at Launiupoko and was pushed NW into Lahaina. The other factor to consider here is that Lahaina suffered the worst damage due to the firestorm but other parts of the island had significant wind damage also - Kihei (south side), Ulupalakua (3000' above Kihei on side of Haleakala), Kula (west side of Haleakala), and Makawao (northwest side of Haleakala). The fire in Kula was definitely traveling upslope. Finally, the high pressure system had existed for a couple days before Aug 8th but on August 7th, the winds were almost calm in Lahaina. The 8th was when the pressure gradient between the High and Dora was the highest. It seems to me that the presence of Dora was a significant factor to what happened on Maui on the 8th. Side note - I surf in Lahaina often so keep track of winds and weather along the west coast. I live on the north shore of Maui.

    1. scott...can you provide me with those wind reports from the Lahaina area? Or tell me how to access them? You can email them to me. The winds were very variable within the east of the pressure trough from the wave. One fire front could burn west and then be advected north. You are certainly right there were other areas of strong winds....the model predicted that. What evidence do you have that Dora was a significant factor? Can you give me your specific evidence?..thanks, cliff

    2. Sure, I will send the wind report. It is for the windsurfing so is not calibrated but I find it pretty close to what I observe. As to whether Dora was a factor - why no downslope wind on Monday (8/7) when the high was just as strong?

    3. I too suspect the lower pressure associated with the passage of Dora had some small effect on the gradient, but just focusing on Dora would be huge mistake. The high pressure build-up in the subtropical gyre is to be expected each summer and increases the pressure gradient. The center of that high pressure does shift and could just as equally triggered the mountain wave. The stable air mass build-up is typical with a tropical inversion layer along with the lack of summer thunderstorms. Other factors affected the height of the inversion.

      The atmospheric circulation creating all this is complex as Cliff has shown. Cliff exemplifies good science that helps us to better understand and prepare for these events. In contrast Michael Mann exemplifies fearmongering and bad science just to push his climate crisis fears by oversimplifying everything to weaponize every event as climate change with no value for predicting such events.

    4. Hi all, I thought I would add to this as it seems similar to my experiences.Thank you Cliff Mass. I have a few questions if you have the time to address?
      As you probably know Maui in that area gets inundated by high winds almost daily. Especially as the land heats up between the two volcanoes. High winds are common on the western side In that area. What also is common as I have noticed is that when ever there is a low pressure system south of the Hawaiian Islands the winds are much stronger in that area. So for example about a month before the fire there was a system farther south and possibly a higher pressure event on the windward side. I surfed an area near Lahaina and the winds were extremely offshore as happens often with a storm to the south. Bigger waves are the draw for me and as the day progressed the winds got so intense I had an impossible time paddling in to waves.
      Additionally that day traffic from Lahaina was blocked heading towards kehei because of a brush fire which has been happening much more often especially since Maui has had less rain between the volcanoes lately. We actually had to find a place in Lahaina to stay for the night. So my main question is if there is a high pressure system on the windward side and an extremely low pressure south of the leeward side wouldn’t that exacerbate the event you described above? From my experience in that area always seems to be the case.

      For me there isn’t a smoking gun. But a series of events that caused this. One of them a large low pressure system that didn’t create wind heading north in that small area but caused winds to increase in intensity heading south because of its larger low pressure system. This happens often in that area from a layman’s point of view. What to me would make this post more complete is if you added more data on if winds are stronger in the past with systems in the south. If that data proves to be wrong then I believe your interpretation would be more accurate. Thanks again for your expertise and time on this. Regardless this information can save lives.

    5. The wind around Lahaina is usually much less than the wind on the north shore around the airport. For instance, for the 3 days prior to the 8/8 (the day of the fire) winds in Lahaina were 10-15 mph, while winds at OGG were 20-30. This is pretty much what you would expect with winds on the lee side of mountains. Trade winds on the north shore of Maui on 8/7 were 35-45 and on 8/8 they were actually less! So the downslope wind-wave is not a function of just the strength of the NPH, if it were, I would have expected to see it 8/7 when the trades were very strong. Anecdotally, every time we get a damaging wind storm here on Maui, there is a tropical low to the south, and this pretty much shapes the forecasts and warnings we get from the NWS.

    6. need to thing about winds at crest level..not the surface. And vertical stability at crest level is also important..cliff

  18. The Hawaiian volcanic peaks are some of the wettest terrain on Earth. The West Maui Mountains are no exception.

    If Hawaii was a well-run state that quit listening to Native Hawaiians who want to block every mountaintop because it's sacred, they could have built a massive reservoir several thousand feet up that would have provided a torrent of firefighting water at a moment's notice. Water fed by gravity requires no electricity.

