November 22, 2024

Are Eastern Pacific Cyclones Become More Frequent or Stronger?

 During the past three days, I have received several calls from media folks asking the same question: 

Are storms like this week's "bomb" cyclone becoming stronger or more frequent due to global warming? 

If not, will global warming cause such increases in the future?

The answer to these questions is quite clear:  NO.

There is convincing scientific evidence that our region has not seen an increase in such storms and that a warming planet will not bring more meteorological "bombs" into our region.

First Some Terminology

A midlatitude (or extratropical) cyclone is a low-pressure center with winds rotating counterclockwise around it in the northern hemisphere.   The strength of the cyclone is generally quantified by the central pressure, although size is also important.  Generally, the lower the central pressure, the stronger the cyclone and the more powerful the winds.

As shown by the figure below, cyclones generally form in regions of strong horizontal temperature change....in fact, such temperature contrasts are the fuel of such storms.


Regarding central pressures, garden variety storms in our region have pressures around 990-1000 hPa.   Strong storms perhaps 980-990 hPa, and powerful cyclones have pressures of t965-980 hPa, with extreme storms even less.

Tuesday's storm dropped to an astounding 943 hPa, tying the record for the past 70 years.

Cyclones that rev up particularly rapidly are called "bombs".....and the media has certainly fallen in love with this term.   By definition, bomb cyclones deepen by 24 hPa or more in 24 h.  This definition is completely arbitrary.  Really just for fun.

Are Local Cyclones Getting Stronger?

The answer is clearly no.  There has been no increase in the frequency or intensity of landfilling or near-shore cyclones in our region.  

Most of the famous local cyclones occurred during the early to mid-20th century, with the last major landfalling cyclone in 2006 (the Chanukah Eve Storm).

Another way to demonstrate the lack of increase in storms is to plot sea level pressure over time at a point on the Washington Coast (Ocean Shores).   As shown below, there is no evidence for an increase in the lowest pressures (say below 980 hPa).


Will Global Warming Increase Strong Windstorms Over the Region?

A group of us at the UW (in association with the UW Climate Impacts Group) did a formal study of this question, funded by Seattle City Light.  

We made use of a state-of-science regional climate model driven by an ensemble of Global Climate Models.   

This research did not find an increase in extreme winds over the region (we examined several locations).  A graphic from the analysis of the extreme wind trends through the end of the century is shown below.

There are good scientific reasons to expect little change in the intensity of midlatitude cyclones over our region.

For example, global warming preferentially warms the Arctic in the lower atmosphere, thus weakening the north-south temperature difference that drives the storms.   On the other hand, the temperature change is strengthened aloft, with the result being a wash for the storms.

In summary,  natural variability and processes sometimes can come together to produce very intense cyclones like the one we experienced on Tuesday.

We experienced a rare, extreme event and there is no reason to expect that such storms will become more frequent as the planet slowly warms.








22 comments:

  1. Yesterday November 21, 2024 a day after the wind storm in Western Washington State. Kodiak City, Alaska had a record high temperatures of 58 F.

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    1. I wonder how much of their warm air originated as our downslope winds, flung around the NE side of the cyclone up their way.

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  2. "By definition, bomb cyclones deepen by 24 hPa or more in 24 h " is only true at 60° latitude.
    Per Sanders and Gyakum (1980) the deepening rate qualify as a meteorological bomb (MB) is less at lower latitudes as follows:

    MB ... where 24 hPa / sin (latitude°)
    24 / sin(60°) = 24 hPa
    24 / sin(40) = 21.8 hPa
    24 / sin(30) = 12 hPa

    Of historical note .. nowhere in the 1980 paper does the term 'bomb cyclone' appear yet it's referenced time and again as the source of the term.

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    1. CORRECTION: should be divide by sin(lat°) / sin(60°)

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  3. Cliff, why is the term "bomb" used to describe a sudden decrease in pressure? Isn't a bomb something that produces the opposite.. a sudden increase in pressure?

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    1. Sanders and Gyakum described the rapid deepening as 'explosive' cyclogenesis and as well can all attest ... bombs are explosive.

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    2. I saw that - it doesn't answer my question. Look up "explosive" as it relates to pressure.. "a rapid development of high pressure".

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    3. the context: bombs explode ... right?