    Refusal to take adequate precautions against known natural hazards leads to tragedies like this, where children burn to death inside cars. Hopefully the survivors learn and adapt.

    1. You do realize Lahaina is right next to this huge body of water? The thing called the ocean was used to help fight the fire. But the event was too rapid to respond adequately with available units. You would have to have many retrieval systems in place ahead of time. To be fair to your take on this more systems in place would help. Salt water isn't the best for piping as you know but there are systems that work.

    2. Please explain how seawater can be piped upward a hundred feet and to enormous hydrant pressure without an external power source. The utility failed to de-energize power lines that were being blown down by the wind because power was needed to run those essential water pumps.

      If the water is sitting behind a dam at 2000 ft of elevation, valves can be opened manually providing full head pressure even with the power out.

    3. So yes there would be no power to run the pumps if utility cut power. But like a lot of states and municipalities battery arrays are being used. TX for example since they failed with their system and are now using greener power sources as back ups. Ironic. But I digress.
      The installation should be done in accordance with the following:
      - A priming tank should be provided to fill the volume between the backflow preventer and the foot valve (upstream and downstream).
      - Only one pump should be supplied per priming tank
      - The bottom of the priming tank should be at least 1.5 m (5 ft) above the top of the pump
      - Automatically filled tank only are accepted: volume at least 500 l (130 gal.) or 3 times the volume of the suction pipe + pump casing, whichever is the greater
      - If a manually filled priming tank is provided anyway, the minimum volume should be at least 950 l (250 gal.) or 3 times the volume of the suction pipe + pump casing, whichever is the greater. Replacement with an automatic filled priming tank is then advised.
      - The water supply to the priming tank should be capable of keeping the tank full at all times.
      - The priming tank should be connected to the pump discharge upstream of the check-valve, with minimum DN 50 (2 in.) diameter pipe. The connecting point should ensure that all priming water enters the pump and suction side, and is not wasted in the discharge pipe of the pump.
      - The priming connection should be fitted with a gate valve and a check-valve, as close as possible to the pump
      - The priming tank should be fitted with a low level gauge, set at 2/3 of tank volume, to automatically start the pump on a low level condition, and allowing tank refill through a calibrated orifice
      But like I said salt water requires lots of maintenance so fairly costly. If they want to preserve native lands/flora/fauna/etc then it would cost them probably about the same as building a reservoir and dam over the years with a salt water system. I could be wrong though on costs. But you could also power with wind and solar.

  19. Climate change is the answer for everything nowadays when anything bad happens that has a weather component. Social injustice when those events could be envisioned through a lens of inequity.

  20. Just a reminder (and paying attention to previous work on this blog) how important a knowledge of Meteorology is, even in Western Washington (Bremerton, near Hwy 3) ... making decisions about grass fires in WESTERN WASHINGTON. We actually had two yesterday... By reading Cliff's blog I've learned how important atmospheric stability is... and though we had a grass fire about 100' from our house ... TWICE YESTERDAY ... I was critically aware of two facts: 1/ the trees were in good condition (unlike grass which can turn on a dime) and 2/ as a nuclear physicist and WX who did a bit of grad work Meteorology (the basic courses and some Thermodynamics and Optics for my grad minor...) that the atmosphere was characteristically UNSTABLE so smoke and stuff largely went UP.

    My point here is that when making critical 'shelter in place vs evac now' decisions for your family, this blog is ESSENTIAL. I told my family... 'we will spray water on the roof to suppress sparks but if I see the trees go we are evacuating' Cats were in the car and the household was fully raised and responding. We've actually had to do this drill three times in the past year, here in Brem. In October 2022 the trees DID burn... and we left leaving the roof undefended.

    Pix and follow up at (it was supposed to be a coding dojo but ended up being about cats and wildfires... oh well).

    I actually have python code to pull METAR from Bremerton Airport and estimate the Pasquill-Gifford stability but it was obvious on sight yesterday... here's a pic of the code... I won't bother putting it on a website because I'm setting up a 'Wolfram-One' account and that will make it easier for me to push out code... anyway 90% of the time I get a 'neutral' reading ... the reason I do this is Hwy 3 is in a cut pass and I want to estimate pollution at my property line, using EPA codes... but anyone who doesn't think 'situation awareness' involves sensors, coding, intuition, and reading this blog should look at this pic from yesterday, straight off of METAR, and then the burning grass pics... still working on the mold calc...

  21. Cliff. This work absolutely requires peer review publication.


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