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  4. Interesting that in the Atlantic the warming ocean is increasing bomb cyclones but not in the Pacific.
    "Data from the National Weather Service (NWS) indicates that bomb cyclones are becoming a staple of winter weather, particularly along the East Coast. Between 1980 and 2020, the number of bomb cyclones in the Atlantic basin increased by approximately 40%. This trend is partly driven by warmer ocean temperatures, which provide the energy needed for rapid storm intensification."
    https://www.environmentenergyleader.com/stories/novembers-bomb-cyclone-what-it-tells-us-about-the-rise-of-extreme-weather-in-the-us,57840

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  5. I think we have to replace the term "bomb cyclone". The poet in the "Climate Lab" at Seattle Times repeated the term many times in the past few days. Apparently it's great clickbait.

    What would be a good (or phrase) to replace bomb cyclone? Low Center Pressure Anomaly Storm? (LCPAS)

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  6. Because I grew up in the NW, and experienced the Columbus Day storm in 1962, and most of the powerful storms since, I can relate to the temptation to over dramatize them. But I know from research that they happen in both the northern and southern hemispheres and that while our damage is very real our extra tropical cyclones are not the worst nature creates, and the damage not the worse, historically. Professor Mass can verify or discount it but I read a paper that asserted an extrapolated pressure of <900 hPa for one storm in the southern Pacific, and deaths in the thousands resulting from one in the northern Atlantic in the early 1700s. I wish news sources exercised more restraint but a large percentage of the public likes exaggeration and it sells advertising for news sources.

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    1. I too experienced the Big Blow of 1962...and totally agree with your thoughts concerning the type of occasional intense storms that we receive. Certainly we have had Fall/Winter storms of this type, showing up every year--sometimes as many as a half dozen nasty, yet awesome events. The 1962 storm was "An outlier, fueled in part by the remnants of Typhoon Freda"...We will not likely see another storm of this intensity during my lifetime, or yours!....Professor Wolf Read, who now lives in BC , did a very thorough Doctoral dissertation years ago, summarizing over 50 of the NW bigger storms that have happened over the last 100 years or so. Fascinating reading, and his efforts can be found on his website "Storm King". He is now retired from teaching, but still works, now as a consultant for BC Hydro.

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    2. "We will not likely see another storm of this intensity during my lifetime, or yours!"

      In the case of a storm like that, the probability of it occurring is always the same. The fact that it occurred does not change the probability of it occurring again.

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  7. Regarding the intensity of the storm. I read on your other post that the downslope easterly winds were a major contributor to the damage on the East Side.

    Is it possible that recent deforestation activity could have lead to increased damage in specific areas?

    The damage to Issaquah was severe, but it was particularly intense in our community on Tiger Mountain and the neighboring community of Mirrormont. But what's strange is that if you drive further south along Tiger Mountain Road, there's very little damage overall (much more consistent with the rest of Issaquah). I've consulted the map and it seems quite clear the worst damage is confined to the area directly east of the deforestation that occurred in 2023. Search for articles regarding the Mirrormont community specifically to see what I'm talking about.

    My research skills are quite limited. It seems plausible that the removal of a windbreaking forest in the path of the wind exposed my community to unnecessary damage from the storm. This was apparently true in the case of Hurricane Florence, in which damage to the forests exacerbated flooding and wind damage to structures.

    Given what you've said in this article, I'd love to hear your thoughts on this idea. At the very least, I could push back on the repeated claim that "if only we had implemented a carbon tax this wouldn't be happening!"

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    1. Hopefully Cliff will chime in, but the sporadic areas of severe damage seems to be indicative of mountain wave activity. We have similar areas of sporadic damage in Maple Valley, although not as severe as Mirrormont.

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  8. Hey, news loves scary headlines. It's maybe just that simple. Otherwise, without fear, how are you going to get clicks and viewers? Prior to these two wind events, that fear mongering got downright silly when forecaster were calling for gusts of over 40 around Chehalis on Friday (without even a wind advisory) when Cliff's blog and weather underground called for winds that most wouldn't consider breezy! We're it not for the hype, those in the Lower Chehalis Valley wouldn't have known a windstorm had even happened.

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  9. I've helped clear massive trees that have fallen over each other like Pick-up sticks. And like the game, it is important to remove one from the pile without disturbing any of the others. I recall the bigest tangle I worked at was on a trail on the south side of the Middle Fork Snoqualmie.
    I'm seeing reports and photos from near Issaquah, so I suspect there will be lots of trees broken and/or tipped over in the remote valleys. These will keep sawyers busy and entertained for many weeks.

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  10. Cliff, are you going to comment on this story or post on AI or Microsoft's Aurora?
    https://www.seattletimes.com/business/can-ai-spot-the-next-bomb-cyclone-far-in-advance-microsoft-hopes-so/

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  11. The best news is that you are still being requested to make comments by journalists.

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  12. Cliff, how do you get accurate pressure readings when the storm is over the Pacific?

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Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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